Links to: arXiv, form interface, find, astro-ph, recent, 1709, contact, help (Access key information)
In this year, in which we celebrate 100 years of the cosmological term, $\Lambda$, in Einstein's gravitational field equations, we are still facing the crucial question whether $\Lambda$ is truly a fundamental constant or a mildly evolving dynamical variable. After many theoretical attempts to understand the meaning of $\Lambda$, and in view of the enhanced accuracy of the cosmological observations, it seems now mandatory that this issue should be first settled empirically before further theoretical speculations on its ultimate nature. In this work, we summarize the situation of some of these studies. Devoted analyses made recently show that the $\Lambda=$const. hypothesis, despite being the simplest, may well not be the most favored one. The overall fit to the cosmological observables $SNIa+BAO+H(z)+LSS+CMB$ singles out the class RVM of the "running" vacuum models, in which $\Lambda=\Lambda(H)$ is an affine power-law function of the Hubble rate. It turns out that the performance of the RVM as compared to the "concordance" $\Lambda$CDM model (with $\Lambda=$const.) is much better. The evidence in support of the RVM may reach $\sim 4\sigma$ c.l., and is bolstered with Akaike and Bayesian criteria providing strong evidence in favor of the RVM option. We also address the implications of this framework on the tension between the CMB and local measurements of the current Hubble parameter.
We investigate the evolution of the dark matter density profiles of the most massive galaxy clusters in the Universe. Using a `zoom-in' procedure on a large suite of cosmological simulations of total comoving volume of $3\,(h^{-1}\,\rm Gpc)^3$, we study the 25 most massive clusters in four redshift slices from $z\sim 1$ to the present. The minimum mass is $M_{500} > 5.5 \times 10^{14}$ M$_{\odot}$ at $z=1$. Each system has more than two million particles within $r_{500}$. Once scaled to the critical density at each redshift, the dark matter profiles within $r_{500}$ are strikingly similar from $z\sim1$ to the present day, exhibiting a low dispersion of 0.15 dex, and showing little evolution with redshift in the radial logarithmic slope and scatter. They have the running power law shape typical of the NFW-type profiles, and their inner structure, resolved to $3.8\,h^{-1}$ comoving kpc at $z=1$, shows no signs of converging to an asymptotic slope. Our results suggest that this type of profile is already in place at $z>1$ in the highest-mass haloes in the Universe, and that it remains exceptionally robust to merging activity.
Based on the effective field theory (EFT) of nonsingular cosmologies, we build a stable model, without the ghost and gradient instabilities, of bounce inflation (inflation is preceded by a cosmological bounce). We perform a full simulation for the evolution of scalar perturbation, and find that the perturbation spectrum has a large-scale suppression (as expected), which is consistent with the power deficit of the cosmic microwave background (CMB) TT-spectrum at low multipoles, but unexpectedly, it also shows itself one marked lower valley, which actually provides a better fit to the dip at multipole $l\sim 20$. The depth of valley is relevant with the physics around the bounce scale, which is model-dependent.
The possibility that a relevant fraction of the dark matter might be comprised of Primordial Black Holes (PBHs) has been seriously reconsidered after LIGO's detection of a $\sim 30 M_{\odot}$ binary black holes merger. Despite the strong interest in the model, there is a lack of studies on possible cosmological implications and effects on cosmological parameters inference. We investigate correlations with the other standard cosmological parameters using cosmic microwave background observations, finding significant degeneracies, especially with the tilt of the primordial power spectrum and the sound horizon at radiation drag. However, these degeneracies can be greatly reduced with the inclusion of small scale polarization data. We also explore if PBHs as dark matter in simple extensions of the standard $\Lambda$CDM cosmological model induces extra degeneracies, especially between the additional parameters and the PBH's ones. Finally, we present cosmic microwave background constraints on the fraction of dark matter in PBHs, not only for monochromatic PBH mass distributions but also for popular extended mass distributions. Our results show that extended mass distribution's constraints are tighter, but also that a considerable amount of constraining power comes from the high-$\ell$ polarization data. Moreover, we constrain the shape of such mass distributions in terms of the correspondent constraints on the PBH mass fraction.
The model in which Primordial Black Holes (PBHs) constitute a non-negligible fraction of the dark matter has (re)gained popularity after the first detections of binary black hole mergers. Most of the observational constraints to date have been derived assuming a single mass for all the PBHs, although some more recent works tried to generalize constraints to the case of extended mass functions. Here we derive a general methodology to obtain constraints for any PBH Extended Mass Distribution (EMD) and any observables in the desired mass range. Starting from those obtained for a monochromatic distribution, we convert them into constraints for EMDs by using an equivalent, effective mass $M_{\rm eq}$ that depends on the specific observable. We highlight how limits of validity of the PBH modelling affect the EMD parameter space. Finally, we present converted constraints on the total abundance of PBH from microlensing, stellar distribution in ultra-faint dwarf galaxies and CMB accretion for Lognormal and Power Law mass distributions, finding that EMD constraints are generally stronger than monochromatic ones.
Loop quantum cosmology (LQC) provides a resolution of the classical big bang singularity in the deep Planck era. The evolution, prior to the usual slow-roll inflation, naturally generates excited states at the onset of the slow-roll inflation. It is expected that these quantum gravitational effects could leave its fingerprints on the primordial perturbation spectrum and non-Gaussianity, and lead to some observational evidences in the cosmic microwave background (CMB). While the impact of the quantum effects on the primordial perturbation spectrum has been already studied and constrained by current data, in this paper we continue studying such effects on the non-Gaussianity of the primordial curvature perturbations. In this paper, we present detailed and analytical calculations of the non-Gaussianity and show explicitly that the corrections due to quantum effects are in the same magnitude of the slow-roll parameters in the observable scales and thus are well within current observational constraints. Despite this, we show that the non-Gaussianity in the squeezed limit can be enhanced at superhorizon scales and further, these effects may yield a large statistical anisotropy on the power spectrum through the Erickcek-Kamionkowski-Carroll mechanism.
This paper is the first of a series of papers constraining cosmological parameters with weak lensing peak statistics using $\sim 450~\rm deg^2$ of imaging data from the Kilo Degree Survey (KiDS-450). We measure high signal-to-noise ratio (SNR: $\nu$) weak lensing convergence peaks in the range of $3<\nu<5$, and employ theoretical models to derive expected values. These models are validated using a suite of simulations. We take into account two major systematic effects, the boost factor and the effect of baryons on the mass-concentration relation of dark matter haloes. In addition, we investigate the impacts of other potential astrophysical systematics including the projection effects of large scale structures, intrinsic galaxy alignments, as well as residual measurement uncertainties in the shear and redshift calibration. Assuming a flat $\Lambda$CDM model, we find constraints for $S_{\rm 8}=\sigma_{\rm 8}(\Omega_{\rm m}/0.3)^{0.5}=0.746^{+0.046}_{-0.107}$ according to the degeneracy direction of the cosmic shear analysis and $\Sigma_{\rm 8}=\sigma_{\rm 8}(\Omega_{\rm m}/0.3)^{0.38}=0.696^{+0.048}_{-0.050}$ based on the derived degeneracy direction of our high-SNR peak statistics. The difference between the power index of $S_{\rm 8}$ and in $\Sigma_{\rm 8}$ indicates that combining the two probes has the potential to break the degeneracy in $\sigma_{\rm 8}$ and $\Omega_{\rm m}$. Our results are consistent with the cosmic shear tomographic correlation analysis of the same dataset and $\sim 2\sigma$ lower than the Planck 2016 results.
We study the statistics of peaks in a weak lensing reconstructed mass map of the first 450 square degrees of the Kilo Degree Survey. The map is computed with aperture masses directly applied to the shear field with an NFW-like compensated filter. We compare the peak statistics in the observations with that of simulations for various cosmologies to constrain the cosmological parameter $S_8 = \sigma_8 \sqrt{\Omega_{\rm m}/0.3}$, which probes the ($\Omega_{\rm m}, \sigma_8$) plane perpendicularly to its main degeneracy. We estimate $S_8=0.750\pm0.059$, using peaks in the signal-to-noise range $0 \leq {\rm S/N} \leq 4$, and accounting for various systematics, such as multiplicative shear bias, mean redshift bias, baryon feedback, intrinsic alignment, and shear-position coupling. These constraints are $\sim25\%$ tighter than the constraints from the high significance peaks alone ($3 \leq {\rm S/N} \leq 4$) which typically trace single-massive halos. This demonstrates the gain of information from low-S/N peaks which correspond to the projection of several small-mass halos along the line-of-sight. Our results are in good agreement with the tomographic shear two-point correlation function measurement in KiDS-450. Combining shear peaks with non-tomographic measurements of the shear two-point correlation functions yields an $\sim20\%$ improvement in the uncertainty on $S_8$ compared to the shear two-point correlation functions alone, highlighting the great potential of peaks as a cosmological probe.
The status of searches for possible variation in the constants of nature from astronomical observation of molecules is reviewed, focusing on the dimensionless constant representing the proton-electron mass ratio $\mu=m_p/m_e$. The optical detection of H$_2$ and CO molecules with large ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as the detection of H$_2$ with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope is discussed in the context of varying constants, and in connection to different theoretical scenarios. Radio astronomy provides an alternative search strategy bearing the advantage that molecules as NH$_3$ (ammonia) and CH$_3$OH (methanol) can be used, which are much more sensitive to a varying $\mu$ than diatomic molecules. Current constraints are $|\Delta\mu/\mu| < 5 \times 10^{-6}$ for redshift $z=2.0-4.2$, corresponding to look-back times of 10-12.5 Gyrs, and $|\Delta\mu/\mu| < 1.5 \times 10^{-7}$ for $z=0.88$, corresponding to half the age of the Universe (both at 3$\sigma$ statistical significance). Existing bottlenecks and prospects for future improvement with novel instrumentation are discussed.
In the last decades, a cosmological model that fits observations through a vast range of scales emerged. It goes under the name of ${\Lambda}$CDM. However, there are still challenging questions that remain unanswered by this model, such as what causes the observed accelerated expansion of the universe, and many alternatives have been proposed. This thesis concerns an approach to test such models known as "Effective Theory of Dark Energy" . It applies to all models where general relativity is modified by adding a single scalar degree of freedom, called "scalar-tensor theories". In Chapter 1 I summarise the most general class of such theories currently known, called "Degenerate higher-Order Scalar-Tensor" (DHOST) theories. In Chapter 2, I introduce the effective theory of dark energy. The inclusion of a general coupling between matter and the gravitational sector is the subject of Chapter 3. Chapter 4 analyses in details the stability of different classes of theories. Notably, I show that the most general class of theories free from instabilities reduces to the so-called Horndeski and beyond-Horndeski theories, up to a non minimal coupling to matter. Another goal of the thesis is to study the observable effects of deviations from ${\Lambda}$CDM. In Chapter 5, I consider the possibility of an interaction between dark matter and dark energy and I analyse the constraining power of future surveys on the free parameters of the theory. Chapter 6 focuses on the observational effects of theories where a kinetic mixing between matter and the scalar field exists. This gives a peculiar and potentially observable effect, namely the weakening of gravity at large scale structure scales.
