In this paper, we present a new method to select the faint, background
galaxies used to derive the mass of galaxy clusters by weak lensing.
The method is based on the simultaneous analysis of the shear signal, that
should be consistent with zero for the foreground, unlensed galaxies, and of
the colors of the galaxies: photometric data from the COSMic evOlution Survey
are used to train the color selection. In order to validate this methodology,
we test it against a set of state-of-the-art image simulations of mock galaxy
clusters in different redshift [$0.23-0.45$] and mass
[$0.5-1.55\times10^{15}M_\odot$] ranges, mimicking medium-deep multicolor
imaging observations (e.g. SUBARU, LBT).
The performance of our method in terms of contamination by unlensed sources
is comparable to a selection based on photometric redshifts, which however
requires a good spectral coverage and is thus much more observationally
demanding. The application of our method to simulations gives an average ratio
between estimated and true masses of $\sim 0.98 \pm 0.09$. As a further test,
we finally apply our method to real data, and compare our results with other
weak lensing mass estimates in the literature: for this purpose we choose the
cluster Abell 2219 ($z=0.228$), for which multi-band (BVRi) data are publicly
available.
We present measurements of the spatial clustering statistics in redshift space of various scalar field modified gravity simulations. We utilise the two-point and the three-point correlation functions to quantify the spatial distribution of dark matter halos within these simulations and thus discern between the models. We compare $\Lambda$CDM simulations to various modified gravity scenarios and find consistency with previous work in terms of 2-point statistics in real and redshift-space. However using higher order statistics such as the three-point correlation function in redshift space we find significant deviations from $\Lambda$CDM hinting that higher order statistics may prove to be a useful tool in the hunt for deviations from General Relativity.
We present galaxy-galaxy lensing results from 139 square degrees of Dark Energy Survey (DES) Science Verification (SV) data. Our lens sample consists of red galaxies, known as redMaGiC, which are specifically selected to have a low photometric redshift error and outlier rate. The lensing measurement has a total signal-to-noise of 29, including all lenses over a wide redshift range $0.2 < z < 0.8$. Dividing the lenses into three redshift bins, we find no evidence for evolution in the halo mass with redshift. We obtain consistent results for the lensing measurement with two independent shear pipelines, ngmix and im3shape. We perform a number of null tests on the shear and photometric redshift catalogs and quantify resulting systematic errors. Covariances from jackknife subsamples of the data are validated with a suite of 50 mock surveys. The results and systematics checks in this work provide a critical input for future cosmological and galaxy evolution studies with the DES data and redMaGiC galaxy samples. We fit a Halo Occupation Distribution (HOD) model, and demonstrate that our data constrains the mean halo mass of the lens galaxies, despite strong degeneracies between individual HOD parameters.
We use two new hydrodynamical simulations of $\Lambda$CDM and $f(R)$ gravity to test the methodology used by Wilcox et al. 2015 (W15) in constraining the effects of a fifth force on the profiles of clusters of galaxies. We construct realistic simulated stacked weak lensing and X-ray surface brightness cluster profiles from these cosmological simulations, and then use these data projected along various lines-of-sight to test the spherical symmetry of our stacking procedure. We also test the applicability of the NFW profile to model weak lensing profiles of clusters in $f(R)$ gravity. Finally, we test the validity of the analytical model developed in W15 against the simulated profiles. Overall, we find our methodology is robust and broadly agrees with these simulated data. We also apply our full Markov Chain Monte Carlo (MCMC) analysis from W15 to our simulated X-ray and lensing profiles, providing consistent constraints on the modified gravity parameters as obtained from the real cluster data, e.g. for our $\Lambda$CDM simulation we obtain $|f_{\rm{R}0}| < 8.3 \times 10^{-5}$ (95% CL), which is in good agreement with the W15 measurement of $|f_{\rm{R}0}| < 6 \times 10^{-5}$. Overall, these tests confirm the power of our methodology which can now be applied to larger cluster samples available with the next generation surveys.
The investigation of any violation in the Cosmic Distance Duality Relation (CDDR) is one of the most important sources of investigation for a new physic. In this paper we propose a new method to find the origin of a possible violation on the CDDR. Such violation is defined from the equation $\frac{d_L}{d_A(1+z)^2} = \eta$, with $\eta \neq 1$. We analyze the observational constraints from SNIa, BAO and $f_{gas}$ for the parameter $\eta$ using three different parameterizations. We create three data sets with the following combinations: (Set I) $d_L$ data from SNIa and $d_A$ data from BAO measurements, (Set II) $d_L$ data from $f_{gas}$ and $d_A$ from BAO measurements and (Set III) $d_L$ from SNIa and $d_A$ from $f_{gas}$ measurements. The sets have 18 points and a redshift difference between the observational pairs of $\Delta z \leq 0.08$. It is found that the difference between Sets I and II is up to five times higher than Sets I and III, what suggest that a violation in the CDDR come from a new physics related with the angular diameter distance.
Gravitational waves (GWs) provide a revolutionary tool to investigate yet unobserved astrophysical objects. Especially the first stars, which are believed to be more massive than present-day stars, might be indirectly observable via the merger of their compact remnants. We develop a self-consistent, cosmologically representative, semi-analytical model to simulate the formation of the first stars and track the binary stellar evolution of the individual systems until the coalescence of the compact remnants. We estimate the contribution of primordial stars to the intrinsic merger rate density and to the detection rate of the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). Owing to their higher masses, the remnants of primordial stars produce strong GW signals, even if their contribution in number is relatively small. We find a probability of $\sim 1\%$ that the current detection GW150914 is of primordial origin. We estimate that aLIGO will detect roughly 1 primordial BH-BH merger per year for the final design sensitivity, although this rate depends sensitively on the primordial initial mass function. Turning this around, the detection of black hole mergers with a total binary mass of $\sim 300\,\mathrm{M}_\odot$ would enable us to constrain the primordial initial mass function.
We discovered two transient events in the Kepler field with light curves that
strongly suggest they are type II-P supernovae. Using the fast cadence of the
Kepler observations we precisely estimate the rise time to maximum for KSN2011a
and KSN2011d as 10.5$\pm 0.4$ and 13.3$\pm 0.4$ rest-frame days respectively.
Based on fits to idealized analytic models, we find the progenitor radius of
KSN2011a (280$\pm 20$ R$_\odot$) to be significantly smaller than that for
KSN2011d (490$\pm 20$ R$_\odot$) but both have similar explosion energies of
2.0$\pm 0.3\times 10^{51}$ erg.
The rising light curve of KSN2011d is an excellent match to that predicted by
simple models of exploding red supergiants (RSG). However, the early rise of
KSN2011a is faster than the models predict possibly due to the supernova
shockwave moving into pre-existing wind or mass-loss from the RSG. A mass loss
rate of $10^{-4}$ M$_\odot$ yr$^{-1}$ from the RSG can explain the fast rise
without impacting the optical flux at maximum light or the shape of the
post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the
circumstellar interaction suspected in the fast rising light curve. The early
light curve of KSN2011d does show excess emission consistent with model
predictions of a shock breakout. This is the first optical detection of a shock
breakout from a type II-P supernova.
We calculate particle production during inflation and in the early stages of reheating after inflation in models with a charged scalar field coupled to Abelian and non-Abelian gauge fields. A detailed analysis of the power spectra of primordial electric fields, magnetic fields and charge fluctuations at the end of inflation and preheating is provided. We carefully account for the Gauss constraints during inflation and preheating, and clarify the role of the longitudinal components of the electric field. We calculate the timescale for the back-reaction of the produced gauge fields on the inflaton condensate, marking the onset of non-linear evolution of the fields. We provide a prescription for initial conditions for lattice simulations necessary to capture the subsequent nonlinear dynamics. On the observational side, we find that the primordial magnetic fields generated are too small to explain the origin of magnetic fields on galactic scales and the charge fluctuations are well within observational bounds for the models considered in this paper.
We study the kinetic decoupling of light (lesssim 10 GeV) magnetic dipole dark matter (DM). We find that present bounds from collider, direct DM searches, and structure formation allow magnetic dipole DM to remain in thermal equilibrium with the early universe plasma until as late as the electron-positron annihilation epoch. This late kinetic decoupling leads to a minimal mass for the earliest dark protohalos of thousands of solar masses, in contrast to the conventional weak scale DM scenario where they are of order 10^{-6} solar masses.
We consider a massive vector field with derivative interactions that propagates only the 3 desired polarizations (besides two tensor polarizations from gravity) with second-order equations of motion in curved space-time. The cosmological implications of such generalized Proca theories are investigated for both the background and the linear perturbation by taking into account the Lagrangian up to quintic order. In the presence of a matter fluid with a temporal component of the vector field, we derive the background equations of motion and show the existence of de Sitter solutions relevant to the late-time cosmic acceleration. We also obtain conditions for the absence of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations in the small-scale limit. Our results are applied to concrete examples of the general functions in the theory, which encompass vector Galileons as a specific case. In such examples, we show that the de Sitter fixed point is always a stable attractor and study viable parameter spaces in which the no-ghost and stability conditions are satisfied during the cosmic expansion history.
We review the status of bouncing cosmologies as alternatives to cosmological inflation for providing a description of the very early universe, and a source for the cosmological perturbations which are observed today. We focus on the motivation for considering bouncing cosmologies, the origin of fluctuations in these models, and the challenges which various implementations face.
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The HST Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z=0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. The inclination of the mergers with respect to the plane of the sky poses significant observational challenges at X-ray wavelengths. MACS J1149.6+2223 possibly hosts a steep-spectrum radio halo. If the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular ICM morphology, could indicate that MACS J1149.6+2223 is an old merging cluster.
Scattering of cosmic microwave background (CMB) radiation in galaxy clusters induces polarization signals determined by the quadrupole anisotropy in the photon distribution at the location of clusters. This "remote quadrupole" derived from the measurements of the induced polarization in galaxy clusters provides an opportunity of reconstruction of local CMB temperature anisotropies. In this {\em Letter} we develop an algorithm of the reconstruction through the estimation of the underlying primordial gravitational potential, which is the origin of the CMB temperature and polarization fluctuations and CMB induced polarization in galaxy clusters. We found a nice reconstruction for the quadrupole and octopole components of the CMB temperature anisotropies with the assistance of the CMB induced polarization signals. The reconstruction can be an important consistency test on the puzzles of CMB anomaly, especially for the low quadrupole and axis of evil problems reported in WMAP and Planck data.
We modify upon the algorithm we proposed before in \citep{aghamousa_timedelay_1} on time delay estimation of the strong lens systems incorporating weighted cross correlation, defining two tuning parameters in the analysis and optimizing the method (deriving its parameters) by trading off between the bias and variance using many Monte Carlo simulations. We apply our proposed method on the light curves of the lensed quasar SDSS J1001+5027 since this system has been well studied by other groups to compare our results with their findings. In this work we propose two estimators namely "mean" and "mirror" estimators and we show that these two estimators should result to consistent and accurate estimations. Our mirror estimator results to $-117.1^{+1.6}_{-1.0}$ days time delay for this system and our mean estimator results to $-119.8^{+1.8}_{-0.8}$ days using Monte Carlo simulations to estimate the uncertainties. These two estimations are very much consistent with results of the other groups, however, the small discrepancy between these estimations hints towards some possible minor systematics in the data or inaccurate estimation of the uncertainties of the data epochs. Using simulations provided by \citep{COSMOGRAIL_XIV}, where they account for some possible systematics in the simulations, we got larger error bars on the estimated time delays while the mean estimated values remained unchanged.
The Beyond Horndeski class of alternative gravity theories allow for Self-accelerating de-Sitter cosmologies with no need for a cosmological constant. This makes them viable alternatives to $\Lambda$CDM and so testing their small-scale predictions against General Relativity is of paramount importance. These theories generically predict deviations in both the Newtonian force law and the gravitational lensing of light inside extended objects. Therefore, by simultaneously fitting the X-ray and lensing profiles of galaxy clusters new constraints can be obtained. In this work, we apply this methodology to the stacked profiles of 58 high-redshift ($ 0.1<z<1.2$) clusters using X-ray surface brightness profiles from the XMM Cluster Survey and weak lensing profiles from CFHTLenS. By performing a multi-parameter Markov chain Monte Carlo analysis, we are able to place new constraints on the parameters governing deviations from Newton's law $\Upsilon_{1}=-0.11^{+0.93}_{-0.67}$ and light bending $\Upsilon_{2}=-0.22^{+1.22}_{-1.19}$. Both constraints are consistent with General Relativity, for which $\Upsilon_{1}=\Upsilon_{2}=0$. We present here the first observational constraints on $\Upsilon_{2}$, as well as the first extragalactic measurement of both parameters.
We propose a test of single-scalar inflation based on using the well-measured scalar power spectrum to reconstruct the tensor power spectrum, up to a single integration constant. This sort of test can be used effectively, even when the tensor power spectrum is measured too poorly to resolve the tensor spectral index.
We present the first calculation of the cross-correlation between three-dimensional cosmic shear and the integrated Sachs-Wolfe (iSW) effect. Both signals are combined in a single formalism, which permits the computation of the full covariance matrix. In order to avoid the uncertainties presented by the non-linear evolution of the matter power spectrum and intrinsic alignments of galaxies, our analysis is restricted to large scales, i.e. multipoles below l=1000. We demonstrate in a Fisher analysis that this reduction compared to other studies of three-dimensional weak lensing extending to smaller scales is compensated by the information that is gained if the additional iSW signal and in particular its cross-correlation with lensing data are considered. Given the observational standards of upcoming weak lensing surveys like Euclid, marginal errors on cosmological parameters decrease by ten per cent compared to a cosmic shear experiment if both types of information are combined without a CMB prior. Once the constraining power of CMB data is added, the improvement becomes marginal.
In this letter we demonstrate the importance of including the lensing contribution in galaxy clustering analyses with large galaxy redshift surveys. It is well known that radial cross-correlations between different redshift bins of galaxy surveys are dominated by lensing. But we show here that also neglecting lensing in the auto-correlations within one bin severely biases cosmological parameter estimation with redshift surveys. It leads to significant shifts for several cosmological parameters, most notably the scalar amplitude, the scalar spectral index and in particular the neutrino mass scale. Especially the latter parameter is one of the main targets of future galaxy surveys.
We examine the projected ability to reconstruct the mass, scattering, and annihilation cross section of dark matter in the new generation of large underground detectors, XENON-1T, SuperCDMS, and DarkSide-G2, in combination with diffuse gamma radiation from expected 15 years of data from Fermi-LAT observation of 46 local spiral dwarf galaxies and projected CTA sensitivity to a signal from the Galactic Center. To this end we consider several benchmark points spanning a wide range of WIMP mass, different annihilation final states, and large enough event rates to warrant detection in one or more experiments. As previously shown, below some 100 GeV only direct detection experiments will in principle be able to reconstruct the WIMP mass well. This may, in case a signal at Fermi-LAT is also detected, additionally help restricting \sigma v and the allowed decay branching rates. In the intermediate range between some 100 GeV and up a few hundred GeV, direct and indirect detection experiments can be used in complementarity to ameliorate the respective determinations, which in individual experiments can at best be rather poor, thus making the WIMP reconstruction in this mass range very challenging. At large WIMP mass, ~1 TeV, CTA will have the ability to reconstruct mass, annihilation cross section, and the allowed decay branching rates to very good precision for the $\tau^+\tau^-$ or purely leptonic final state, good for the $W^+W^-$ case, and rather poor for $b\bar{b}$. An additional substantial improvement can potentially be achieved by reducing the systematic uncertainties, increasing exposure, or by an additional measurement at Fermi-LAT that would help reconstruct the annihilation cross section and the allowed branching fractions to different final states.
(abridged) We present cosmological constraints obtained from galaxy clusters identified by their Sunyaev-Zel'dovich effect signature in the 2500 square degree South Pole Telescope Sunyaev Zel'dovich survey. We consider the 377 cluster candidates identified at z>0.25 with a detection significance greater than five, corresponding to the 95% purity threshold for the survey. We compute constraints on cosmological models using the measured cluster abundance as a function of mass and redshift. We include additional constraints from multi-wavelength observations, including Chandra X-ray data for 82 clusters and a weak lensing-based prior on the normalization of the mass-observable scaling relations. Assuming a LCDM cosmology, where the species-summed neutrino mass has the minimum allowed value (mnu = 0.06 eV) from neutrino oscillation experiments, we combine the cluster data with a prior on H0 and find sigma_8 = 0.797+-0.031 and Omega_m = 0.289+-0.042, with the parameter combination sigma_8(Omega_m/0.27)^0.3 = 0.784+-0.039. These results are in good agreement with constraints from the CMB from SPT, WMAP, and Planck, as well as with constraints from other cluster datasets. Adding mnu as a free parameter, we find mnu = 0.14+-0.08 eV when combining the SPT cluster data with Planck CMB data and BAO data, consistent with the minimum allowed value. Finally, we consider a cosmology where mnu and N_eff are fixed to the LCDM values, but the dark energy equation of state parameter w is free. Using the SPT cluster data in combination with an H0 prior, we measure w = -1.28+-0.31, a constraint consistent with the LCDM cosmological model and derived from the combination of growth of structure and geometry. When combined with primarily geometrical constraints from Planck CMB, H0, BAO and SNe, adding the SPT cluster data improves the w constraint from the geometrical data alone by 14%, to w = -1.023+-0.042.
We use the most recent type Ia supernovae (SNe Ia) observations to perform a statistical comparison between the standard $\Lambda$CDM model and its extensions ($w$CDM and $w(z)$CDM) and some alternative cosmologies, namely: the Dvali--Gabadadze--Porrati (DGP) model, a power-law $f(R)$ scenario in the metric formalism and an example of vacuum decay ($\Lambda(t)$CDM) cosmology in which the dilution of pressureless matter is attenuated with respect to the usual $a^{-3}$ scaling due to the interaction of the dark matter and dark energy fields. We perform a Bayesian model selection analysis using the Affine-Invariant Ensemble Sampler Monte-Carlo method. In order to obtain the posterior distribution for the parameters of each model, we use the Joint Lightcurve Analysis (JLA) SNe Ia compilation containing 740 events in the interval $0.01 < z < 1.3$. The data are analysed with the SALT-II light-curve fitter and the model selection is then performed by computing the Bayesian evidence of each model and the Bayes factor between them. The results indicate that the JLA data only cannot distinguish the standard $\Lambda$CDM from its alternatives but their combination with current measurements of baryon acoustic oscillations can. We provide a rank order for the models considered and also discuss the influence of the $H_0$ priors on the results.
Warm dark matter cosmologies have been widely studied as an alternative to the cold dark matter paradigm, the characteristic feature being a suppression of structure formation on small cosmological scales. A very similar situation occurs if standard cold dark matter particles are kept in local thermal equilibrium with a, possibly dark, relativistic species until the universe has cooled down to keV temperatures. We perform a systematic phenomenological study of this possibility, and classify all minimal models containing dark matter and an arbitrary radiation component that allow such a late kinetic decoupling. We recover explicit cases recently discussed in the literature and identify new examples that are interesting from a model-building point of view. In some of these models dark matter is inevitably self-interacting, which is remarkable in view of recent observational support for this possibility. Hence, dark matter models featuring late kinetic decoupling have the potential not only to alleviate the missing satellites problem but also to address other problems of the cosmological concordance model on small scales, in particular the cusp-core and too-big-too-fail problems, in some cases without invoking any additional input.