We compare Higgs inflation in the metric and Palatini formulations of general relativity, with loop corrections are treated in a simple approximation. We consider Higgs inflation on the plateau, at a critical point, at a hilltop and in a false vacuum. In the last case there are only minor differences. Otherwise we find that in the Palatini formulation the tensor-to-scalar ratio is consistently suppressed, spanning the range $1\times10^{-13}<r<7\times10^{-5}$, compared to the metric case result $2\times10^{-5}<r<0.2$. Even when the values of $n_s$ and $r$ overlap, the running and running of the running are different in the two formulations. Therefore, if Higgs is the inflaton, inflationary observables can be used to distinguish between different gravitational degrees of freedom, in this case to determine whether the connection is an independent variable. Non-detection of $r$ in foreseeable future observations would not rule out Higgs inflation, only its metric variant. We conclude that in order to fix the theory of Higgs inflation, not only the particle physics UV completion but also the gravitational degrees of freedom have to be explicated.
We study the asymmetry in the two-point cross-correlation function of two populations of galaxies focusing in particular on the relativistic effects that include the gravitational redshift. We derive the cross-correlation function on small and large scales using two different approaches: General Relativistic and Newtonian perturbation theory. Following recent work by Bonvin et al., Gaztanaga et al. and Croft, we calculate the dipole and the shell estimator with the two procedures and we compare our results. We find that while General Relativistic Perturbation Theory (GRPT) is able to make predictions of relativistic effects on very large, obviously linear scales (r > 50 Mpc/h), the presence of non-linearities physically occurring on much smaller scales (down to those describing galactic potential wells) can strongly affect the asymmetry estimators. These can lead to cancellations of the relativistic terms, and sign changes in the estimators on scales up to r ~ 50 Mpc/h. On the other hand, with an appropriate non-linear gravitational potential, the results obtained using Newtonian theory can successfully describe the asymmetry on smaller, non-linear scales (r < 20 Mpc/h) where gravitational redshift is the dominant term. On larger scales the asymmetry is much smaller in magnitude, and measurement is not within reach of current observations. This is in agreement with the observational results obtained by Gaztnaga et al. and the first detection of relativistic effects (on (r < 20 Mpc/h) scales) by Alam et al.
General relativistic effects have long been predicted to subtly influence the observed large-scale structure of the universe. The current generation of galaxy redshift surveys have reached a size where detection of such effects is becoming feasible. In this paper, we report the first detection of the redshift asymmetry from the cross-correlation function of two galaxy populations which is consistent with relativistic effects. The dataset is taken from the Sloan Digital Sky Survey DR12 CMASS galaxy sample, and we detect the asymmetry at the $2.7\sigma$ level by applying a shell-averaged estimator to the cross-correlation function. Our measurement dominates at scales around $10$ h$^{-1}$Mpc, larger than those over which the gravitational redshift profile has been recently measured in galaxy clusters, but smaller than scales for which linear perturbation theory is likely to be accurate. The detection significance varies by 0.5$\sigma$ with the details of our measurement and tests for systematic effects. We have also devised two null tests to check for various survey systematics and show that both results are consistent with the null hypothesis. We measure the dipole moment of the cross-correlation function, and from this the asymmetry is also detected, at the $2.8 \sigma$ level. The amplitude and scale-dependence of the clustering asymmetries are approximately consistent with the expectations of General Relativity and a biased galaxy population, within large uncertainties. We explore theoretical predictions using numerical simulations in a companion paper.
In a galaxy redshift survey the objects to be targeted for spectra are selected from a photometrically observed sample. The observed magnitudes and colours of galaxies in this parent sample will be affected by their peculiar velocities, through relativistic Doppler and relativistic beaming effects. In this paper we compute the resulting expected changes in galaxy photometry. The magnitudes of the relativistic effects are a function of redshift, stellar mass, galaxy velocity and velocity direction. We focus on the CMASS sample from the Sloan Digital Sky Survey (SDSS), Baryon Oscillation Spectroscopic Survey (BOSS), which is selected on the basis of colour and magnitude. We find that 0.10\% of the sample ($\sim 585$ galaxies) has been scattered into the targeted region of colour-magnitude space by relativistic effects, and conversely 0.09\% of the sample ($\sim 532$ galaxies) has been scattered out. Observational consequences of these effects include an asymmetry in clustering statistics, which we explore in a companion paper. Here we compute a set of weights which can be used to remove the effect of modulations introduced into the density field inferred from a galaxy sample. We conclude by investigating the possible effects of these relativistic modulation on large scale clustering of the galaxy sample.
Large redshift surveys of galaxies and clusters are providing the first opportunities to search for distortions in the observed pattern of large-scale structure due to such effects as gravitational redshift. We focus on non-linear scales and apply a quasi-Newtonian approach using N-body simulations to predict the small asymmetries in the cross-correlation function of two galaxy different populations. Following recent work by Bonvin et al., Zhao and Peacock and Kaiser on galaxy clusters, we include effects which enter at the same order as gravitational redshift: the transverse Doppler effect, light-cone effects, relativistic beaming, luminosity distance perturbation and wide-angle effects. We find that all these effects cause asymmetries in the cross-correlation functions. Quantifying these asymmetries, we find that the total effect is dominated by the gravitational redshift and luminosity distance perturbation at small and large scales, respectively. By adding additional subresolution modelling of galaxy structure to the large-scale structure information, we find that the signal is significantly increased, indicating that structure on the smallest scales is important and should be included. We report on comparison of our simulation results with measurements from the SDSS/BOSS galaxy redshift survey in a companion paper.
LIGO-Virgo collaboration has found black holes as heavy as $M \sim 30M_\odot$ through the detections of the gravitational waves emitted during their mergers. Primordial black holes (PBHs) produced by inflation could be an origin of such events. While it is tempting to presume that these PBHs constitute all Dark Matter (DM), there exists a number of constraints for PBHs with $\mathcal{O} (10) M_\odot$ which contradict with the idea of PBHs as all DM. Also, it is known that weakly interacting massive particle (WIMP) that is a common DM candidate is almost impossible to coexist with PBHs. These observations motivate us to pursue another candidate of DM. In this paper, we assume that the string axion solving the strong CP problem makes up all DM, and discuss the coexistence of string axion DM and inflationary PBHs for LIGO events.
Low-scale leptogenesis provides an economic and testable description of the origin of the baryon asymmetry of the Universe. In this scenario, the baryon asymmetry of the Universe is reprocessed from the lepton asymmetry by electroweak sphaleron processes. Provided that sphalerons are fast enough to maintain equilibrium, the values of the baryon and lepton asymmetries are related to each other. Usually, this relation is used to find the value of the baryon asymmetry at the time of the sphaleron freeze-out. To put in other words, the formula which is valid only when the sphalerons are fast, is applied at the moment when they are actually switched off. In this paper, we examine the validity of such a treatment. To this end, we solve the full system of kinetic equations for low-scale leptogenesis. This system includes equations describing the production of the lepton asymmetry in oscillations of right-handed neutrinos, as well as a separate kinetic equation for the baryon asymmetry. We show that for some values of the model parameters, the corrections to the standard approach are sizeable. We also present a feasible improvement to the ordinary procedure, which accounts for these corrections.
Axion-like particles are promising candidates to make up the dark matter of the universe, but it is challenging to design experiments that can detect them over their entire allowed mass range. Dark matter in general, and in particular axion-like particles and hidden photons, can be as light as roughly $10^{-22} \;\rm{eV}$ ($\sim 10^{-8} \;\rm{Hz}$), with astrophysical anomalies providing motivation for the lightest masses ("fuzzy dark matter"). We propose experimental techniques for direct detection of axion-like dark matter in the mass range from roughly $10^{-13} \;\rm{eV}$ ($\sim 10^2 \;\rm{Hz}$) down to the lowest possible masses. In this range, these axion-like particles act as a time-oscillating magnetic field coupling only to spin, inducing effects such as a time-oscillating torque and periodic variations in the spin-precession frequency with the frequency and direction set by fundamental physics. We show how these signals can be measured using existing experimental technology, including torsion pendulums, atomic magnetometers, and atom interferometry. These experiments demonstrate a strong discovery capability, with future iterations of these experiments capable of pushing several orders of magnitude past current astrophysical bounds.
Links to: arXiv, form interface, find, astro-ph, recent, 1709, contact, help (Access key information)
Both simulations and observations have confirmed that the spin of haloes/galaxies is correlated with the large scale structure (LSS) with a mass dependence such that the spin of low-mass haloes/galaxies tend to be parallel with the LSS, while that of massive haloes/galaxies tend to be perpendicular with the LSS. It is still unclear how this mass dependence is built up over time. We use N-body simulations to trace the evolution of the halo spin-LSS correlation and find that at early times the spin of all halo progenitors is parallel with the LSS. As time goes on, mass collapsing around massive halo is more isotropic, especially the recent mass accretion along the slowest collapsing direction is significant and it brings the halo spin to be perpendicular with the LSS. Adopting the $fractional$ $anisotropy$ (FA) parameter to describe the degree of anisotropy of the large-scale environment, we find that the spin-LSS correlation is a strong function of the environment such that a higher FA (more anisotropic environment) leads to an aligned signal, and a lower anisotropy leads to a misaligned signal. In general, our results show that the spin-LSS correlation is a combined consequence of mass flow and halo growth within the cosmic web. Our predicted environmental dependence between spin and large-scale structure can be further tested using galaxy surveys.