A linear polarization field on the sphere can be uniquely decomposed into an E-mode and a B-mode component. These two components are analytically defined in terms of spin-2 spherical harmonics. Maps that contain filtered modes on a partial sky can also be decomposed into E-mode and B-mode components. However, the lack of full sky information prevents orthogonally separating these components using spherical harmonics. In this paper, we present a technique for decomposing an incomplete map into E and B-mode components using E and B eigenmodes of the pixel covariance in the observed map. This method is found to orthogonally define E and B in the presence of both partial sky coverage and spatial filtering. This method has been applied to the BICEP2 and the Keck Array maps and results in reducing E to B leakage from LCDM E-modes to a level corresponding to a tensor-to-scalar ratio of $r<1\times10^{-4}$.
In this letter, we show that the newly detected H.E.S.S. gamma-ray diffuse emission from the Galactic center below 0.45 deg can be accounted for by inverse Compton emission from millisecond pulsars and heavy (~ 100 TeV) dark matter annihilating to electrons or muons with a thermal or sub-thermal cross-section, provided that the dark matter density profile features a supermassive black hole-induced spike on sub-pc scales. We discuss the impact of the interstellar radiation field, magnetic field and diffusion set-up on the spectral and spatial morphology of the resulting emission. For well-motivated parameters, we show that the DM-induced emission reproduces the spatial morphology of the H.E.S.S. signal above ~ 10 TeV, while we obtain a more extended component from pulsars at lower energies, which could be used as a prediction for future H.E.S.S. observations.
We present a study of the optical properties of the 26 most massive galaxy clusters selected within the SPT-SZ 2500 deg$^2$ survey. This Sunyaev-Zel'dovich effect selected sample spans a redshift range of 0.10 < z < 1.13. We measure the galaxy radial profile, the luminosity function (LF), and the halo occupation number (HON) using optical data with a typical depth of $m^*$ + 2. The stacked radial profiles are consistent with a NFW profile with a concentration of $2.84^{+0.40}_{-0.37}$ for the red sequence (RS) and $2.36^{+0.38}_{-0.35}$ for the total population. Stacking the data in multiple redshift bins shows a hint of redshift evolution in the concentration when both the total population is used, and when only RS galaxies are used (at 2.1$\sigma$ and 2.8$\sigma$, respectively). The stacked LF shows a faint end slope $\alpha = -1.06^{+0.04}_{-0.03}$ for the total and $\alpha = -0.80^{+0.04}_{-0.03}$ for the RS population. The redshift evolution of $m^*$ is found to be consistent with a passively evolving Composite Stellar Population (CSP) model. By adopting the CSP model predictions, we explore the redshift evolution of the schechter parameters $\alpha$ and $\phi^*$. We find $\alpha$ for the total population to be consistent with no evolution (0.3$\sigma$), while evidence of evolution for the red galaxies is mildly significant (1.1-2.1$\sigma$). The data show that the density $\phi^*$/E$^2$(z) decreases with redshift, in tension with the self-similar expectation at a 2.4$\sigma$ level for the total population. The measured HON-mass relation has a lower normalization than previous studies at low redshift. Finally, our data support HON redshift evolution at a 2.1$\sigma$ level, with clusters at higher redshift containing fewer galaxies per unit mass to $m^*$ + 3 than their low-z counterparts [abridged].
We discuss models involving two scalar fields coupled to classical gravity that satisfy the general criteria: (i) the theory has no mass input parameters, (ii) classical scale symmetry is broken only through $-\frac{1}{12}\varsigma \phi^2 R$ couplings where $\varsigma$ departs from the special conformal value of $1$; (iii) the Planck mass is dynamically generated by the vacuum expectations values (VEVs) of the scalars (iv) there is a stage of viable inflation associated with slow roll in the two--scalar potential; (v) the final vacuum has a small to vanishing cosmological constant and an hierarchically small ratio of the VEVs and the ratio of the scalar masses to the Planck scale. This assumes the paradigm of classical scale symmetry as a custodial symmetry of large hierarchies.
We introduce a series of cosmological hydrodynamical simulations of Lstar (M_200 =10^11.7 - 10^12.3 Msol) and group-sized (M_200 = 10^12.7 - 10^13.3 Msol) haloes run with the model used for the EAGLE project, which additionally includes a non-equilibrium ionization and cooling module that follows 136 ions. The simulations reproduce the observed correlation, revealed by COS-Halos at z~0.2, between O VI column density at impact parameters b < 150 kpc and the specific star formation rate (sSFR=SFR/Mstar) of the central galaxy at z~0.2. We find that the column density of circumgalactic O VI is maximal in the haloes associated with Lstar galaxies, because their virial temperatures are close to the temperature at which the ionization fraction of O VI peaks (T~10^5.5 K). The higher virial temperature of group haloes (> 10^6 K) promotes oxygen to higher ionization states, suppressing the O VI column density. The observed NO VI-sSFR correlation therefore does not imply a causal link, but reflects the changing characteristic ionization state of oxygen as halo mass is increased. In spite of the mass-dependence of the oxygen ionization state, the most abundant circumgalactic oxygen ion in both Lstar and group haloes is O VII; O VI accounts for only 0.1% of the oxygen in group haloes and 0.9-1.3% with Lstar haloes. Nonetheless, the metals traced by O VI absorbers represent a fossil record of the feedback history of galaxies over a Hubble time; their characteristic epoch of ejection corresponds to z > 1 and much of the ejected metal mass resides beyond the virial radius of galaxies. For both Lstar and group galaxies, more of the oxygen produced and released by stars resides in the circumgalactic medium (within twice the virial radius) than in the stars and ISM of the galaxy.
The extensive ground-based spectroscopy campaign from the VIMOS Ultra-Deep Survey (VUDS), and the deep multi-wavelength photometry in three very well observed extragalactic fields (ECDFS, COSMOS, VVDS), allow us to investigate physical properties of a large sample (~4000 galaxies) of spectroscopically confirmed faint (i_{AB}<~25 mag) star-forming galaxies, with and without Lyman alpha in emission, at z~2-6. The fraction of Lyman alpha emitters (LAEs; equivalent width (EW)=>20A) increases from ~10% at z~2 to ~40% at z~5-6, which is consistent with previous studies that employ higher Lyman alpha EW cut. This increase in the LAE fraction could be, in part, due to a decrease in the dust content of galaxies as redshift increases. When we compare best-fit SED estimated stellar parameters for LAEs and non-LAEs, we find that E(B-V) is smaller for LAEs at all redshifts and the difference in the median E(B-V) between LAEs and non-LAEs increases as redshift increases, from 0.05 at z~2 to 0.1 at z~3.5 to 0.2 at z~5-6. For the luminosities probed here (~L*), we find that star formation rates (SFRs) and stellar masses of galaxies, with and without Lyman alpha in emission, show small differences such that, LAEs have lower SFRs and stellar masses compared to non-LAEs. This result could be a direct consequence of the sample selection. Our sample of LAEs are selected based on their continuum magnitudes and they probe higher continuum luminosities compared to narrow-band/emission line selected LAEs. Based on our results, it is important to note that all LAEs are not universally similar and their properties are strongly dependent on the sample selection, and/or continuum luminosities.
We present a detailed study of the static spherically symmetric solutions in de Rham-Gabadadze-Tolley (dRGT) theory. Since the diffeomorphism invariance can be restored by introducing the St\"{u}ckelberg fields $\phi^a$, there is new invariant $I^{ab}=g^{\mu\nu}\partial_{\mu}\phi^a\partial_\nu\phi^b$ in the massive gravity, which adds to the ones usually encountered in general relativity (GR). In the unitary gauge $\phi^a=x^\mu\delta_\mu^a$, any inverse metric $g^{\mu\nu}$ that has divergence including the coordinate singularity in GR would exhibit a singularity in the invariant $I^{ab}$. Therefore, there is no conventional Schwarzschild metric if we choose unitary gauge. In this paper, we obtain a self-consistent static spherically symmetric ansatz in the nonunitary gauge. Under this ansatz, we find that there are seven solutions including the Schwarzschild solution, Reissner-Nordstr\"{o}m solution and five other solutions. These solutions may possess an event horizon depending upon the physical parameters (Schwarzschild radius $r_s$, scalar charge $S$ and/or electric charge $Q$). If these solutions possess an event horizon, we show that the singularity of $I^{ab}$ is absent at the horizon. Therefore, these solutions may become candidates for black holes in dRGT.
In order to solve the fine-tuning problem of the cosmological constant, we propose a simple model with the vacuum energy non-minimally coupled to the inflaton field. In this model, the vacuum energy decays to the inflaton during pre-inflation and inflation eras, so that the cosmological constant effectively deflates from the Planck mass scale to a much smaller one after inflation and plays the role of dark energy in the late-time of the universe. We show that our deflationary scenario is applicable to arbitrary slow-roll inflation models. We also take two specific inflation potentials to illustrate our results.
The covariant and gauge invariant calculation of the current expectation value in the homogeneous electric field in 1+3 dimensional de Sitter spacetime is shown. The result accords with previous work obtained by using adiabatic subtraction scheme. We therefore conclude the counterintuitive behaviors of the current in the infrared (IR) regime such as IR hyperconductivity and negative current are not artifacts of the renormalization scheme, but are real IR effects of the spacetime.
We discuss the possibility that dark matter corresponds to an oscillating scalar field coupled to the Higgs boson. We argue that the initial field amplitude should generically be of the order of the Hubble parameter during inflation, as a result of its quasi-de Sitter fluctuations. This implies that such a field may account for the present dark matter abundance for masses in the range $10^{-6} - 10^{-4}$ eV, if the tensor-to-scalar ratio is within the range of planned CMB experiments. We show that such mass values can naturally be obtained through either Planck-suppressed non-renormalizable interactions with the Higgs boson or, alternatively, through renormalizable interactions within the Randall-Sundrum scenario, where the dark matter scalar resides in the bulk of the warped extra-dimension and the Higgs is confined to the infrared brane.
We developed a hierarchical Bayesian model (HBM) to investigate how the presence of Seyfert activity relates to their environment, herein represented by the galaxy cluster mass, $M_{200}$, and the normalized cluster centric distance, $r/r_{200}$. We achieved this by constructing an unbiased sample of galaxies from the Sloan Digital Sky Survey, with morphological classifications provided by the Galaxy Zoo Project. A propensity score matching approach is introduced to control for the effects of confounding variables: stellar mass, galaxy colour, and star formation rate. The connection between Seyfert-activity and environmental properties in the de-biased sample is modelled within a HBM framework using the so-called logistic regression technique, suitable for the analysis of binary data (e.g., whether or not a galaxy hosts an AGN). Unlike standard ordinary least square fitting methods, our methodology naturally allows modelling the probability of Seyfert-AGN activity in galaxies on their natural scale, i.e. as a binary variable. Furthermore, we demonstrate how a HBM can incorporate information of each particular galaxy morphological type in an unified framework. In elliptical galaxies our analysis indicates a strong correlation of Seyfert-AGN activity with $r/r_{200}$, and a weaker correlation with the mass of the host. In spiral galaxies these trends do not appear, suggesting that the link between Seyfert activity and the properties of spiral galaxies are independent of the environment.
The diffuse cosmic X-ray background (CXB) is the sum of the emission of discrete sources, mostly massive black-holes accreting matter in active galactic nuclei (AGN). The CXB spectrum differs from the integration of the spectra of individual sources, calling for a large population, undetected so far, of strongly obscured Compton thick AGN. Such objects are predicted by unified models, which attribute most of the AGN diversity to their inclination on the line of sight, and play an important role for the understanding of the growth of black holes in the early Universe. The fraction of obscured AGN at low redshift can be derived from the observed CXB spectrum assuming AGN spectral templates and luminosity functions. We show that high signal-to-noise average hard X-ray spectra, derived from more than a billion seconds of effective exposure time with the Swift/BAT instrument, imply that mildly obscured Compton thin AGN feature a strong reflection and contribute massively to the CXB. A population of Compton thick AGN larger than that effectively detected is not required, as no more than 6\% of the CXB flux can be attributed to them. The stronger reflection observed in mildly obscured AGN suggests that the covering fraction of the gas and dust surrounding their central engines is a key factor in shaping their appearance. These mildly obscured AGN are easier to study at high redshift than Compton thick sources.
We discuss the correlation function for the metric for homogeneous and isotropic cosmologies. The exact propagator equation determines the correlation function as the inverse of the second functional derivative of the quantum effective action, for which we take the Einstein-Hilbert approximation. This formulation relates the metric correlation function employed in quantum gravity computations to cosmological observables as the graviton power spectrum. While the graviton correlation function can be obtained equivalently as a solution of the linearized Einstein equations, this does not hold for the vector and scalar components of the metric. We project the metric fluctuations on the subspace of "physical fluctuations", which couple to a conserved energy momentum tensor. On the subspace of physical metric fluctuations the relation to physical sources becomes invertible, such that the effective action and its relation to correlation functions does not need gauge fixing. The physical metric fluctuations have a similar status as the Bardeen potentials, while being formulated in a covariant way. We compute the effective action for the physical metric fluctuations for geometries corresponding to realistic cosmologies.
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Mass measurements of astronomical objects are most wanted but still elusive. We need them to trace the formation and evolution of cosmic structure but we can get direct measurements only for a minority. This lack can be circumvented with a proxy and a scaling relation. The twofold goal of estimating the unbiased relation and finding the right proxy value to plug in can be hampered by systematics, selection effects, Eddington/Malmquist biases and time evolution. We present a Bayesian hierarchical method which deals with these issues. Masses to be predicted are treated as missing data in the regression and are estimated together with the scaling parameters. The calibration subsample with measured masses does not need to be representative of the full sample. We apply the method to forecast weak lensing calibrated masses of the Planck, redMaPPer and MCXC clusters. Planck masses are biased low with respect to weak lensing calibrated masses, with a bias more pronounced for high redshift clusters. MCXC masses are under-estimated by ~ 20 per cent, which may be ascribed to hydrostatic bias. Catalogs are made available with the paper.
The Integrated Sachs-Wolfe (ISW) effect is a large-angle modulation of the cosmic microwave background (CMB), generated when CMB photons traverse evolving potential wells associated with large scale structure (LSS). Recent efforts have been made to reconstruct maps of the ISW signal using information from surveys of galaxies and other LSS tracers, but investigation into how survey systematics affect their reliability has so far been limited. Using simulated ISW and LSS maps, we study the impact of galaxy survey properties and systematic errors on the accuracy of reconstructed ISW signal. We find that systematics that affect the observed distribution of galaxies along the line of sight, such as photo-z and bias-evolution related errors, have a relatively minor impact on reconstruction quality. In contrast, however, we find that direction-dependent calibration errors can be very harmful. Specifically, we find that in order to avoid significant degradation of our reconstruction quality statistics, direction-dependent number density fluctuations due to systematics must be controlled so that their variance is smaller than $10^{-6}$ (which corresponds to a 0.1% calibration). Additionally, we explore the implications of our results for attempts to use reconstructed ISW maps to shed light on the origin of large-angle CMB alignments. We find that there is only a weak correlation between the true and reconstructed angular momentum dispersion, which quantifies alignment, even for reconstructed ISW maps which are fairly accurate overall.
Atom interferometry experiments are searching for evidence of chameleon scalar fields with ever-increasing precision. As experiments become more precise, so too must theoretical predictions. Previous work has made numerous approximations to simplify the calculation, which in general requires solving a 3-dimensional nonlinear partial differential equation (PDE). In this paper, we introduce a new technique for calculating the chameleonic force, using a numerical relaxation scheme on a uniform grid. This technique is more general than previous work, which assumed spherical symmetry to reduce the PDE to a 1-dimensional ordinary differential equation (ODE). We examine the effects of approximations made in previous efforts on this subject, and calculate the chameleonic force in a set-up that closely mimics the recent experiment of Hamilton et al. Specifically, we simulate the vacuum chamber as a cylinder with dimensions matching those of the experiment, taking into account the backreaction of the source mass, its offset from the center, and the effects of the chamber walls. Remarkably, the acceleration on a test atomic particle is found to differ by only 20% from the approximate analytical treatment. These results allow us to place rigorous constraints on the parameter space of chameleon field theories, although ultimately the constraint we find is the same as the one we reported in Hamilton et al. because we had slightly underestimated the size of the vacuum chamber. This new computational technique will continue to be useful as experiments become even more precise, and will also be a valuable tool in optimizing future searches for chameleon fields and related theories.
The sources that drove cosmological reionization left clues regarding their identity in the slope and inhomogeneity of the ultraviolet ionizing background (UVB): Bright quasars (QSOs) generate a hard UVB with predominantly large-scale fluctuations while Population II stars generate a softer one with smaller-scale fluctuations. Metal absorbers probe the UVB's slope because different ions are sensitive to different energies. Likewise, they probe spatial fluctuations because they originate in regions where a galaxy-driven UVB is harder and more intense. We take a first step towards studying the reionization-epoch UVB's slope and inhomogeneity by comparing observations of 12 metal absorbers at $z\sim6$ versus predictions from a cosmological hydrodynamic simulation using three different UVBs: a soft, spatially-inhomogeneous "galaxies+QSOs" UVB; a homogeneous "galaxies+QSOs" UVB (Haardt & Madau 2012); and a QSOs-only model. All UVBs reproduce the observed column density distributions of CII, SiIV, and CIV reasonably well although high-column, high-ionization absorbers are underproduced, reflecting numerical limitations. With upper limits treated as detections, only a soft, fluctuating UVB reproduces both the observed SiIV/CIV and CII/CIV distributions. The QSOs-only UVB overpredicts both CIV/CII and CIV/SiIV, indicating that it is too hard. The Haardt & Madau (2012) UVB underpredicts CIV/SiIV, suggesting that it lacks amplifications near galaxies. Hence current observations prefer a soft, fluctuating UVB as expected from a predominantly Population II background although they cannot rule out a harder one. Future observations probing a factor of two deeper in metal column density will distinguish between the soft, fluctuating and QSOs-only UVBs.
We present a numerical evidence that the amplitude and slope of the bound-zone peculiar velocity profile grow at the constant rates in a LambdaCDM universe. Analyzing the friends-of-friends halo catalogs from the Millennium-II simulations at various redshifts, we measure the average peculiar velocity profile of the objects located in the bound zone around massive group-size halos and compare it to an analytic formula characterized by the amplitude and slope parameters. It is shown that the amplitude and slope of the bound-zone peculiar velocity profile remain constant in the dark matter dominated epoch but begin to grow linearly with redshift after the onset of the Lambda-domination. Our explanation for this phenomenon is that as the balance between the gravitational attraction of the massive groups and the repulsive force of the Hubble expansion cracks up in the Lambda-dominated epoch, the gravitational influence on the bound-zone halos diminishes more rapidly with the increment of the radial distances. Speculating that the constant growth rate of the amplitude and slope of the bound-zone peculiar velocity profile is a unique feature of a Lambda-dominated universe, we suggest that the redshift evolution of the amplitude and slope of the bound-zone peculiar velocity profile should be a powerful local discriminator of dark energy candidates.