We investigate the possibility of performing cosmological studies in the redshift range $2.5<z<5$ through suitable extensions of existing and upcoming radio-telescopes like CHIME, HIRAX and FAST. We use the Fisher matrix technique to forecast the bounds that those instruments can place on the growth rate, the Alcock-Paczynski parameters, the sum of the neutrino masses and the number of relativistic degrees of freedom at decoupling, $N_{\rm eff}$. We point out that quantities that depend on the amplitude of the 21cm power spectrum, like $f\sigma_8$, are completely degenerate with $\Omega_{\rm HI}$ and $b_{\rm HI}$, and propose several strategies to independently constraint them through cross-correlations with other probes. Assuming $5\%$ priors on $\Omega_{\rm HI}$ and $b_{\rm HI}$, $k_{\rm max}=0.2~h{\rm Mpc}^{-1}$ and the primary beam wedge, we find that a HIRAX extension can constrain, within bins of $\Delta z=0.1$: 1) the value of $f\sigma_8$ at $\simeq4\%$, 2) the value of $D_A$ and $H$ at $\simeq1\%$. In combination with data from Euclid-like galaxy surveys and CMB S4, the sum of the neutrino masses can be constrained with an error equal to $23$ meV ($1\sigma$), while $N_{\rm eff}$ can be constrained within 0.02 ($1\sigma$). We derive similar constraints for the extensions of the other instruments. We study in detail the dependence of our results on the instrument, amplitude of the HI bias, the foreground wedge coverage, the nonlinear scale used in the analysis, uncertainties in the theoretical modeling and the priors on $b_{\rm HI}$ and $\Omega_{\rm HI}$. We conclude that 21cm intensity mapping surveys operating in this redshift range can provide extremely competitive constraints on key cosmological parameters.
Polarized Galactic foregrounds are one of the primary sources of systematic error in measurements of the B-mode polarization of the Cosmic Microwave Background (CMB). Experiments are becoming increasingly sensitive to complexities in the foreground frequency spectra that are not captured by standard parametric models, potentially affecting our ability to efficiently separate out these components. Employing a suite of dust models encompassing a variety of physical effects, we simulate observations of a future seven-band CMB experiment to assess the impact of these complexities on parametric component separation. We identify configurations of frequency bands that minimize the `model errors' caused by fitting simple parametric models to more complex `true' foreground spectra, which bias the inferred CMB signal. We find that: (a) fits employing a simple two parameter modified blackbody (MBB) dust model tend to produce significant bias in the recovered polarized CMB signal in the presence of physically realistic dust foregrounds; (b) generalized MBB models with three additional parameters reduce this bias in most cases, but non-negligible biases can remain, and can be hard to detect; and (c) line of sight effects, which give rise to frequency decorrelation, and the presence of iron grains are the most problematic complexities in the dust emission for recovering the true CMB signal. More sophisticated simulations will be needed to demonstrate that future CMB experiments can successfully mitigate these more physically realistic dust foregrounds.
Ultra-light axions have sparked attention because their tiny mass $m\sim 10^{-22}$ eV, which leads to a Kiloparsec-scale de Broglie wavelength comparable to the size of dwarf galaxy, could alleviate the so-called small-scale crisis of massive cold dark matter (CDM) candidates.However, recent analyses of the Lyman-$\alpha$ forest power spectrum set a tight lower bound on their mass of $m\gtrsim 10^{-21}$ eV which makes them much less relevant from an astrophysical point of view. An important caveat to these numerical studies is that they do not take into account attractive self-interactions among ultra-light axions, which can counteract the quantum "pressure" induced by the strong delocalization of the particles. In this work, we show that even a tiny attractive interaction among ultra-light axions can have a significant impact on the stability of cosmic structures at low redshift. After a brief review of known results about solitons in the absence of gravity, we discuss the stability of filamentary and pancake-like solutions when quantum pressure, attractive interactions and gravity are present. The analysis based on one degree of freedom, namely the breathing mode, reveals that pancakes are stable, while filaments are unstable if the mass per unit length is larger than a critical value. However, we show that pancakes are unstable against transverse perturbations. We expect this to be true for halos and filaments as well. Finally, we also assess whether these instabilities can leave a detectable signature in the Lyman-$\alpha$ forest. We find that unstable filaments could be seen as absorption lines with column densities of neutral hydrogen $N_\text{HI}\lesssim 10^{17}$ cm$^{-2}$ even for an axion decay constant as large as $f\lesssim 10^{16}$ GeV. We hope our work motivates future numerical studies of the impact of axion self-interactions on cosmic structure formation.
The dispersion measure (DM) of high-redshift $(z \gtrsim 6)$ transient objects such as Fast Radio Bursts can be a powerful tool to probe the intergalactic medium during the Epoch of Reionization. In this paper, we study the variance of the DMs of objects with the same redshift as a potential probe of the size distribution of ionized bubbles. We calculate the DM variance with a simple model with randomly-distributed spherical bubbles. It is found that the DM variance reflects the characteristics of the probability distribution of the bubble size. We find the variance can be measured precisely enough to obtain the information on the typical size with a few hundred sources at a single redshift.
We present quantities which characterize the sensitivity of gravitational-wave observatories to sources at cosmological distances. In particular, we introduce and generalize the horizon, range, response, and reach distances. These quantities incorporate a number of important effects, including cosmologically well-defined distances and volumes, cosmological redshift, cosmological time dilation, and rate density evolution. In addition, these quantities incorporate unique aspects of gravitational wave detectors, such as the variable sky sensitivity of the detectors and the scaling of the sensitivity with inverse distance. An online calculator (this http URL) and python notebook (https://github.com/hsinyuc/distancetool) to determine GW distances are available. We provide answers to the question: "How far can gravitational-wave detectors hear?"
We introduce a $\textit{frequency-dependent}$ Doppler and aberration
transformation kernel for the harmonic multipoles of a general cosmological
observable with spin weight $s$, Doppler weight $d$ and arbitrary frequency
spectrum. In the context of Cosmic Microwave Background (CMB) studies, the
frequency-dependent formalism allows to correct for the motion-induced
aberration and Doppler effects on individual frequency maps with different
masks. It also permits to deboost background radiations with non-blackbody
frequency spectra, like extragalactic foregrounds and CMB spectra with
primordial spectral distortions. The formalism can also be used to correct
individual E and B polarization modes and account for motion-induced E/B mixing
of polarized observables with $d\neq1$ at different frequencies.
We apply the generalized aberration kernel on polarized and unpolarized CMB
specific intensity at 100 and 217 GHz and show that the motion-induced effects
typically increase with the frequency of observation. In all-sky CMB
experiments, the frequency-dependence of the motion-induced effects for a
blackbody spectrum are overall negligible. However in a cut-sky analysis,
ignoring the frequency dependence can lead to percent level error in the
polarized and unpolarized power spectra over all angular scales. In the
specific cut-sky used in our analysis ($b > 45^\circ, f_\text{sky}\simeq14\%$),
and for the dipole-inferred velocity $\beta=0.00123$ typically attributed to
our peculiar motion, the Doppler and aberration effects can change polarized
and unpolarized power spectra of specific intensity in the CMB rest frame by
$1-2\%$, but we find the polarization cross-leakage between E and B modes to be
negligible.
The cosmological constant problem has become one of the most important ones in modern cosmology. In this paper, we try to construct a model that can avoid the cosmological constant problem and have the potential to explain the apparent late-time accelerating expansion of the universe in both luminosity distance and angular diameter distance measurement channels. In our model, the core is to modify the relation between cosmological redshift and scale factor for photons. We point out three ways to test our hypothesis: the supernova time dilation; the gravitational waves and its electromagnetic counterparts emitted by the binary neutron star systems; and the Sandage--Loeb effect. All of this method is feasible now or in the near future.
We study PTF11mnb, a He-poor supernova (SN) whose pre-peak light curves (LCs) resemble those of SN 2005bf, a peculiar double-peaked stripped-envelope (SE) SN. LCs, colors and spectral properties are compared to those of SN 2005bf and normal SE SNe. A bolometric LC is built and modeled with the SNEC hydrodynamical code explosion of a MESA progenitor star, as well as with semi-analytic models. The LC of PTF11mnb turns out to be similar to that of SN 2005bf until $\sim$50 d, when the main (secondary) peaks occur at $-18.5$ mag. The early peak occurs at $\sim$20 d, and is about 1.0 mag fainter. After the main peak, the decline rate of PTF11mnb is remarkably slower than that of SN 2005bf, and it traces the $^{56}$Co decay rate. The spectra of PTF11mnb reveal no traces of He unlike in the case of SN Ib 2005bf. The bolometric LC is well reproduced by the explosion of a massive ($M_{ej} =$ 7.8 $M_{\odot}$), He-poor star with a double-peaked $^{56}$Ni distribution, a total $^{56}$Ni mass of 0.59 $M_{\odot}$ and an explosion energy of 2.2$\times$10$^{51}$ erg. Alternatively, a normal SN Ib/c explosion [M($^{56}$Ni)$=$0.11 $M_{\odot}$, $E_{K}$ = 0.2$\times$10$^{51}$ erg, $M_{ej} =$ 1 $M_{\odot}$] can power the first peak while a magnetar ($B$=5.0$\times$10$^{14}$ G, $P=18.1$ ms) provides energy for the main peak. The early $g$-band LC implies a radius of at least 30 $R_{\odot}$. If PTF11mnb arose from a massive He-poor star characterized by a double-peaked $^{56}$Ni distribution, the ejecta mass and the absence of He imply a large ZAMS mass ($\sim85 M_{\odot}$) for the progenitor, which most likely was a Wolf-Rayet star, surrounded by an extended envelope formed either by a pre-SN eruption or due to a binary configuration. Alternatively, PTF11mnb could be powered by a normal SE SN during the first peak and by a magnetar afterwards.
We consider five dimensional conformal gravity theory which describes an anisotropic extra dimension. Reducing the theory to four dimensions yields Brans-Dicke theory with a potential and a hidden parameter $z$ which implements the anisotropy between the four dimensional spacetime and the extra dimension. We find that a range of value of the parameter $z$ can address the current dark energy density compared to the Planck energy density. Constraining the parameter $z$ and the other cosmological model parameters using the recent observational data consisting of the Hubble parameters, type Ia supernovae, and baryon acoustic oscillations, together with the Planck or WMAP 9-year data of the cosmic microwave background radiation, we find $z>-2.05$ for Planck data and $z>-2.09$ for WMAP 9-year data at 95\% confidence level. We also obtained constraints on the rate of change of the effective Newtonian constant~($G_{\rm eff}$) at present and the variation of $G_{\rm eff}$ since the epoch of recombination to be consistent with observation.
By assumption of existence of some ultra-dense regions in the real cosmic fluid, we try to explain the accelerated expansion in both early and present universe. By use of the leading terms in the \emph{virial expansion} for the equation of state in the FRLW framework, in the form of $\frac{P}{c^2}=\omega\rho+B\rho^2$, we are able to solve the Friedmann equations analytically. Then, we obtain alternative relations for the energy density and scale factor evolution that will coincide with the conventional result in the non-virial limit of cosmic fluid. Also, the model is able to justify extra-acceleration in the very early universe, that is needed for the cosmic inflation. As an important result, the model shows that the three form of matter, radiation, and ultra-dense regions are always existing in the cosmic fluid, and that the universe is always expanding because of the negativity of its net EOS parameter.