This is the third in a series of papers that develop a new and flexible model to predict weak-lensing (WL) peak counts, which have been shown to be a very valuable non-Gaussian probe of cosmology. In this paper, we compare the cosmological information extracted from WL peak counts using different filtering techniques of the galaxy shear data, including linear filtering with a Gaussian and two compensated filters (the starlet wavelet and the aperture mass), and the nonlinear filtering method MRLens. We present improvements to our model that account for realistic survey conditions, which are masks, shear-to-convergence transformations, and non-constant noise. We create simulated peak counts from our stochastic model, from which we obtain constraints on the matter density $\Omega_\mathrm{m}$, the power spectrum normalization $\sigma_8$, and the dark-energy parameter $w_0^\mathrm{de}$. We use two methods for parameter inference, a copula likelihood, and approximate Bayesian computation (ABC). We measure the contour width in the $\Omega_\mathrm{m}$-$\sigma_8$ degeneracy direction and the figure of merit to compare constraints from different filtering techniques. We find that starlet filtering outperforms the Gaussian kernel, and that including peak counts from different scales helps to lift parameter degeneracies. Peak counts from different smoothing scales with a compensated filter show very little cross-correlation, and adding information from different scales can therefore strongly enhance the available information. Measuring peak counts separately from different scales yields tighter constraints than using a combined peak histogram from a single map that includes multiscale information. Our results suggest that a compensated filter function with counts included separately from different smoothing scales yields the tightest constraints on cosmological parameters from WL peaks.
Future dedicated radio interferometers, including HERA and SKA, are very promising tools that aim to study the epoch of reionization and beyond via measurements of the 21 cm signal from neutral hydrogen. Dark matter (DM) annihilations into charged particles change the thermal history of the Universe and, as a consequence, affect the 21 cm signal. Accurately predicting the effect of DM strongly relies on the modeling of annihilations inside halos. In this work, we use up-to-date computations of the energy deposition rates by the products from DM annihilations, a proper treatment of the contribution from DM annihilations in halos, as well as values of the annihilation cross section allowed by the most recent cosmological measurements from the Planck satellite. Given current uncertainties on the description of the astrophysical processes driving the epochs of reionization, X-ray heating and Lyman-$\alpha$ pumping, we find that disentangling DM signatures from purely astrophysical effects, related to early-time star formation processes or late-time galaxy X-ray emissions, will be a challenging task. We conclude that only annihilations of DM particles with masses of $\sim100$ MeV, could leave an unambiguous imprint on the 21 cm signal and, in particular, on the 21 cm power spectrum. This is in contrast to previous, more optimistic results in the literature, which have claimed that strong signatures might also be present even for much higher DM masses. Additional measurements of the 21 cm signal at different cosmic epochs will be crucial in order to break the strong parameter degeneracies between DM annihilations and astrophysical effects and undoubtedly single out a DM imprint for masses different from $\sim100$ MeV.
Measurements of the non-Gaussianity of the primordial density field have the power to considerably improve our understanding of the physics of inflation. Indeed, if we can increase the precision of current measurements by an order of magnitude, a null-detection would rule out many classes of scenarios for generating primordial fluctuations. Large-scale galaxy redshift surveys represent experiments that hold the promise to realise this goal. Thus, we model the galaxy bispectrum and forecast the accuracy with which it will probe the parameter $f_{\rm NL}$, which represents the degree of primordial local-type non Gaussianity. Specifically, we address the problem of modelling redshift space distortions (RSD) in the tree-level galaxy bispectrum including $f_{\rm NL}$. We find novel contributions associated with RSD, with the characteristic large scale amplification induced by local-type non-Gaussianity. These RSD effects must be properly accounted for in order to obtain un-biased measurements of $f_{\rm NL}$ from the galaxy bispectrum. We propose an analytic template for the monopole which can be used to fit against data on large scales, extending models used in the recent measurements. Finally, we perform idealised forecasts on $\sigma_{f_{\rm NL}}$ -- the accuracy of the determination of local non-linear parameter $f_{\rm NL}$ -- from measurements of the galaxy bispectrum. Our findings suggest that current surveys can in principle provide $f_{\rm NL}$ constraints competitive with Planck, and future surveys could improve them further.
As the 2015 results of Plancks mission have recently been made available, it is interesting to check the evolution of the scale factor and of the Hubble parameter in the light of these results. Two models in line with Einsteins field equations and with the hot big bang scenario for a flat Universe are used to allow a comparison : (1) the classical one using density parameters for matter content (baryonic and dark matter) and dark energy ; (2) an alternative model, already used in the past, and assuming the Hubble parameter to contain a term constant in time. Both models are coherent with each other except for some discrepancy about the density, which can be ascribed to the different hypotheses made. This opens a way for further interpretation of the origin of dark matter and dark energy.
We investigate the modified $F(R)$ gravity theory with the function $F(R) = (1-\sqrt{1-2\lambda R-\sigma (\lambda R)^2})/\lambda$. The action is converted into Einstein$-$Hilbert action at small values of $\lambda$ and $\sigma$. The local tests give a bound on the parameters, $\lambda(1+\sigma)\leq 2\times 10^{-6}$ cm$^2$. The Jordan and Einstein frames are considered, the potential, and the mass of the scalar field were obtained. The constant curvature solutions of the model are found. It was demonstrated that the de Sitter space is unstable but a solution with zero Ricci scalar is stable. The cosmological parameters of the model are evaluated. Critical points of autonomous equations are obtained and described.
Giant radio relics are the arc-shaped diffuse radio emission regions observed in the outskirts of some merging galaxy clusters. They are believed to trace shock-waves in the intra-cluster medium. Recent observations demonstrated that some prominent radio relics exhibit a steepening above 2 GHz in their radio spectrum. This challenges standard theoretical models because shock acceleration is expected to accelerate electrons to very high energies with a power-law distribution in momentum. In this work we attempt to reconcile these data with the shock-acceleration scenario. We propose that the spectral steepening may be caused by the highest energy electrons emitting preferentially in lower magnetic fields than the bulk of synchrotron bright electrons in relics. Here, we focus on a model with an increasing mag- netic field behind the shock front, which quickly saturates and then declines. We derive the time-evolution of cosmic-ray electron spectra in time variable magnetic fields and an expanding medium. We then apply the formalism on the large radio relic in the cluster CIZA J2242.8+5301 (the Sausage relic). We show that under favourable circumstances of magnetic field amplification downstream, our model can explain the observed radio spectrum, the brightness profile and the spectral index profile of the relic. A possible interpretation for the required amplification of the magnetic field downstream is a dynamo acting behind the shock with an injection scale of magnetic turbulence of about 10 kpc. Our models require injection efficiencies of CRe - which are in tension with simple diffusive shock acceleration from the thermal pool. We show that this problem can likely be alleviated considering pre-existing CRe.
Pulsar timing arrays are now setting increasingly tight limits on the gravitational wave background from binary supermassive black holes. But as upper limits grow more constraining, what can be implied about galaxy evolution? We investigate which astrophysical parameters have the largest impact on strain spectrum predictions and provide a simple framework to directly translate between measured values for the parameters of galaxy evolution and PTA limits on the gravitational wave background of binary supermassive black holes. We find that the most influential observable is the relation between a host galaxy's central bulge and its central black hole, $\mbox{$M_{\bullet}$-$M_{\rm bulge}$}$, which has the largest effect on the mean value of the characteristic strain amplitude. However, the variance of each prediction is dominated by uncertainties in the galaxy stellar mass function. Using this framework with the best published PTA limit, we can set limits on the shape and scatter of the $\mbox{$M_{\bullet}$-$M_{\rm bulge}$}$ relation. We find our limits to be in contention with strain predictions using two leading measurements of this relation. We investigate several possible reasons for this disagreement. If we take the $\mbox{$M_{\bullet}$-$M_{\rm bulge}$}$ relations to be correct within a simple power-law model for the gravitational wave background, then the inconsistency is reconcilable by allowing for an additional `stalling' time between a galaxy merger and evolution of a binary supermassive black hole to sub-parsec scales, with lower limits on this timescale of $\sim 1-2$ Gyr.
We apply a friends-of-friends algorithm to an enhanced SDSS DR12 spectroscopic catalog including redshift from literature to construct a catalog of $1588~N\ge3$ compact groups of galaxies containing 5179 member galaxies and covering the redshift range $0.01 < z < 0.19$. This catalog contains 18 times as many systems and reaches 3 times the depth of similar catalog of Barton et al. (1996). We construct catalogs from both magnitude-limited and volume-limited galaxy samples. Like Barton et al. (1996) we omit the frequently applied isolation criterion in the compact group selection algorithm. Thus the groups selected by fixed projected spatial and rest frame line-of-sight velocity separation produce a catalog of groups with a redshift independent median size. In contrast with previous catalogs, the enhanced SDSS DR12 catalog (including galaxies with $r < 14.5$) includes many systems with $z\leq 0.05$. The volume-limited samples are unique to this study. The compact group candidates in these samples have a median stellar mass independent of redshift. Groups with velocity dispersion $\leq 100$ km s$^{-1}$ show abundant evidence for ongoing dynamical interactions among the members. The number density of the volume-limited catalogs agrees with previous catalogs at the lowest redshifts but decreases as the redshift increases. The SDSS fiber placement constraints limit the catalog completeness. In spite of this issue the volume-limited catalogs provide a promising basis for detailed spatially resolved probes of the impact of galaxy-galaxy interactions within similar dense systems over a broad redshift range.
We propose a mechanism to generate a nearly scale-invariant spectrum of adiabatic scalar perturbations about a stable, ekpyrotic background. The key ingredient is a coupling between a single ekpyrotic field and a perfect fluid of ultra-relativistic matter. This coupling introduces a friction term into the equation of motion for the field, opposing the Hubble anti-friction, which can be chosen such that an exactly scale-invariant (or nearly scale-invariant) spectrum of adiabatic density perturbations is continuously produced throughout the ekpyrotic phase. This mechanism eliminates the need for a second (entropic) scalar field and hence any need for introducing a second phase for converting entropic into curvature fluctuations. It also reduces the constraints on the equation of state during the ekpyrotic phase and, thereby, the need for parametric fine-tuning.
In this paper we present an initial exploration of the Calabi-Yau landscape in the context of Kahler moduli inflation. We review how the slow-roll requirement on the scalar potential translates to a geometric constraint on the Kahler geometry of the vacuum. This constraint leads to a hard bound on the moduli space geometry and we consider the effects of this constraint on the string landscape that arises in type IIB string compactifications on an O3/O7 orientifold. Most notably we find that the inflationary constraint is independent of the moduli space dimension and only 6.57% of geometries inspected support high-scale Kahler moduli inflation.
We consider the possibility to produce a bouncing universe in the framework of scalar-tensor gravity when the scalar field has a nonconformal coupling to the Ricci scalar. We prove that bouncing universes regular in the future with essentially the same dynamics as for the conformal coupling case do exist when the coupling deviates slightly from it. This is found numerically for more substantial deviations as well. In some cases however new features are found like the ability of the system to leave the effective phantom regime.
Successful inflationary models should (i) describe the data well; (ii) arise generically from sensible UV completions; (iii) be insensitive to detailed fine-tunings of parameters and (iv) make interesting new predictions. We argue that a class of models with these properties is characterized by relatively simple potentials with a constant term and negative exponentials. We here continue earlier work exploring UV completions for these models, including the key (though often ignored) issue of modulus stabilisation, to assess the robustness of their predictions. We show that string models where the inflaton is a fibration modulus seem to be robust due to an effective rescaling symmetry, and fairly generic since most known Calabi-Yau manifolds are fibrations. This class of models is characterized by a generic relation between the tensor-to-scalar ratio $r$ and the spectral index $n_s$ of the form $r \propto (n_s -1)^2$ where the proportionality constant depends on the nature of the effects used to develop the inflationary potential and the topology of the internal space. In particular we find that the largest values of the tensor-to-scalar ratio that can be obtained by generalizing the original set-up are of order $r \lesssim 0.01$. We contrast this general picture with specific popular models, such as the Starobinsky scenario and $\alpha$-attractors. Finally, we argue the self consistency of large-field inflationary models can strongly constrain non-supersymmetric inflationary mechanisms.
We investigated the optical/ultraviolet (UV) color variations for a sample of 2169 quasars based on multi-epoch spectroscopy in the Sloan Digital Sky Survey (SDSS) data release seven (DR7) and data release nine (DR9). To correct the systematic difference between DR7 and DR9 due to the different instrumental setup, we produced a correction spectrum by using a sample of F-stars observed both in DR7 and DR9. The correction spectrum was then applied to quasars when comparing the spectra of DR7 with DR9. In each object, the color variation was explored by comparing the spectral index of the continuum power-law fit on the brightest spectrum with the faintest one, and also by the shape of their difference spectrum. In 1876 quasars with consistent color variations from two methods, we found that most sources (1755, $\sim 94\%$) show bluer-when-brighter (BWB) trend, and the redder-when-brighter (RWB) trend is only detected in 121 objects ($\sim 6\%$). The common BWB trend is supported by the bluer composite spectrum constructed from bright spectra than that from faint spectra, and also by the blue composite difference spectrum. The correction spectrum is proved to be highly reliable by comparing the composite spectrum from corrected DR9 and original DR7 spectra. Assuming that the optical/UV variability is triggered by fluctuations, RWB trend can likely be explained if the fluctuations occur firstly at outer disk region, and the inner disk region has not fully responded yet when the fluctuation being propagated inward. In contrast, the common BWB trend implies that the fluctuations are likely more often happening firstly in inner disk region.
The SHELS (Smithsonian Hectospec Lensing Survey) is a complete redshift survey covering two well-separated fields (F1 and F2) of the Deep Lens Survey. Both fields are more than 94% complete to a Galactic extinction corrected R0 = 20.2. Here we describe the redshift survey of the F1 field centered at R.A. = 00h53m25.3s and Decl = 12d33m55s; like F2, the F1 field covers 4 sq deg. The redshift survey of the F1 field includes 9426 new galaxy redshifts measured with Hectospec on the MMT (published here). As a guide to future uses of the combined survey we compare the mass metallicity relation and the distributions of D4000 as a function of stellar mass and redshift for the two fields. The mass-metallicity relations differ by an insignificant 1.6 sigma. For galaxies in the stellar mass range 1.e10 to 1.e11 MSun, the increase in the star-forming fraction with redshift is remarkably similar in the two fields. The seemingly surprising 31-38% difference in the overall galaxy counts in F1 and F2 is probably consistent with the expected cosmic variance given the subtleties of the relative systematics in the two surveys. We also review the Deep Lens Survey cluster detections in the two fields: poorer photometric data for F1 precluded secure detection of the single massive cluster at z = 0.35 that we find in SHELS. Taken together the two fields include 16,055 redshifts for galaxies with R0 <= 20.2 and 20,754 redshifts for galaxies with R <= 20.6. These dense surveys in two well-separated fields provide a basis for future investigations of galaxy properties and large-scale structure.
The recent discovery of the gravitational wave source GW150914 has revealed a coalescing binary black hole (BBH) with masses of $\sim 30~\odot$. A possible origin of such a massive binary is Population III (PopIII) stars. PopIII stars are efficient producers of BBHs and of a gravitational wave background (GWB) in the $10-100$ Hz band, and also of ionizing radiation in the early Universe. We show that PopIII stars that are consistent with the recent Planck measurement of a low electron scattering optical depth $\tau_{\rm e}=0.066\pm0.016$ could still produce a GWB dominating other binary populations. Moreover, the spectral index of the background from PopIII BBHs becomes flatter at $f\gtrsim 20$ Hz than the value ${\rm d}\ln \Omega_{\rm gw}/{\rm d}\ln f\approx 2/3$ generically produced by lower-redshift and less-massive BBHs. A detection of this unique flattening by the future O5 LIGO/Virgo would be a smoking gun of a high-chirp mass, high-redshift BBH population, as expected from PopIII stars. It would also constrain the PopIII initial mass function and star formation rate and the cosmic reionization history.
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We perform a measurement of the mass--richness relation of the redMaPPer galaxy cluster catalogue using weak lensing data from the Sloan Digital Sky Survey. We have carefully characterized a broad range of systematic uncertainties, including shear calibration errors, photo-$z$ biases, dilution by member galaxies, source obscuration, magnification bias, incorrect assumptions about cluster mass profiles, cluster centering, halo triaxiality, and projection effects. We also compare measurements of the lensing signal from two independently-produced shear and photometric redshift catalogues to characterize systematic errors in the lensing signal itself. Using a sample of 5,570 clusters from $0.1\le z\le 0.33$, the normalization of our power-law mass vs.\ $\lambda$ relation is $\log_{10}[M_{200m}/h^{-1}\ M_{\odot}]$ = $14.344 \pm 0.021$ (statistical) $\pm 0.023$ (systematic) at a richness $\lambda=40$, a 7 per cent calibration uncertainty, with a power-law index of $1.33^{+0.09}_{-0.10}$ ($1\sigma$). The detailed systematics characterization in this work renders it the definitive weak lensing mass calibration for SDSS redMaPPer clusters at this time.
We use the Millennium simulation to show that halo clustering varies significantly with cosmic web type. Halos are classified as node, filament, sheet and void halos based on the eigenvalue decomposition of the velocity shear tensor. This classification allows us to examine the clustering of halos as a function of web type in different mass ranges. We find that node halos show positive bias for all mass ranges probed, even for 10^11 and 10^12 Msun/h mass bins where the clustering of the entire halo sample is anti-biased. In all mass bins filament halos show negligible bias, whereas void and sheet halos are anti-biased. The zero-crossing of the void and sheet correlation functions occur at much smaller scales Mpc/h when compared to 5the same correlation functions for the entire halo sample. Our results suggest that the mass dependence of halo clustering is rooted in the composition of web types in the mass bin. The substantial fraction of node type halos for halo masses 2 x 10^13 Msun/h leads to positive bias. Filament type halos prevail at intermediate masses, 10^12-10^13 Msun/h, resulting in unbiased clustering. The large contribution of sheet type halos at low halo masses 10^12 Msun/h generates anti-biasing.
We investigate two dark energy cosmological models (i.e., the $\Lambda$CDM and $\phi$CDM models) with massive neutrinos in both the spatially flat and non-flat scenarios, where in the $\phi$CDM model the scalar field possesses an inverse power-law potential, $V(\phi)\propto {\phi}^{-\alpha}$ ($\alpha>0$). Cosmic microwave background data from Planck 2015, baryon acoustic oscillations data from 6dFGS, SDSS-MGS, BOSS-LOWZ and BOSS CMASS-DR11, the JLA compilation of Type Ia supernova apparent magnitude observations, and the Hubble Space Telescope $H_0$ prior, are jointly employed to constrain the model parameters. In the spatially flat (non-flat) $\Lambda$CDM model, the sum of neutrino masses is bounded as $\Sigma m_{\nu} < 0.166 (0.354)$ eV at 95\% confidence level (CL). Correspondingly, in the flat (non-flat) $\phi$CDM model, we find $\Sigma m_{\nu} < 0.164 (0.364)$ eV at 95\% CL. The inclusion of spatial curvature as a free parameter results in a significant broadening of confidence regions for $\Sigma m_{\nu}$ and other parameters. However, the curvature density parameter is constrained to $-0.0017 < \Omega_k < 0.0092$ for the $\Lambda$CDM model and $-0.0019 < \Omega_k < 0.0096$ for the $\phi$CDM model at 95\% CL, which is very close to zero.
Accretion shocks around galaxy clusters mark the position where the infalling diffuse gas is significantly slowed down, heated up, and becomes a part of the intracluster medium (ICM). They play an important role in setting the ICM properties. Hydrodynamical simulations have found an intriguing result that the radial position of this accretion shock tracks closely the position of the `splashback radius' of the dark matter, despite the very different physical processes that gas and dark matter experience. Using the self-similar spherical collapse model for dark matter and gas, we find that an alignment between the two radii happens only for a gas with an adiabatic index of $\gamma \approx 5/3$ and for clusters with moderate mass accretion rates. In addition, we find that some observed ICM properties, such as the entropy slope and the effective polytropic index lying around $\sim 1.1-1.2$, are captured by the self-similar spherical collapse model, and are insensitive to the mass accretion history.