Sub-GeV halo dark matter that enters the Sun can potentially scatter off hot solar nuclei and be ejected with a much larger velocity than the incoming one. We derive an expression for the rate and velocity distribution of these reflected particles taking into account the Sun's temperature and opacity and we investigate the prospects of detecting this population. We demonstrate that future detectors could use these energetic reflected particles to probe light dark matter in parameter space that the ordinary halo population cannot access.
We present a simple effective field theory formulation of a general family of single field flux monodromy models for which strong coupling effects at large field values can flatten the potential and activate operators with higher powers of derivatives. These models are radiatively and non-perturbatively stable and can easily sustain $\ga 60$ efolds of inflation. The dynamics combines features of both large field chaotic inflation and $k$-inflation, both of which can suppress the tensor amplitude. Reducing the tensor-scalar ratio below the observational bound $r \lesssim 0.1$ while keeping the scalar spectral index $n_s$ within experimental bounds either yields equilateral nongaussianity $f_{NL}^{eq} \simeq {\cal O}(1)$, close to the current observational bounds, or ultimately gives very small $r$.
We present a statistical characterization of the $\gamma$-ray emission from the four \emph{Fermi}-LAT sources: FR I radio galaxy NGC 1275, BL Lac Mrk 421, FSRQs B2 1520+31 and PKS 1510-089 detected almost continuously over a time integration of 3-days between August 2008 - October 2015. The observed flux variation is large, spanning $\gtrsim 2$ orders of magnitude between the extremes except for Mrk~421. We compute the flux distributions and compare with Gaussian and lognormal ones. We find that the 3 blazars have distribution consistent with a lognormal, suggesting that the variability is of a non-linear, multiplicative nature. This is further supported by the computation of the flux-rms relation, which is observed to be linear for the 3 blazars. However, for NGC 1275, the distribution does not seem to be represented either by a lognormal or a Gaussian, while its flux-rms relation is still found to be linear. We also compute the power spectra, which suggest the presence of a break, but are consistent with typical scale-free power-law shot noise. The results are broadly consistent with the statistical properties of the magnetic reconnection powered minijets-in-a-jet model. We discuss other possible scenarios and implications of these observations on jet processes and connections with the central engine.
We study the dynamical structure of a bimodal galaxy cluster Abell 3653 at z=0.1089 by using combined optical and X-ray data. Observations include archival data from Anglo-Australian Telescope and X-ray observatories of XMM-Newton and Chandra. We draw a global picture for A3653 using galaxy density, X-ray luminosity and temperature maps. Galaxy distribution has a regular morphological shape at the 3 Mpc size. Galaxy density map shows an elongation EW direction, which perfectly aligns with the extended diffuse X-ray emission. We detect two dominant grouping around two brightest cluster galaxies (BCGs). The BCG1 (z=0.1099) can be associated with the main cluster A3653E, and a foreground subcluster A3563W concentrated at the BCG2 (z=0.1075). Both X-ray peaks are dislocated from BCGs by ($\sim$35 kpc), which suggest an ongoing merger process. We measure the subclusters' gas temperatures 4.67 and 3.66 keV, respectively. Two-body dynamical analysis shows that A3653E & A3653W are very likely (93.5% probability) gravitationally bound. The highly favoured scenario suggests that two subclusters with the mass ratio of 1.4 are colliding close to the plane of sky ($\alpha$=17$^\circ$.61) with 2400 km $s^{-1}$, and will undergo core passage in 380 Myr. Temperature map also significantly shows a shock-heated gas (6.16 keV) in between the subclusters, which confirms the supersonic infalling scenario.
In an effort to search for Ly$\alpha$ emission from circum- and intergalactic gas on scales of hundreds of kpc around $z\sim3$ quasars, and thus characterise the physical properties of the gas in emission, we have initiated an extensive fast-survey with the Multi Unit Spectroscopic Explorer (MUSE): Quasar Snapshot Observations with MUse: Search for Extended Ultraviolet eMission (QSO MUSEUM). In this work, we report the discovery of an enormous Ly$\alpha$ nebula (ELAN) around the quasar SDSS~J102009.99+104002.7 at $z=3.164$, which we followed-up with deeper MUSE observations. This ELAN spans $\sim297$ projected kpc, has an average Ly$\alpha$ surface brightness ${\rm SB}_{\rm Ly\alpha}\sim 6.04\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ (within the $2\sigma$ isophote), and is associated with an additional four, previously unknown embedded sources: two Ly$\alpha$ emitters and two faint active galactic nuclei (one Type-1 and one Type-2 quasar). By mapping at high significance the line-of-sight velocity in the entirety of the observed structure, we unveiled a large-scale coherent rotation-like pattern spanning $\sim300$ km s$^{-1}$ with a velocity dispersion of $<270$ km s$^{-1}$, which we interpret as a signature of the inspiraling accretion of substructures within the quasar's host halo. Future multiwavelength data will complement our MUSE observations, and are definitely needed to fully characterise such a complex system. None the less, our observations reveal the potential of new sensitive integral-field spectrographs to characterise the dynamical state of diffuse gas on large scales in the young Universe, and thereby witness the assembly of galaxies.
Core collapse supernova (CCSN) rates suffer from large uncertainties as many CCSNe exploding in regions of bright background emission and significant dust extinction remain unobserved. Such a shortfall is particularly prominent in luminous infrared galaxies (LIRGs), which have high star formation (and thus CCSN) rates and host bright and crowded nuclear regions, where large extinctions and reduced search detection efficiency likely lead to a significant fraction of CCSNe remaining undiscovered. We present the first results of project SUNBIRD (Supernovae UNmasked By Infra-Red Detection), where we aim to uncover CCSNe that otherwise would remain hidden in the complex nuclear regions of LIRGs, and in this way improve the constraints on the fraction that is missed by optical seeing-limited surveys. We observe in the near-infrared 2.15 {\mu}m $K_s$-band, which is less affected by dust extinction compared to the optical, using the multi-conjugate adaptive optics imager GeMS/GSAOI on Gemini South, allowing us to achieve a spatial resolution that lets us probe close in to the nuclear regions. During our pilot program and subsequent first full year we have discovered three CCSNe and one candidate with projected nuclear offsets as small as 200 pc. When compared to the total sample of LIRG CCSNe discovered in the near-IR and optical, we show that our method is singularly effective in uncovering CCSNe in nuclear regions and we conclude that the majority of CCSNe exploding in LIRGs are not detected as a result of dust obscuration and poor spatial resolution.
Many galaxy clusters have giant halos of non-thermal radio emission, indicating the presence of relativistic electrons in the clusters. Relativistic protons may also be accelerated by merger and/or accretion shocks in galaxy clusters. These cosmic-ray (CR) protons are expected to produce gamma-rays through inelastic collisions with thermal gas of the intra-cluster medium. Despite of intense efforts in searching for high-energy gamma-ray emission from galaxy clusters, conclusive evidence is still missing so far. Here we report the discovery of $\ge100$ MeV gamma-rays from the Coma cluster at a confidence level of $\sim6 \sigma$ with the {\it Fermi} Large Area Telescope (LAT). The result is obtained with the unbinned likelihood analysis of the nine years of {\it Fermi}-LAT Pass 8 data. The gamma-ray emission shows an extended spatial morphology roughly coincident with the giant radio halo, with an apparent excess at the southwest of the cluster. The integral energy flux in the energy range of 0.1-300 GeV is about $3\times 10^{-12}{\rm \ erg\ cm^{-2}\ s^{-1}}$. The spectrum of the gamma-ray emission is soft with a photon index of $\simeq-2.7$. Interpreting the gamma-ray emission as arising from CR proton interaction, we find that the volume-averaged value of the CR to thermal pressure ratio in the Coma cluster is about $\sim 2\%$. Our results show that galaxy clusters are a new type of GeV gamma-ray sources, and they are probably also giant reservoirs of CR protons.
We study a gauged $B-L$ extension of the standard model where the new fermions with fractional $B-L$ charges that play the role of keeping the model anomaly free can also explain the origin of neutrino mass at one loop level as well as dark matter. We discuss two different versions of the model to realise fermion and scalar dark matter, both of which guarantee the dark matter stability by a remnant discrete symmetry to which $U(1)_{B-L}$ gauge symmetry gets spontaneously broken down to. Apart from giving rise to the observed neutrino mass and dark matter abundance, the model also has tantalising signatures at variety of experiments operating at cosmic, intensity and energy frontiers, particularly direct and indirect detection experiments of dark matter, rare decay experiments looking for charged lepton flavour violation as well as collider experiments. The model also predicts vanishing lightest neutrino mass that can be tested at experiments sensitive to the absolute neutrino mass scale.
Annihilating dark matter particles in nearby subhalos could generate potentially observable fluxes of gamma rays, unaccompanied by emission at other wavelengths. Furthermore, this gamma-ray emission is expected to be spatially extended, providing us with a powerful way to discriminate dark matter subhalos from other astrophysical gamma-ray sources. Fermi has detected two dark matter subhalo candidates which exhibit a statistically significant degree of spatial extension (3FGL J2212.5+0703 and 3FGL J1924.8-1034). It has been argued that the most likely non-dark matter interpretation of these observations is that they are each in fact multiple nearby point sources, too close to one another on the sky to be individually resolved. In this study, we consider the ability of next generation gamma-ray telescopes to spatially resolve the gamma-ray emission from subhalo candidates, focusing on the proposed e-ASTROGAM mission. We find that such an instrument could significantly clarify the nature of Fermi's dark matter subhalo candidates, and provide an unprecedented level of sensitivity to the presence of annihilating dark matter in nearby subhalos.
Links to: arXiv, form interface, find, astro-ph, recent, 1709, contact, help (Access key information)
The decay of gravitational potentials in the presence of dark energy leads to an additional, late-time contribution to anisotropies in the cosmic microwave background (CMB) at large angular scales. The imprint of this so-called Integrated Sachs-Wolfe (ISW) effect to the CMB angular power spectrum has been detected and studied in detail, but reconstructing its spatial contributions to the CMB $\textit{map}$, which would offer the tantalizing possibility of separating the early- from the late-time contributions to CMB temperature fluctuations, is more challenging. Here we study the technique for reconstructing the ISW map based on information from galaxy surveys and focus in particular on how its accuracy is impacted by the presence of photometric calibration errors in input galaxy maps, which were previously found to be a dominant contaminant for ISW signal estimation. We find that both including tomographic information from a single survey and using data from multiple, complementary galaxy surveys improve the reconstruction by effectively self-calibrating the estimator against spurious power contributions from calibration errors. A high fidelity reconstruction further requires one to account for the contribution of calibration errors to the observed galaxy power spectrum in the model used to construct the ISW estimator. We find that if the photometric calibration errors in galaxy surveys can be independently controlled at the level required to obtain unbiased dark energy constraints, then it is possible to reconstruct ISW maps with excellent accuracy using a combination of maps from two galaxy surveys with properties similar to Euclid and SPHEREx.
Adding to our previous method for dealing with gravitational modifications at redshift $z\gtrsim3$ through a single parameter, we investigate treatment of lower redshift modifications to linear growth observables. We establish subpercent accurate fits to the redshift space distortion observable $f\sigma_8(a)$ using two parameters binned in redshift, testing the results for modifications with time dependence that rises, falls, is nonmonotonic, is multipeaked, and corresponds to $f(R)$ and braneworld gravity. The residuals are then propagated to cosmological parameter biases for DESI observations, and found to cause a shift in the dark energy joint confidence contour by less than the equivalent of $\sim0.1\sigma$. The proposed 2--3 parameter modified gravity description also can reveal physical characteristics of the underlying theory.
We examine the growth of structure in three different cosmological models with interacting dark matter and vacuum energy. We consider the case of geodesic dark matter with zero sound speed, where the relativistic growing mode in comoving-synchronous gauge coincides with the Newtonian growing mode at first order in $\Lambda$CDM. We study corrections to the linearly growing mode in the presence of interactions and the linear matter growth rate, $f_1$, contrasting this with the velocity divergence, $f_{rsd}\sigma_8$, observed through redshift-space distortions. We then derive second-order density perturbations in these interacting models. We identify the reduced bispectrum that corresponds to the non-linear growth of structure and show how the shape of the bispectrum is altered by energy transfer to or from the vacuum. Thus the bispectrum, or higher-order correlators, might in future be used to identify dark matter interactions.
Primordial black holes (PBHs) form binaries in the radiation dominated era. Once formed, some fraction of them merge within the age of the Universe by gravitational radiation reaction. We investigate the merger rate of the PBH binaries when the PBHs have a distribution of masses around ${\cal O}(10) M_\odot$, which is a generalization of the previous studies where the PBHs are assumed to have the same mass. After deriving a formula for the merger time probability distribution in the PBH mass plane, we evaluate it under two different approximations. We identify a quantity constructed from the mass-distribution of the merger rate density per unit time and volume $\mathcal{R}(m_1,m_2)$, $\alpha = -{(m_1+m_2)}^2 \partial^2 \ln\mathcal{R}/\partial m_1\partial m_2 $, which universally satisfies $0.97 \lesssim \alpha \lesssim 1.05$ for all binary masses independently of the PBH mass function. This result suggests that the measurement of this quantity is useful for testing the PBH scenario.
One application of the Cosmological Gravitational Lensing in General Relativity is the measurement of the Hubble constant H_0 using the time delay Delta t between multiple images of lensed quasars. This method has already been applied, obtaining a value of H_0 compatible with that obtained from the SNe 1A, but non compatible with that obtained studying the anisotropies of the CMB. This difference could be a statistical fluctuation or an indication of new physics beyond the Standard Model of Cosmology, so it desirable to improve the precision of the measurements. At the current technological capabilities it is possible to obtain H_0 to a percent level uncertainty, so a more accurate theoretical model could be necessary in order to increase the precision about the determination of H_0. The actual formula which relates Delta t with H_0 is approximated; in this paper we expose a proposal to go beyond the previous analysis and, within the context of a new model, we obtain a more precise formula than that present in the Literature.
Following the first two annual intensity mapping workshops at Stanford in March 2016 and Johns Hopkins in June 2017, we report on the recent advances in theory, instrumentation and observation that were presented in these meetings and some of the opportunities and challenges that were identified looking forward. With preliminary detections of CO, [CII], Lya and low-redshift 21cm, and a host of experiments set to go online in the next few years, the field is rapidly progressing on all fronts, with great anticipation for a flood of new exciting results. This current snapshot provides an efficient reference for experts in related fields and a useful resource for nonspecialists. We begin by introducing the concept of line-intensity mapping and then discuss the broad array of science goals that will be enabled, ranging from the history of star formation, reionization and galaxy evolution to measuring baryon acoustic oscillations at high redshift and constraining theories of dark matter, modified gravity and dark energy. After reviewing the first detections reported to date, we survey the experimental landscape, presenting the parameters and capabilities of relevant instruments such as COMAP, mmIMe, AIM-CO, CCAT-p, TIME, CONCERTO, CHIME, HIRAX, HERA, STARFIRE, MeerKAT/SKA and SPHEREx. Finally, we describe recent theoretical advances: different approaches to modeling line luminosity functions, several techniques to separate the desired signal from foregrounds, statistical methods to analyze the data, and frameworks to generate realistic intensity map simulations.
Theories of modified gravity where light scalars with non-trivial self-interactions and non-minimal couplings to matter-chameleon and symmetron theories-dynamically suppress deviations from general relativity in the solar system. On other scales, the environmental nature of the screening means that such scalars may be relevant. The highly-nonlinear nature of screening mechanisms means that they evade classical fifth-force searches, and there has been an intense effort towards designing new and novel tests to probe them, both in the laboratory and using astrophysical objects, and by reinterpreting existing datasets. The results of these searches are often presented using different parametrizations, which can make it difficult to compare constraints coming from different probes. The purpose of this review is to summarize the present state-of-the-art searches for screened scalars coupled to matter, and to translate the current bounds into a single parametrization to survey the state of the models. Presently, commonly studied chameleon models are well-constrained but less commonly studied models have large regions of parameter space that are still viable. Symmetron models are constrained well by astrophysical and laboratory tests, but there is a desert separating the two scales where the model is unconstrained. The coupling of chameleons to photons is tightly constrained but the symmetron coupling has yet to be explored. We also summarize the current bounds on $f(R)$ models that exhibit the chameleon mechanism (Hu \& Sawicki models). The simplest of these are well constrained by astrophysical probes, but there are currently few reported bounds for theories with higher powers of $R$. The review ends by discussing the future prospects for constraining screened modified gravity models further using upcoming and planned experiments.
We investigate the large scale matter distribution adopting QSOs as matter tracer. The quasar catalogue based on the SDSS DR7 is used. The void finding algorithm is presented and statistical properties of void sizes and shapes are determined. Number of large voids in the quasar distribution is greater than the number of the same size voids found in the random distribution. The largest voids with diameters exceeding 300 Mpc indicate an existence of comparable size areas of lower than the average matter density. No void-void space correlations have been detected, and no larger scale deviations from the uniform distribution are revealed. The average CMB temperature in the directions of the largest voids is lower than in the surrounding areas by 0.0046 +/- 0.0028 mK. This figure is compared to the amplitude of the expected temperature depletion caused by the Integrated Sachs-Wolfe effect.
We compare Einstein-Boltzmann solvers that include modifications to General Relativity and find that, for a wide range of models and parameters, they agree to a high level of precision. We look at three general purpose codes that primarily model general scalar-tensor theories, three codes that model Jordan-Brans-Dicke (JBD) gravity, a code that models f(R) gravity, a code that models covariant Galileons, a code that models Ho\v{r}ava-Lifschitz gravity and two codes that model non-local models of gravity. Comparing predictions of the angular power spectrum of the cosmic microwave background and the power spectrum of dark matter for a suite of different models, we find agreement at the sub-percent level. This means that this suite of Einstein-Boltzmann solvers is now sufficiently accurate for precision constraints on cosmological and gravitational parameters.
A scenario for gravitational particle creation in a stiff matter dominated flat Friedmann-Robertson-Walker universe is presented. The primary creation of scalar particles is calculated using quantum field theory in curved spacetime and it is found to be strongly dependent on the scalar mass and the expansion parameter of the universe. The particle creation is most effective for a very massive scalar field and large expansion parameter. We apply the results to cosmology and calculate an upper bound for the equilibrium temperature of the secondary particles created by the scalar field decay.
In the presence of a gravitational field decay rates may significantly differ from flat space equivalent. By studying mutually interacting quantum fields the decay rates can be calculated on a given spacetime. This paper presents the calculation of the transition probability for the decay of a massive scalar particle in a stiff matter dominated universe. We find that due to the precence of a gravitational field a finite correction to the transition probability is added which depends inversely on the mass. Moreover the decay rate is smaller and lifetime of the particles is longer compared to flat space. The mass dependence is such that the lifetime of lighter particles is prolonged more compared to heavier particles. This result may be of significance when studying cosmological situations involving stiff matter.
The Minimal Dark Matter framework classifies viable Dark Matter (DM) candidates that are obtained by simply augmenting the Standard Model of particle interactions with a new multiplet, without adding new ad hoc symmetries to make the DM stable. The model has no free parameters and is therefore extremely predictive; moreover, recent studies singled out a Majorana $SU(2)_\text{L}$ quintuplet as the only viable candidate. The model can be constrained by both direct and indirect DM searches, with present time gamma-ray line searches in the Galactic Center being particularly sensitive. It is therefore timely to critically review this paradigm and point out possible generalizations. We propose and explore two distinct directions. One is to lower the cutoff of the model, which was originally fixed at the Planck scale, to allow for decays of the DM quintuplet. We analyze the decay spectrum of this candidate in detail and show that gamma-ray data constrain the cutoff to lie above the GUT scale. Another possibility is to abandon the assumption of DM electric neutrality in favor of absolutely stable, millicharged DM candidates. We explicitly study a few examples, and find that a Dirac $SU(2)_\text{L}$ triplet is the candidate least constrained by indirect searches.
A neutral dark matter (DM) particle with a magnetic dipole moment has a very different direct detection phenomenology with respect to standard candidates. This is due to the peculiar functional form of the differential cross section for scattering with nuclei. Such a candidate could be a bound state of charged particles, as the neutron or an atom, or a fundamental particle coupled to heavier charged states, much like a Dirac neutrino. We analyze here the direct detection signals of DM with magnetic dipole moment, both the recoil rate and its modulation, and show that they are very different from those expected in standard scenarios. For this candidate, contrary to the common lore, the time of maximum signal depends on the recoil energy as well as on the target material. The observation of different modulations by experiments employing different targets would be a strong indication in favor of this type of DM particles.