Cold Dark Matter (CDM) models struggle to match the observations at galactic scales. The tension can be reduced either by dramatic baryonic feedback effects or by modifying the particle physics of CDM. Here, we consider an ultra-light scalar field DM particle manifesting a wave nature below a DM particle mass-dependent Jeans scale. For DM mass $m\sim10^{-22}{\rm eV}$, this scenario delays galaxy formation and avoids cusps in the center of the dark matter haloes. We use new measurements of half-light mass in ultra-faint dwarf galaxies Draco II and Triangulum II to estimate the mass of the DM particle in this model. We find that if the stellar populations are within the core of the density profile then the data are in agreement with a wave dark matter model having a DM particle with $m\sim 3.7-5.6\times 10^{-22}{\rm eV}$. The presence of this extremely light particle will contribute to the formation of a central solitonic core replacing the cusp of a Navarro-Frenk-White profile and bringing predictions closer to observations of cored central density in dwarf galaxies.
We present the results of N-body/smoothed particle hydrodynamics simulations of galaxy cluster collisions with a two component model of dark matter, which is assumed to consist of a predominant non-interacting dark matter component and a 20 percent mass fraction of dark plasma. Dark plasma is an intriguing form of interacting dark matter with an effective fluid-like behavior, which is well motivated by various theoretical particle physics models. We find that by choosing suitable simulation parameters, the observed distributions of dark matter in both the Bullet Cluster (1E 0657-558) and Abell 520 (MS 0451.5+0250) can be qualitatively reproduced. In particular, it is found that dark plasma forms an isolated mass clump in the Abell 520 system which cannot be explained by traditional models of dark matter, but has been detected in weak lensing observations.
We explore the possibility of planet formation in the carbon-rich protoplanetary disks of carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe. The chemically anomalous abundance patterns ([C/Fe] $\geq$ 0.7) in this subset of low-mass stars suggest pollution by primordial core-collapsing supernovae (SNe) ejecta that are particularly rich in carbon dust grains. By comparing the dust-settling timescale in the protoplanetary disks of CEMP stars to the expected disk lifetime (assuming dissipation via photoevaporation), we determine the maximum distance $r_{max}$ from the host CEMP star at which carbon-rich planetesimal formation is possible, as a function of the host star's [C/H] abundance. We then use our linear relation between $r_{max}$ and [C/H], along with the theoretical mass-radius relation derived for a solid, pure carbon planet, to characterize potential planetary transits across host CEMP stars. Given that the related transits are detectable with current and upcoming space-based transit surveys, we suggest initiating an observational program to search for carbon planets around CEMP stars in hopes of shedding light on the question of how early planetary systems may have formed after the Big Bang.
The typical optical-UV continuum slopes observed in many type 1 active galactic nuclei (AGN) are redder than expected from thin accretion disk models. A possible resolution to this conundrum is that many AGN are reddened by dust along the line of sight. To explore this possibility, we stack 5000 SDSS AGN with luminosity L ~ 10^45 erg/s and redshift z ~ 0.4 in bins of optical continuum slope alpha_opt and width of the broad Hbeta emission line. We measure the equivalent width (EW) of the NaID absorption feature in each stacked spectrum. We find a linear relation between alpha_opt and EW(NaID), such that EW(NaID) increases as alpha_opt becomes redder. In the bin with the smallest Hbeta width, objects with the bluest slopes that are similar to accretion disk predictions are found to have EW(NaID) = 0, supporting the line-of-sight dust hypothesis. This conclusion is also supported by the dependence of the Halpha/Hbeta line ratio on alpha_opt. The implied relationship between continuum slope and dust reddening is given by E(B-V) ~ 0.2(-0.1 - alpha_opt), and the implied reddening of a typical type 1 AGN with alpha_opt = -0.5 is E(B-V) ~ 0.08 mag. The relation between E(B-V) and NaI column is similar to the relation in the Milky-Way found in previous studies. Combining this fact with photoionization calculations, we argue that the line-of-sight dusty gas is the interstellar medium of the host galaxy, and that the sodium absorption arises in regions shielded from the AGN radiation, along the line of sight to the stars.
We study the Universe at the late stage of its evolution and deep inside the cell of uniformity. At such a scale the Universe is highly inhomogeneous and filled with discretely distributed inhomogeneities in the form of galaxies and groups of galaxies. As a matter source, we consider dark matter (DM) and dark energy (DE) with a non-linear interaction $Q = 3\mathcal{H}\gamma \overline\varepsilon_{\mathrm{DE}} \overline\varepsilon_{\mathrm{DM}} / (\overline\varepsilon_{\mathrm{DE}} + \overline\varepsilon_{\mathrm{DM}})$, where $\gamma$ is a constant. We assume that DM is pressureless and DE has a constant equation of state parameter $w$. In the considered model, the energy densities of the dark sector components present a scaling behaviour with $\overline\varepsilon_{\mathrm{DM}} / \overline\varepsilon_{\mathrm{DE}} \sim \left({a_0} / {a} \right)^{-3(w+\gamma)}$. We investigate the possibility that the perturbations of DM and DE, which are interacting among themselves, could be coupled to the galaxies with the former being concentrated around them. To carry our analysis, we consider the theory of scalar perturbations (within the mechanical approach), and obtain the sets of parameters $(w,\gamma)$ which do not contradict it. We conclude that two sets: $(w=-2/3,\gamma=1/3)$ and $(w=-1,\gamma=1/3)$ are of special interest. First, the energy densities of DM and DE on these cases are concentrated around galaxies confirming that they are coupled fluids. Second, we show that for both of them, the coincidence problem is less severe than in the standard $\Lambda$CDM. Third, the set $(w=-1,\gamma=1/3)$ is within the observational constraints. Finally, we also obtain an expression for the gravitational potential in the considered model.
Recent developments in searches for dark-matter candidates with atomic clocks are reviewed. The intended audience is the atomic clock community.
We present the simulation framework CRPropa version 3 designed for efficient development of astrophysical predictions for ultra-high energy particles. Users can assemble modules of the most relevant propagation effects in galactic and extragalactic space, include their own physics modules with new features, and receive on output primary and secondary cosmic messengers including nuclei, neutrinos and photons. In extension to the propagation physics contained in a previous CRPropa version, the new version facilitates high-performance computing and comprises new physical features such as an interface for galactic propagation using lensing techniques, an improved photonuclear interaction calculation, and propagation in time dependent environments to take into account cosmic evolution effects in anisotropy studies and variable sources. First applications using highlighted features are presented as well.
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We test the DARKexp model for relaxed, self-gravitating, collisionless systems against equilibrium dark matter halos from the Millennium-II simulation. While limited tests of DARKexp against simulations and observations have been carried out elsewhere, this is the first time the testing is done with a large sample of simulated halos spanning a factor of ~ 50 in mass, and using independent fits to density and energy distributions. We show that DARKexp, a one shape parameter family, provides very good fits to the shapes of density profiles, \rho(r), and differential energy distributions, N(E), of individual simulated halos. The best fit shape parameter $\phi_{0}$ obtained from the two types of fits are correlated, though with scatter. Our most important conclusions come from \rho(r) and N(E) that have been averaged over many halos. These show that the bulk of the deviations between DARKexp and individual Millennium-II halos come from halo-to-halo fluctuations, likely driven by substructure, and other density perturbations. The average \rho(r) and N(E) are quite smooth and follow DARKexp very closely. The only deviation that remains after averaging is small, and located at most bound energies for N(E) and smallest radii for \rho(r). Since the deviation is confined to 3-4 smoothing lengths, and is larger for low mass halos, it is likely due to numerical resolution effects.
We use a kinematic parametrisation of the luminosity distance to measure the angular distribution on the sky of time derivatives of the scale factor, in particular the Hubble parameter H_0, the deceleration parameter q_0 and the jerk parameter j_0. We apply the method introduced in Carvalho & Marques (2015) to complement probing the inhomogeneity of the large-scale structure by means of the inhomogeneity in the cosmic expansion. This parametrisation is independent of the cosmological equation of state, which renderes it adequate to test interpretations of the cosmic acceleration alternative to the cosmological constant. We also measure the anisotropy of the parameters by computing the power spectrum of the corresponding parameters' maps up to ell=3. Finally for an analytical toy model of an inhomogeneous ensemble of homogenous pixels, we derive the backreaction term in j_0 due to the fluctuations of {H_0,q_0} and measure it to be of order 0.01 the corresponding average over the pixels in the absence of backreaction. The backreaction effect on q_0 remains below the detection threshold, in agreement with that computed using a Lambda CDM parametrisation of the luminosity distance. Although the backreaction effect on j_0 is about 10 times that on q_0, it is also below the detection threshold. Hence backreaction remains unobservable both in q_0 and in j_0.
We investigate the dependency of Higgs inflation on the non-renormalisable matching between the low energy Standard Model limit and the inflationary regime at high energies. We show that for the top mass range $m_t \gtrsim 171.8$ GeV the scenario robustly predicts the spectral index $n_s \simeq 0.97$ and the tensor-to-scalar ratio $r\simeq 0.003$. The matching is however non-trivial, even the best-fit values $m_h=125.09$ GeV and $m_t=173.21$ GeV require a jump $\delta \lambda \sim 0.01$ in the Higgs coupling below the inflationary scale. For $m_t\lesssim 171.8$ GeV, the matching may generate a feature in the inflationary potential. In this case the predicted values of $n_s$ and $r$ vary but the model is still falsifiable. For example, a detection of negative running of spectral index at level $\alpha_s \lesssim -0.01$ would rule out Higgs inflation.