We present a comprehensive temporal and spectral analysis of the long Swift GRB 120327A afterglow data to investigate the possible causes of the observed early time colour variations. We collected data from various instruments/telescopes in different bands (X-rays, ultra- violet, optical and near-infrared) and determined the shapes of the afterglow early-time light curves. We studied the overall temporal behaviour and the spectral energy distributions from early to late times. The ultra-violet, optical, and near-infrared light curves can be modelled with a single power-law component between 200 and 2e4 s after the burst event. The X-ray light curve shows a canonical steep-shallow-steep behaviour, typical of long gamma-ray bursts. At early times a colour variation is observed in the ultra-violet/optical bands, while at very late times a hint of a re-brightening is visible. The observed early time colour change can be explained as a variation in the intrinsic optical spectral index, rather than an evolution of the optical extinction.
Links to: arXiv, form interface, find, astro-ph, recent, 1709, contact, help (Access key information)
Axions and axion-like particles are a leading model for the dark matter in the Universe; therefore, dark matter halos may be boson stars in the process of collapsing. We examine a class of static boson stars with a non-minimal coupling to gravity. We modify the gravitational density of the boson field to be proportional to an arbitrary power of the modulus of the field, introducing a non-standard coupling. We find a class of solutions very similar to Newtonian polytropic stars that we denote "quantum polytropes." These quantum polytropes are supported by a non-local quantum pressure and follow an equation very similar to the Lane-Emden equation for classical polytropes. Furthermore, we derive a simple condition on the exponent of the non-linear gravitational coupling, $\alpha>8/3$, beyond which the equilibrium solutions are unstable.
We present an impact of coupling between dark matter and a scalar field, which might be responsible for dark energy, on measurements of redshift-space distortions. We point out that, in the presence of conformal and/or disformal coupling, linearized continuity and Euler equations for total matter fluid significantly deviate from the standard ones even in the sub-horizon scales. In such a case, a peculiar velocity of total matter field is determined not only by a logarithmic time derivative of its density perturbation but also by density perturbations for both dark matter and baryon, leading to a large modification of the physical interpretation of observed data obtained by measurements of redshift-space distortions. We reformulate galaxy two-point correlation function in the redshift space based on the modified continuity and Euler equations. We conclude from the resultant formula that the true value of the linear growth rate of large-scale structure cannot be necessarily constrained by single-redshift measurements of the redshift-space distortions, unless one observes the actual time-evolution of structure.
Aims. We use accurate data on distances and radial velocities of galaxies
around the Local Group, as well as around 14 other massive nearby groups, to
estimate their radius of the zero-velocity surface, $R_0$, which separates any
group against the global cosmic expansion.
Methods. Our $R_0$ estimate was based on fitting the data to the velocity
field expected from the spherical infall model, including effects of the
cosmological constant. The reported uncertainties were derived by a Monte Carlo
simulation.
Results. Testing various assumptions about a location of the group
barycentre, we found the optimal estimates of the radius to be
$0.91\pm0.05$~Mpc for the Local Group, and $0.93\pm0.02$~Mpc for a synthetic
group stacked from 14 other groups in the Local Volume. Under the standard
Planck model parameters, these quantities correspond to the total mass of the
group $\sim (1.6\pm0.2) 10^{12} M_{\odot}$. Thus, we are faced with the
paradoxical result that the total mass estimate on the scale of $R_0 \approx
(3- 4) R_{vir}$ is only $~60$% of the virial mass estimate. Anyway, we conclude
that wide outskirts of the nearby groups do not contain a large amount of
hidden mass outside their virial radius.
We study the matter bispectrum of large structure by comparing theoretical models (perturbation theories and halo models) to numerical simulations using shape and amplitude correlators. We show that among the perturbation theories at one loop the effective field theory of large scale structure extends the furthest into the non-linear regime. We analyse the one and two-loop bispectra in the renormalised perturbation theory and we show that there is a significant extension in the range where results are accurate when going to two loops. In the case of the halo model, we show that there are deficiencies in the modelling of the two-halo term at redshifts z>0 that worsen in the past. Based on this observation and on the shapes identified in the halo model, we build a simple `three-shape model' that provides a good fit to N-body simulations on all scales, at both low and high redshifts. We show that this model can be easily extended to local and equilateral primordial non-Gaussianity using the same shapes.
The Cosmic Microwave Background (CMB) Polarization plays an important role in current cosmological studies. CMB B-mode polarization is the most effective probe to primordial gravitational waves (PGWs) and a test of the inflation as well as other theories of the early universe such as bouncing and cyclic universe. So far, all ground-based CMB polarization experiments are located in the southern hemisphere. Recently, China has launched the Ali CMB Polarization Telescopes (AliCPTs) in Tibet Plateau as a first ground-based CMB polarization experiment in the northern hemisphere to detect the PGWs. AliCPTs include two stages, the first one is to a telescope at the 5250m site (AliCPT-1) and the second one is to build a more sensitive telescope at a higher altitude of about 6000m (AliCPT-2). In this paper, we report the atmospherical condition, sky coverage and the current infrastructure associated with AliCPTs. We analyzed the reanalysis data from MERRA-2 together with radiosonde data of the Ali weather station and found that the amount of water vapor has a heavy seasonal variation and October to March is the suitable observation time. We also found 95/150 GHz to be feasible for AliCPT-1, and higher frequencies to be possible for AliCPT-2. Then we performed an analysis on observable sky and the target field, and showed that Ali provides us a unique opportunity to observe CMB with less foreground contamination in the northern hemisphere and is complementary to the existed southern CMB experiments. Together with the developed infrastructure, we point out that Ali opens a new window for CMB observation and will be one of the major sites in the world along with Antarctic and Chile.
While 2% of active galactic nuclei (AGNs) exhibit narrow emission lines with line-of-sight velocities that are significantly offset from the velocity of the host galaxy's stars, the nature of these velocity offsets is unknown. We investigate this question with Chandra/ACIS and Hubble Space Telescope/Wide Field Camera 3 observations of seven velocity-offset AGNs at z<0.12, and all seven galaxies have a central AGN but a peak in emission that is spatially offset by < kpc from the host galaxy's stellar centroid. These spatial offsets are responsible for the observed velocity offsets and are due to shocks, either from AGN outflows (in four galaxies) or gas inflowing along a bar (in three galaxies). We compare our results to a velocity-offset AGN whose velocity offset originates from a spatially offset AGN in a galaxy merger. The optical line flux ratios of the offset AGN are consistent with pure photoionization, while the optical line flux ratios of our sample are consistent with contributions from photoionization and shocks. We conclude that these optical line flux ratios could be efficient for separating velocity-offset AGNs into subgroups of offset AGNs -- which are important for studies of AGN fueling in galaxy mergers -- and central AGNs with shocks -- where the outflows are biased towards the most energetic outflows that are the strongest drivers of feedback.
Current searches for the gravitational-wave signature of compact binary mergers rely on matched-filtering data from interferometric observatories with sets of modelled gravitational waveforms. These searches currently use model waveforms that do not include the higher-order mode content of the gravitational-wave signal. Higher-order modes are important for many compact binary mergers and their omission reduces the sensitivity to such sources. In this work we explore the sensitivity loss incurred from omitting higher-order modes. We present a new method for searching for compact binary mergers using waveforms that include higher-order mode effects, and evaluate the sensitivity increase that using our new method would allow. We find that, when evaluating sensitivity at a constant rate-of-false alarm, and when including the fact that signal-consistency tests can reject some signals that include higher-order mode content, we observe a sensitivity increase of up to a factor of 2 in volume for high mass ratio, high total-mass systems. Our new search method is also directly applicable in searches for generic compact binaries.
The Eddington-inspired-Born-Infeld (EiBI) model is reformulated within the mimetic approach. In the presence of a mimetic field, the model contains non-trivial vacuum solutions which could be free of spacetime singularity because of the Born-Infeld nature of the theory. We study a realistic primordial vacuum universe and prove the existence of regular solutions, such as primordial inflationary solutions of de Sitter type or bouncing solutions. Besides, the linear instabilities present in the EiBI model are found to be avoidable for some interesting bouncing solutions in which the physical metric as well as the auxiliary metric are regular at the background level.
We describe a new class of dark energy (DE) models which behave like cosmological trackers at early times. These models are based on the $\alpha$-attractor set of potentials, originally discussed in the context of inflation. The new models allow the current acceleration of the universe to be reached from a wide class of initial conditions. Prominent examples of this class of models are the potentials $V_0\coth^p\vphi$ and $V_0\cosh{\lambda\vphi}$. %$V_0\cosh{\left(\lambda\vphi\right)}$. (i) At early times $\coth^p\vphi \propto \vphi^{-p}$, implying that $V(\vphi)$ has the same tracker properties as the inverse power law family of potentials. At late times $V \to V_0$ ensures that $w_0 \leq -0.8$ by $z\simeq 0$. (ii) The early time behaviour of $\cosh{\lambda\vphi} \propto e^{\lambda\vphi}$, ensures that DE tracks the background density in the universe. At late times $V_0\cosh{\lambda\vphi} \simeq V_0 \left (1 + \frac{1}{2}\lambda^2\vphi^2\right )$, implies that the DE equation of state approaches the attractor $w = -1$ via small oscillations. A remarkable feature of this new class of models is that they lead to $w_0 \leq -0.8$ from a very large initial basin of attraction. They therefore avoid the fine tuning problem which afflicts many models of DE.
We find a theoretical lower bound on the tensor-to-scalar ratio $r$ from a premise that extrapolation of the Higgs-field direction plays the role of the inflaton at high scales. We assume that all the non-minimal couplings are not particularly large, $\xi\lesssim 10^2$, so that the renormalizable low-energy effective field theory is reliable up to $10^{17}$ GeV ($\lesssim M_\text{P}/\sqrt{\xi}$). This framework includes the so-called critical Higgs inflation. In our analysis, we take into account the Higgs-portal scalar dark matter and the heavy right-handed neutrinos. The resultant bounds are rather stringent. In particular in the absence of the right-handed neutrinos, namely, when the right-handed-neutrino masses are smaller than $10^{13}$ GeV, the Planck bound $r<0.09$ implies that the dark-matter mass must be smaller than 1.2 TeV. On the other hand, the PandaX-II bound on the dark-matter mass $m_\text{DM}\gtrsim 750$ GeV leads to $r\gtrsim 4\times10^{-3}$. Both are within the range of near-future detection. When we include the right-handed neutrinos of mass $M_\text{R}\sim 10^{14}$ GeV, the allowed region becomes wider, but we still predict $r\gtrsim 10^{-3}$ in the most of the parameter space. The most conservative bound becomes $r>10^{-5}$ if we allow three-parameter tuning of $m_\text{DM}$, $M_\text{R}$, and the top-quark mass.
We describe methods designed to determine the astrophysical parameters of quasars based on spectra coming from the red and blue spectrophotometers of the Gaia satellite. These methods principally rely on two already published algorithms that are the weighted principal component analysis and the weighted phase correlation. The presented approach benefits from a fast implementation; an intuitive interpretation as well as strong diagnostic tools on the potential errors that may arise during predictions. The production of a semi-empirical library of spectra as they will be observed by Gaia is also covered and subsequently used for validation purpose. We detail the pre-processing that is necessary in order for these spectra to be fully exploitable by our algorithms along with the procedures that are used in order to predict the redshifts of the quasars; their continuum slopes; the total equivalent width of their emission lines and whether these are broad absorption line (BAL) quasars or not. Performances of these procedures were assessed in comparison with the Extremely Randomized Trees learning method and were proven to provide better results on the redshift predictions and on the ratio of correctly classified observations though the probability of detection of BAL quasars remains restricted by the low resolution of these spectra as well as by their limited signal-to-noise ratio. Finally, the triggering of some warning flags allows us to obtain an extremely pure subset of redshift predictions where approximately 99% of the observations come along with absolute errors that are below 0.1.
We study the cosmological effects of adding terms of higher-order in the usual energy-momentum tensor to the matter lagrangian of general relativity. This is in contrast to most studies of higher-order gravity which focus on generalising the Einstein-Hilbert curvature contribution to the lagrangian. The resulting cosmological theories include many particular theories, like bulk viscous cosmologies, loop quantum gravity, K-essence, and brane-world cosmologies. We find a range of exact solutions for isotropic universes, discuss their behaviours with reference to the early and late-time evolution, accelerated expansion, and the occurrence or avoidance of singularities. We briefly discuss extensions to anisotropic cosmologies and delineate the situations where the higher-order matter terms will dominate over anisotropies on approach to cosmological singularities.
We did a model independent phenomenological study of baryogenesis via leptogenesis, neutrinoless double beta decay (NDBD) and charged lepton flavour violation (CLFV) in a generic left-right symmetric model (LRSM) where neutrino mass originates from the type I + type II seesaw mechanism. We studied the new physics contributions to NDBD coming from the left-right gauge boson mixing and the heavy neutrino contribution within the framework of LRSM. We have considered the mass of the RH gauge boson to be specifically 5 TeV, 10 TeV and 18 TeV and studied the effects of the new physics contributions on the effective mass and baryogenesis and compared with the current experimental limit. We tried to correlate the cosmological BAU from resonant leptogenesis with the low energy observables, notably, NDBD and LFV with a view to finding a common parameter space where they coexists.
The large majority of the accreting supermassive black holes in the Universe are obscured by large columns of gas and dust. The location and evolution of this obscuring material have been the subject of intense research in the past decades, and are still highly debated. A decrease in the covering factor of the circumnuclear material with increasing accretion rates has been found by studies carried out across the electromagnetic spectrum. The origin of this trend has been suggested to be driven either by the increase in the inner radius of the obscuring material with incident luminosity due to the sublimation of dust; by the gravitational potential of the black hole; by radiative feedback; or by the interplay between outflows and inflows. However, the lack of a large, unbiased and complete sample of accreting black holes, with reliable information on gas column density, luminosity and mass, has left the main physical mechanism regulating obscuration unclear. Using a systematic multi-wavelength survey of hard X-ray-selected black holes, here we show that radiation pressure on dusty gas is indeed the main physical mechanism regulating the distribution of the circumnuclear material. Our results imply that the bulk of the obscuring dust and gas in these objects is located within the sphere of influence of the black hole (i.e., a few to tens of parsecs), and that it can be swept away even at low radiative output rates. The main physical driver of the differences between obscured and unobscured accreting black holes is therefore their mass-normalized accretion rate.
Links to: arXiv, form interface, find, astro-ph, recent, 1709, contact, help (Access key information)
We explore aperture mass mapping of large scale structures using the E- and B-modes produced in the weak lensing analysis of a field of galaxy clusters in Lynx. Deep multi-color Suprime-cam and Hubble Space Telescope imaging data are jointly analyzed to produce estimates of the locations and shear of background galaxies, which are then used to infer the locations and masses of foreground overdensities (E-modes) through the optimal filtering of axisymmetric tangential shears. By approximating this foreground structure of E-modes as a superposition of NFW-like halos, we model the observed ellipticity of each source galaxy as a sum of shears induced by foreground mass structures. We also make maps of the B-modes by similarly filtering the axisymmetric cross shear and show that these B-modes in fact contain information about the cluster masses and locations after identifying several expected sources of B-modes including edge effects, source clustering, and multiple lensing. We verify this reconstruction method using N-body simulation data and demonstrate how the observed B-modes naturally occur when background galaxies are sheared through a cosmic web of lenses.
Constraints on inflationary $B$-modes using Cosmic Microwave Background polarization data commonly rely on either template cleaning or cross-spectra between maps at different frequencies to disentangle galactic foregrounds from the cosmological signal. Assumptions about how the foregrounds scale with frequency are therefore crucial to interpreting the data. Recent results from the Planck satellite collaboration claim significant evidence for a decorrelation in the polarization signal of the spatial pattern of galactic dust between 353 GHz and 217 GHz. Such a decorrelation would suppress power in the cross spectrum between high frequency maps, where the dust is strong, and lower frequency maps, where the sensitivity to cosmological $B$-modes is strongest. Alternatively, it would leave residuals in lower frequency maps cleaned with a template derived from the higher frequency maps. If not accounted for, both situations would result in an underestimate of the dust contribution and thus an upward bias on measurements of the tensor-to-scalar ratio, $r$. In this paper we revisit this measurement and find that the no-decorrelation hypothesis cannot be excluded with the Planck data. There are three main reasons for this: i) there is significant noise bias in cross spectra between Planck data splits that needs to be accounted for; ii) there is strong evidence for unknown instrumental systematics whose amplitude we estimate using alternative Planck data splits; iii) there are significant correlations between measurements in different sky patches that need to be taken into account when assessing the statistical significance. Between $\ell=55-90$ and over $72\%$ of the sky, the dust $BB$ correlation between 217 GHz and 353 GHz is $1.001^{+.004/.021}_{-.004/.000}$ ($68\%~stat./syst.$) and shows no significant trend with sky fraction.
Redshift space distortions privilege the location of the observer in cosmological redshift surveys, breaking the translational symmetry of the underlying theory. This violation of statistical homogeneity has consequences for the modeling of clustering observables, leading to what are frequently called `wide angle effects'. We study these effects analytically, computing their signature in the clustering of the multipoles in configuration and Fourier space. We take into account both physical wide angle contributions as well as the terms generated by the galaxy selection function. Similar considerations also affect the way power spectrum estimators are constructed. We quantify, in an analytical way the biases which enter and clarify the relation between what we measure and the underlying theoretical modeling. The presence of an angular window function is also discussed. Motivated by this analysis we present new estimators for the three dimensional Cartesian power spectrum and bispectrum multipoles written in terms of spherical Fourier-Bessel coefficients. We show how the latter have several interesting properties, allowing in particular a clear separation between angular and radial modes.
We present EasyCritics, an algorithm to detect strongly-lensing groups and clusters in wide-field surveys without relying on a direct recognition of arcs. EasyCritics assumes that light traces mass and predicts the most likely locations of critical curves from the observed fluxes of luminous red early-type galaxies in the line of sight. The positions, redshifts and fluxes of these galaxies constrain the idealized gravitational lensing potential as a function of source redshift up to five free parameters, which are calibrated on few known lenses. From the lensing potential, EasyCritics derives the critical curves for a given, representative source redshift. EasyCritics is highly parallelized, uses fast Fourier methods and, optionally, GPU acceleration in order to process large datasets efficiently. The search of a $\smash{1 \, \mathrm{deg}^2}$ field of view requires less than 1 minute on a modern quad-core CPU, when using a pixel resolution of $0.25"/\mathrm{px}$. In this first part of a paper series on EasyCritics, we describe the main underlying concepts and present a first demonstration on data from the Canada-France-Hawaii-Telescope Lensing survey. We show that EasyCritics is able to identify known group- and cluster-scale lenses, including a cluster with two giant arc candidates that were previously missed by automated arc detectors. An additional null test on a candidate-free $\smash{1 \, \mathrm{deg}^2}$ field yields zero group- or cluster scale detections.
The origin of super-massive black holes in the early universe remains poorly understood.Gravitational collapse of a massive primordial gas cloud is a promising initial process,but theoretical studies have difficulty growing the black hole fast enough.We report numerical simulations of early black hole formation starting from realistic cosmological conditions.Supersonic gas motions left over from the Big Bang prevent early gas cloud formation until rapid gas condensation is triggered in a proto-galactic halo. A protostar is formed in the dense, turbulent gas cloud, and it grows by sporadic mass accretion until it acquires 34,000 solar masses.The massive star ends its life with a catastrophic collapse to leave a black hole -- a promising seed for the formation of a monstrous black hole.
The statistical properties of cosmic structures are well known to be strong probes for cosmology. In particular, several studies tried to use the cosmic void counting number to obtain tight constrains on Dark Energy. In this paper we address this question by using the CoSphere model as introduced in de Fromont & Alimi (2017a). We derive their exact statistics in both primordial and non linearly evolved Universe for the standard $\Lambda$CDM model. We first compute the full joint Gaussian probability distribution for the various parameters describing these profiles in the Gaussian Random Field. We recover the results of Bardeen et al. (1986) only in the limit where the compensation radius becomes very large, i.e. when the central extremum decouples from its cosmic environment. We derive the probability distribution of the compensation size in this primordial field. We show that this distribution is redshift independent and can be used to model cosmic void size distribution. Interestingly, it can be used for central maximum such as DM haloes. We compute analytically the statistical distribution of the compensation density in both primordial and evolved Universe. We also derive the statistical distribution of the peak parameters already introduced by Bardeen et al. (1986) and discuss their correlation with the cosmic environment. We thus show that small central extrema with low density are associated with narrow compensation regions with a small $R_1$ and a deep compensation density $\delta_1$ while higher central extrema are located in larger but smoother over/under massive regions.