Radio observations over the last two decades have provided evidence that diffuse synchrotron emission in the form of megaparsec-scale radio halos in galaxy clusters is likely tracing regions of the intracluster medium where relativistic particles are accelerated during cluster mergers. In this paper we present results of a survey of 14 galaxy clusters carried out with the 7-element Karoo Array Telescope at 1.86 GHz, aimed to extend the current studies of radio halo occurrence to systems with lower masses (M$_{\rm 500} > 4\times10^{14}$ M${_\odot}$). We found upper limits at the $0.6 - 1.9 \times 10^{24}$ Watt Hz$^{-1}$ level for $\sim 50\%$ of the sample, confirming that bright radio halos in less massive galaxy clusters are statistically rare.
The LaSilla/QUEST Variability Survey (LSQ) and the Carnegie Supernova Project (CSP II) are collaborating to discover and obtain photometric light curves for a large sample of low redshift (z < 0.1) Type Ia supernovae. The supernovae are discovered in the LSQ survey using the 1 m ESO Schmidt telescope at the La Silla Observatory with the 10 square degree QUEST camera. The follow-up photometric observations are carried out using the 1 m Swope telescope and the 2.5 m du Pont telescopes at the Las Campanas Observatory. This paper describes the survey, discusses the methods of analyzing the data and presents the light curves for the first 31 Type Ia supernovae obtained in the survey. The SALT 2.4 supernova light curve fitter was used to analyze the photometric data, and the Hubble diagram for this first sample is presented. The measurement errors for these supernovae averaged 4%, and their intrinsic spread was 14%.
We present the Red-sequence Cluster Lensing Survey (RCSLenS), an application
of the methods developed for the Canada France Hawaii Telescope Lensing Survey
(CFHTLenS) to the ~785deg$^2$, multi-band imaging data of the Red-sequence
Cluster Survey 2 (RCS2). This project represents the largest public,
sub-arcsecond seeing, multi-band survey to date that is suited for weak
gravitational lensing measurements. With a careful assessment of systematic
errors in shape measurements and photometric redshifts we extend the use of
this data set to allow cross-correlation analyses between weak lensing
observables and other data sets. We describe the imaging data, the data
reduction, masking, multi-colour photometry, photometric redshifts, shape
measurements, tests for systematic errors, and a blinding scheme to allow for
more objective measurements. In total we analyse 761 pointings with r-band
coverage, which constitutes our lensing sample. Residual large-scale B-mode
systematics prevent the use of this shear catalogue for cosmic shear science.
The effective number density of lensing sources over an unmasked area of
571.7deg$^2$ and down to a magnitude limit of r~24.5 is 8.1 galaxies per
arcmin$^2$ (weighted: 5.5 arcmin$^{-2}$) distributed over 14 patches on the
sky. Photometric redshifts based on 4-band griz data are available for 513
pointings covering an unmasked area of 383.5 deg$^2$ We present weak lensing
mass reconstructions of some example clusters as well as the full survey
representing the largest areas that have been mapped in this way. All our data
products are publicly available through CADC at
this http URL
in a format very similar to the CFHTLenS data release.
We measure the cross-correlation signature between the Planck CMB lensing map and the weak lensing observations from both the Red-sequence Cluster Lensing Survey (RCSLenS) and the Canada-France-Hawai Telescope Lensing Survey (CFHTLenS). In addition to a Fourier analysis, we include the first configuration-space detection, based on the estimators $\langle \kappa_{\rm CMB} \kappa_{\rm gal} \rangle$ and $\langle \kappa_{\rm CMB} \gamma_{t} \rangle$. Combining 747.2 deg$^2$ from both surveys, we find a detection significance that exceeds $4.2\sigma$ in both Fourier- and configuration-space analyses. Scaling the predictions by a free parameter $A$, we obtain $A^{\rm Planck}_{\rm CFHT}= 0.68\pm 0.31 $ and $A^{\rm Planck}_{\rm RCS}= 1.31\pm 0.33$. In preparation for the next generation of measurements similar to these, we quantify the impact of different analysis choices on these results. First, since none of these estimators probes the exact same dynamical range, we improve our detection by combining them. Second, we carry out a detailed investigation on the effect of apodization, zero-padding and mask multiplication, validated on a suite of high-resolution simulations, and find that the latter produces the largest systematic bias in the cosmological interpretation. Finally, we show that residual contamination from intrinsic alignment and the effect of photometric redshift error are both largely degenerate with the characteristic signal from massive neutrinos, however the signature of baryon feedback might be easier to distinguish. The RCSLenS lensing data are now publicly available.
We present a new approximation to include fully general relativistic pressure and velocity in Newtonian hydrodynamics. The energy conservation, momentum conservation and two Poisson's equations are consistently derived from Einstein's gravity in the zero-shear gauge assuming weak gravity and action-at-a-distance limit. The equations show proper special relativity limit in the absence of gravity. Our approximation is complementary to the post-Newtonian approximation and the equations are valid in fully nonlinear situations.
Deep observations of galaxies reveal faint extended stellar components (hereafter ESCs) of streams, shells, and halos. These are a natural prediction of hierarchical galaxy formation, as accreted satellite galaxies are tidally disrupted by their host. We investigate whether or not global properties of the ESC could be used to test of dark matter, reasoning that they should be sensitive to the abundance of low-mass satellites, and therefore the underlying dark matter model. Using cosmological simulations of galaxy formation in the favoured Cold Dark Matter (CDM) and Warm Dark Matter (WDM) models ($m_{\rm WDM}$=0.5,1,2 keV/$c^2$), which suppress the abundance of low-mass satellites, we find that the kinematics and orbital structure of the ESC is consistent across models. However, we find striking differences in its spatial structure, as anticipated -- a factor of $\sim$10 drop in spherically averaged mass density between $\sim$10% and $\sim$75% of the virial radius in the more extreme WDM runs ($m_{\rm WDM}$=0.5, 1 keV/$c^2$) relative to the CDM run. These differences are consistent with the mass assembly histories of the different components, and are present across redshifts. However, even the least discrepant of the WDM models is incompatible with current observational limits on $m_{\rm WDM}$. Importantly, the differences we observe when varying the underlying dark matter are comparable to the galaxy-to-galaxy variation we expect within a fixed dark matter model. This suggests that it will be challenging to place limits on dark matter using only the unresolved spatial structure of the the ESC.
Based on a new kind of complementary principle, we describe physics concerning the cosmological constant problem in the framework of effective field theory and suggest that a dominant part of dark energy can originate from the zero point energy due to another graviton that performs a complementary role vis-a-vis the ordinary one and obtains a tiny mass through the coupling to the vacuum energy of matters.
We show that the observation of old strange quark stars (SQSs) can set important limits on the scattering cross sections $\sigma_q$ between the light quarks and the bosonic non-interacting dark matter (DM). By analyzing $1403$ sets of solitary pulsarlike compact stars in the Milky Way and converting the $\sigma_q$ into the DM-proton scattering cross sections $\sigma_p$ based on the effective operator analyses, we find the resulting $\sigma_p$ limit from the old SQSs could be comparable with that of the current direct detection experiments but much weaker (by several orders of magnitude) than that obtained from the old neutron stars (NSs), which requires an extremely small $\sigma_p$ far beyond the limits of direct detection experiments. Our findings imply that the old pulsars are favored to be SQSs rather than NSs if the bosonic DM were observed by future terrestrial experiments.
Spectral distortions of the Cosmic Microwave Background (CMB) offer the possibility of probing processes which occurred during the evolution of our Universe going back up to Z$\simeq 10^7$. Unfortunately all the attempts so far carried out for detecting distortions failed. All of them were based on comparisons among absolute measurements of the CMB temperature at different frequencies. We suggest a different approach: measurements of the frequency derivative of the CMB temperature over large frequency intervals instead of observations of the absolute temperature at few, well separated, frequencies as frequently done in the past. The best observing conditions can be found in space. We discuss therefore the perspectives of new observations in the next years from the ground, at very special sites, and in space as independent missions or as part of other CMB projects
We introduce a double power series method for finding approximate analytical
solutions for systems of differential equations commonly found in cosmological
perturbation theory. The method was set out, in a non-cosmological context, by
Feshchenko, Shkil' and Nikolenko (FSN) in 1966, and is applicable to cases
where perturbations are on sub-horizon scales. The FSN method is essentially an
extension of the well known Wentzel-Kramers-Brillouin (WKB) method for finding
approximate analytical solutions for ordinary differential equations. The FSN
method is well suited for solving systems of linear second order ordinary
differential equations, that also depend on a small parameter, which here we
take to be the inverse wave-number.
We use the FSN method to find new approximate oscillating solutions in linear
order cosmological perturbation theory for a flat radiation-matter universe.
Together with this model's well known growing and decaying M\'esz\'aros
solutions, these oscillating modes provide a complete set of sub-horizon
approximations for the metric potential, radiation and matter perturbations.
Comparison with numerical solutions of the perturbation equations shows that
our approximations can be made accurate to within a typical error of 1%, or
better. We also set out a heuristic method for error estimation. A Mathematica
notebook which implements the double power series method is made available
online.
We study a Higgs inflation model with a running kinetic term, taking account of the renormalization group evolution of relevant coupling constants. Specifically we study two types of the running kinetic Higgs inflation, where the inflaton potential is given by the quadratic or linear term potential in a frame where the Higgs field is canonically normalized. We solve the renormalization group equations at two-loop level and calculate the scalar spectral index and the tensor-to-scalar ratio. We find that, even if the renormalization group effects are included, the quadratic inflation is ruled out by the CMB observations, while the linear one is still allowed.
Cosmological solutions derived by Nariai and Tomita (1971) and by Starobinsky (1980) are compared, and it is shown that the former derived de Sitter expansion in the R^2 modified gravity (without cosmological constant) at the earliest stage, and nine years later the latter derived the well-known inflationary solution. Next the property of their simplified models is described using the method of conformal transformations, and how the inflation arises and the singularity is avoided is shown. Finally the initial and final states of the inflation are discussed.
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