We study cosmological perturbations in mimetic gravity in the presence of classified higher derivative terms which can make the mimetic perturbations stable. We show that the quadratic higher derivative terms which are independent of curvature and the cubic higher derivative terms which come from curvature corrections are sufficient to remove instabilities in mimetic perturbations. The advantage of working with the classified higher derivative terms is that we can control both the background and the perturbation equations allowing us to construct the higher derivative extension of mimetic dark matter and the mimetic nonsingular bouncing scenarios. The latter can be thought as a new higher derivative effective action for the loop quantum cosmology scenario in which the equations of motion coincide with those suggested by loop quantum cosmology. We investigate a possible connection between the mimetic cosmology and the Randall-Sundrum cosmology.
We construct models of inflation with many randomly interacting fields and use these to study the generation of cosmological observables. We model the potentials as multi-dimensional Gaussian random fields (GRFs) and identify powerful algebraic simplifications that, for the first time, make it possible to access the manyfield limit of inflation in GRF potentials. Focussing on small-field, slow-roll, approximate saddle-point inflation in potentials with structure on sub-Planckian scales, we construct explicit examples involving up to 100 fields and generate statistical ensembles comprising of 164,000 models involving 5 to 50 fields. For the subset of these that support at least sixty e-folds of inflation, we use the 'transport method' and $\delta N$ formalism to determine the predictions for cosmological observables at the end of inflation, including the power spectrum and the local non-Gaussianities of the primordial perturbations. We find three key results: i) Planck compatibility is not rare, but future experiments may rule out this class of models; ii) In the manyfield limit, the predictions from these models agree well with, but are sharper than, previous results derived using potentials constructed through non-equilibrium Random Matrix Theory; iii) Despite substantial multifield effects, non-Gaussianities are typically very small: $f_{\rm nl}^{\rm loc} \ll 1$. We conclude that many of the 'generic predictions' of single-field inflation can be emergent features of complex inflation models.
The use of high-quality simulated sky catalogs is essential for the success of cosmological surveys. The catalogs have diverse applications, such as investigating signatures of fundamental physics in cosmological observables, understanding the effect of systematic uncertainties on measured signals and testing mitigation strategies for reducing these uncertainties, aiding analysis pipeline development and testing, and survey strategy optimization. The list of applications is growing with improvements in the quality of the catalogs and the details that they can provide. Given the importance of simulated catalogs, it is critical to provide rigorous validation protocols that enable both catalog providers and users to assess the quality of the catalogs in a straightforward and comprehensive way. For this purpose, we have developed the DESCQA framework for the Large Synoptic Survey Telescope Dark Energy Science Collaboration as well as the broader community. The goal of DESCQA is to enable the inspection, validation, and comparison of an inhomogeneous set of synthetic catalogs via the provision of a common interface within an automated framework. In this paper, we present the design concept and first implementation of DESCQA. In order to establish and demonstrate its full functionality we use a set of interim catalogs and validation tests. We highlight several important aspects, both technical and scientific, that require thoughtful consideration when designing a validation framework, including validation metrics and how these metrics impose requirements on the synthetic sky catalogs.
We discuss a novel scenario for early cosmology, when the inflationary quasi-de Sitter phase dynamically originates from the initial quantum state represented by the microcanonical density matrix. This genuine quantum effect occurs as a result of the dynamics of the topologically nontrivial sectors in a (conjectured) strongly coupled QCD-like gauge theory in expanding universe. The crucial element of our proposal is the presence in our framework a nontrivial $\mathbb{S}^1$ which plays the dual role in construction: it defines the periodic gravitational instanton (on the gravity side) and it also defines a nontrivial gauge holonomy (on the gauge side) generating the vacuum energy. The effect is global in nature and cannot be formulated in terms of a gradient expansion in an effective local field theory. We also discuss a graceful exit from topological inflation due to the helical instability. The number of e-folds in the topological inflation framework is determined by the gauge coupling constant at the moment of inflation, and estimated as $N_{\rm infl}\sim \alpha^{-2}(H_0)\sim 10^2$. We analyze the equation of state in this framework at the end of inflation in terms of the gauge dynamics and confront our estimates with observations by computing the spectral index $n_s$ and tensor fraction $r$. Finally, we comment on the relation of our framework with no-boundary and tunneling cosmological proposals and their recent criticism.
We show that the present dark matter abundance can be accounted for by an oscillating scalar field that acquires both mass and a non-zero expectation value from interactions with the Higgs field. The dark matter scalar field can be sufficiently heavy during inflation, due to a non-minimal coupling to gravity, so as to avoid the generation of large isocurvature modes in the CMB anisotropies spectrum. The field begins oscillating after reheating, behaving as radiation until the electroweak phase transition and afterwards as non-relativistic matter. The scalar field becomes unstable, although sufficiently long-lived to account for dark matter, due to mass mixing with the Higgs boson, decaying mainly into photon pairs for masses below the MeV scale. In particular, for a mass of $\sim 7$ keV, which is effectively the only free parameter, the model predicts a dark matter lifetime compatible with the recent galactic and extragalactic observations of a 3.5 keV X-ray line.
We discuss the extent to which it is necessary to include higher-derivative operators in the effective field theory of general scalar-tensor theories. We explore the circumstances under which it is correct to restrict to second-order operators only, and demonstrate this using several different techniques, such as reduction of order and explicit field redefinitions. These methods are applied, in particular, to the much-studied Horndeski theories. The goal is to clarify the application of effective field theory techniques in the context of popular cosmological models, and to explicitly demonstrate how and when higher-derivative operators can be cast into lower-derivative forms suitable for numerical solution techniques.
We consider a self-interacting dark matter model in which the massive dark photon mediating the self-interaction decays to light dark fermions to avoid over-closing the universe. We find that if the model is constrained to explain the stellar kinematic data for spiral galaxies and galaxy clusters, it implies the presence of dark radiation, late kinetic decoupling for dark matter, and a suppressed linear power spectrum due to dark acoustic damping. The matter power spectrum is essentially fixed by the kinetic decoupling temperature and independent of other combinations of the parameters. We find the minimum halo mass is in the range of $10^5-10^8M_{\odot}$, with the upper limit coming from the Lyman-$\alpha$ forest power spectrum measurements. The presence of dark radiation and the damping of the matter power spectrum, in tandem with the impact of self-interactions in galactic halos, makes it possible to measure the gauge coupling and masses of the dark sector particles even when signals in conventional dark matter searches are absent.
Recently, the nonlinear electrodynamics (NED) has been gaining attention to generate primordial magnetic fields in the Universe and also to resolve singularity problems. Moreover, recent works have shown the crucial role of the NED on the inflation. This paper provides a new approach based on a new model of NED as a source of gravitation to remove the cosmic singularity at the big bang and explain the cosmic acceleration during the inflation era without initial singularity on the background of stochastic magnetic field. We explore whether a NED field can be the origin of the cosmic acceleration. Also, we found a realization of a cyclic Universe, free of initial singularity, due the model for the NED energy density we propose. We find explicit relations for $H(z)$ by direct integration of the equations of motion of the proposed model. We perform MCMC likelihood exploration of these relations using Observational Hubble data to find the mean values for the NED parameters. We compute the deceleration parameter $q(z)$ in the range $0<z<2$ from the best fit values of the parameters and find $q(z)\rightarrow 1/2$ at $z\rightarrow \infty$. Moreover, the Universe passes of a decelerated phase to an accelerated stage at redshift $\sim 0.5$. The result is that the are not statistical differences with the usual model during the radiation epoch which holds for $\alpha=0$. However, taking $\alpha$ slightly different from zero, we find that the NED with dust matter ($w_{m}=0$) is able to drive the late-time cosmic acceleration of the standard cosmological model.
In view of growing interest in tensor modes and their possible detection, we clarify the definition of tensor modes up to 2nd order in perturbation theory within the Hamiltonian formalism. Like in gauge theory, in cosmology the Hamiltonian is a suitable and consistent approach to reduce the gauge degrees of freedom. In this paper we employ the Faddeev-Jackiw method of Hamiltonian reduction. An appropriate set of gauge invariant variables that describe the dynamical degrees of freedom may be obtained by suitable canonical transformations in the phase space. We derive a set of gauge invariant variables up to 2nd order in perturbation expansion and for the first time we reduce the 3rd order action without adding gauge fixing terms. In particular, we are able to show the relation between the uniform-$\phi$ and Newtonian slicings, and study the difference in the definition of tensor modes in these two slicings.
In the following work, we compute the positron production from branon dark matter annihilations in order to constrain extra-dimensional theories. By having assumed that the positron fraction measured by AMS-02 is well explained just with astrophysical sources, exclusion diagrams for the branon mass and the tension of the brane, the two parameters characterising the branon phenomenology become possible. Our analysis has been performed for a minimal and a medium diffusion model in one extra dimension for both pseudo-isothermal and Navarro Frenck White dark matter haloes. Our constraints in the dark matter mass candidate range between 200 GeV and 100 TeV. Combined with previous cosmological analyses and experimental data in colliders, it allows us to set bounds on the parameter space of branons. In particular, we have discarded regions in the mass-tension diagram up to a branon mass of 28 TeV for the pseudo-Isothermal prole and minimal diffusion, and 63 TeV for the Navarro-Frenck-White profile and medium diffusion.
Our main interest is the evolution of domain walls of the Higgs field in the
early Universe. The aim of this paper is to understand how dynamics of Higgs
domain walls could be influenced by yet unknown interactions from beyond the
Standard Model. We assume that the Standard Model is valid up to certain, high,
energy scale $\Lambda$ and use the framework of the effective field theory to
describe physics below that scale. Performing numerical simulations with
different values of the scale $\Lambda$ we are able to extend our previous
analysis and determine its range of validity.
We study domain walls interpolating between the physical electroweak vacuum
and the vacuum appearing at very high field strengths. These domain walls could
be formed from non-homogeneous configurations of the Higgs field produced by
quantum fluctuations during inflation or thermal fluctuations during reheating.
Our numerical simulations show that evolution of Higgs domain walls is rather
insensitive to interactions beyond the Standard Model as long as masses of new
particles are grater than $10^{12}\ \textrm{GeV}$. For lower values of
$\Lambda$ the RG improved effective potential is strongly modified at field
strengths crucial to the evolution of domain walls. For instance its minima
become degenerate for $\Lambda$ around $10^{11}\ \textrm{GeV}$. We find that
even in the case when the minima of the potential are nearly degenerate Higgs
domain walls decayed shortly after their formation for generic initial
conditions. On the other hand, in simulations with specifically chosen initial
conditions Higgs domain walls can live longer and enter the scaling regime.
We also determine the energy spectrum of gravitational waves produced by
decaying domain walls of the Higgs field. For generic initial field
configurations the amplitude of the signal is too small to be observed in
present and planned detectors.
Links to: arXiv, form interface, find, astro-ph, recent, 1709, contact, help (Access key information)