We present a new model-independent strategy for testing the Friedmann-Lema\^{\i}tre-Robertson-Walker metric and constraining cosmic curvature, based on future time delay measurements of strongly lensed quasar-elliptical galaxy systems from the Large Synoptic Survey Telescope and supernova observations from the Dark Energy Survey. The test only relies on geometric optics. It is independent of the energy contents of the universe and the validity of the Einstein equation on cosmological scales. The study comprises two levels: testing the FLRW metric through the Distance Sum Rule and determining/constraining cosmic curvature. We propose an effective and efficient (redshift) evolution model for performing the former test, which allows us to concretely specify the violation criterion for the FLRW Distance Sum Rule. If the FLRW metric is consistent with the observations, then, on the second level, the cosmic curvature parameter will be constrained to $\sim0.057$ or $\sim0.041$ ($1\sigma$), depending on the availability of high-redshift supernovae, much more stringent than current model-independent techniques. We also show that the bias in the time delay method might be well controlled, leading to robust results. The proposed method is a new independent tool for both testing the fundamental assumptions of homogeneity and isotropy in cosmology and for determining cosmic curvature. It is complementary to cosmic microwave background plus baryon acoustic oscillation analyses, which normally assume a cosmological model with dark energy domination in the late-time universe.
Galaxy groups and clusters are the main tools used to test cosmological
models and to study the environmental effect of galaxy formation. This work
provides a catalogue of galaxy groups and clusters, as well as potentially
merging systems based on the SDSS main galaxy survey. We identified galaxy
groups and clusters using the modified friends-of-friends (FoF) group finder
designed specifically for flux-limited galaxy surveys. The FoF group membership
is refined by multimodality analysis to find subgroups and by using the group
virial radius and escape velocity to expose unbound galaxies. We look for
merging systems by comparing distances between group centres with group radii.
The analysis results in a catalogue of 88662 galaxy groups with at least two
members. Among them are 6873 systems with at least six members which we
consider to be more reliable groups. We find 498 group mergers with up to six
groups. We performed a brief comparison with some known clusters in the nearby
Universe, including the Coma cluster and Abell 1750. The Coma cluster in our
catalogue is a merging system with six distinguishable subcomponents. In the
case of Abell 1750 we find a clear sign of filamentary infall toward this
cluster. Our analysis of mass-to-light ratio (M/L) of galaxy groups reveals
that M/L slightly increases with group richness.
We consider a multi-field inflationary model with two real scalar fields. The solitons of this model are field configurations that have the form of closed loops in the field space. We study the formation and evolution of these solitons, in particular, the conditions at which they could be formed even when the model potential has only one minimum in the field space. These non-trivial field configurations represent planar domain walls in the three-dimensional physical space. The set of these configurations can be split into disjoint equivalence classes. We provide a simple expression for the winding number of an arbitrary closed loop in the field space and discuss the transitions that change the winding number.
Memory effects of gravitational waves from astronomical events or primordial universe might have the information of new physics. It is intriguing to observe that the memory effect exists in electrodynamics as a net momentum kick, while the memory effect in gravity appears as a net relatively displacement. In particular, Winicour has shown that the B-mode memory, which characterizes parity odd global distribution of memory, does not exist. We study the memory effect in axion electrodynamics and find that the B-mode memory effect can exist provided the existence of coherently oscillating axion background field. Moreover, we examine the detectability of the axion dark matter using this effect. We also argue the existence of the B-mode gravitational memory effect in the presence of the axion dark matter.
We present a model that elucidates why gas depletion times in galaxies are long compared to the time scales of the processes driving the evolution of the interstellar medium. We show that global depletion times are not set by any "bottleneck" in the process of gas evolution towards the star-forming state. Instead, depletion times are long because star-forming gas converts only a small fraction of its mass into stars before it is dispersed by dynamical and feedback processes. Thus, complete depletion requires that gas transitions between star-forming and non-star-forming states multiple times. Our model does not rely on the assumption of equilibrium and can be used to interpret trends of depletion times with the properties of observed galaxies and the parameters of star formation and feedback recipes in galaxy simulations. In particular, the model explains the mechanism by which feedback self-regulates star formation rate in simulations and makes it insensitive to the local star formation efficiency. We illustrate our model using the results of an isolated $L_*$-sized disk galaxy simulation that reproduces the observed Kennicutt-Schmidt relation for both molecular and atomic gas. Interestingly, the relation for molecular gas is close to linear on kiloparsec scales, even though a non-linear relation is adopted in simulation cells. This difference is due to stellar feedback, which breaks the self-similar scaling of the gas density PDF with the average gas surface density.
We present a comprehensive analysis of the spin temperature/covering factor degeneracy, T/f, in damped Lyman-alpha absorption systems. By normalising the upper limits and including these via a survival analysis, there is, as previously claimed, an apparent increase in T/f with redshift at z > 1. However, when we account for the geometry effects of an expanding Universe, neglected by the previous studies, this increase in T/f at z > 1 is preceded by a decrease at z < 1. Using high resolution radio images of the background continuum sources, we can transform the T/f degeneracy to T/d^2, where d is the projected linear size of the absorber. Again, there is no overall increase with redshift, although a dip at z ~ 2 persists. Furthermore, we find d^2/T to follow a similar variation with redshift as the star formation rate. This suggests that, although the total hydrogen column density shows little relation to the SFR, the fraction of the cold neutral medium may. Therefore, further efforts to link the neutral gas with the star formation history should also consider the cool component of the gas.
Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation Chinese radio telescopes through a blind searching of 21-cm absorption systems. We forecast the capabilities of surveys of 21-cm absorption systems by two representative radio telescopes in China -- Five-hundred-meter Aperture Spherical radio Telescope (FAST) and Tianlai 21-cm cosmology experiment (Tianlai). Facilitated by either the high sensitivity (FAST) or the wide field of view (Tianlai) of these telescopes, more than a thousand 21-cm absorption systems can be discovered in a few years, representing orders of magnitude improvement over the cumulative discoveries in the past half a century.
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We demonstrate that, for the baseline design of the CORE satellite mission, the polarized foregrounds can be controlled at the level required to allow the detection of the primordial cosmic microwave background (CMB) $B$-mode polarization with the desired accuracy at both reionization and recombination scales, for tensor-to-scalar ratio values of $r\gtrsim 5\times 10^{-3}$. Under the assumption of perfect control of lensing effects, CORE would measure an unbiased estimate of $r=5\times 10^{-3}$ with an uncertainty of ${\sigma(r=5\times 10^{-3})=0.4\times 10^{-3}}$ after foreground cleaning. In presence of both gravitational lensing effects and astrophysical foregrounds, the significance of the detection is lowered, with CORE achieving yet a $4\sigma$-measurement of $r=5\times 10^{-3}$ after foreground cleaning and $60$% delensing. We deliberately consider detailed sky simulations based on state-of-the-art CMB observations that consist of CMB polarization with $\tau=0.055$ and tensor-to-scalar values ranging from $r=10^{-2}$ to $10^{-3}$, Galactic synchrotron and thermal dust polarization with variable spectral indices over the sky, polarized anomalous microwave emission, polarized infrared and radio sources, and gravitational lensing effects. Using both parametric and blind approaches, we perform the full component separation and likelihood analysis of the simulations, allowing us to quantify both uncertainties and biases on the reconstructed primordial $B$-modes. We report two sources of potential bias for the detection of the primordial B-modes by future CMB experiments: (i) incorrect foreground models, (ii) averaging of foreground spectral indices by pixellization and beam convolution.
We revisit the constraints on inflation models by using the current cosmological observations involving the latest local measurement of Hubble constant ($H_{0} = 73.00\pm 1.75$ km s $^{-1}$ Mpc$^{-1}$). We constrain the primordial power spectra of both scalar and tensor perturbations with the observational data including the Planck 2015 CMB full data, the BICEP2 and Keck Array CMB B-mode data, the BAO data, and the direct measurement of $H_0$. In order to relieve the tension between the local determination of Hubble constant and the other astrophysical observations, we consider the additional parameter $N_{\rm eff}$ in the cosmological model. We find that, for the $\Lambda$CDM+$r$+$N_{\rm eff}$ model, the scale invariance is only excluded at the 3.3$\sigma$ level, and $\Delta N_{\rm eff}>0$ is favored at the 1.6$\sigma$ level. Comparing the obtained 1$\sigma$ and 2$\sigma$ contours of $(n_s,r)$ with the theoretical predictions of selected inflation models, we find that both the convex and concave potentials are favored at 2$\sigma$ level, the natural inflation model is excluded at more than 2$\sigma$ level, the Starobinsky $R^2$ inflation model is only favored at around 2$\sigma$ level, and the spontaneously broken SUSY inflation model is now the most favored model.
We propose a new realization of strongly interacting massive particles (SIMP) as self-interacting dark matter, where SIMPs couple to the Standard Model sector through an axion-like particle. Our model gets over major obstacles accompanying the original SIMP model, such as a missing mechanism of kinetically equilibrating SIMPs with the SM plasma as well as marginal perturbativity of the chiral Lagrangian density. Remarkably, the parameter region realizing $\sigma_{\rm self}/m_{\rm DM} \simeq 0.1 \textrm{--} 1 \, {\rm cm}^{2}/{\rm g}$ is within the reach of future beam dump experiments such as the Search for Hidden Particles (SHiP) experiment.
A new understanding of dark matter stability is pointed out, based on the simplest spontaneously broken Abelian $U(1)$ gauge model with one complex scalar and one Dirac fermion. The key is the imposition of dark charge conjugation symmetry. It allows the possible existence of two stable particles: the Dirac fermion and the vector gauge boson which acts as a light mediator for the former's self-interaction. Since this light mediator does not decay, it avoids the strong cosmological constraints recently obtained for all such models where the light mediator decays into standard-model particles.
Extending the work of Ferrara and one of the authors, we present dynamical cosmological models of $\alpha$-attractors with plateau potentials for $3\alpha=1,2,3,4,5,6,7$. These models are motivated by geometric properties of maximally supersymmetric theories: M-theory, superstring theory, and maximal $N = 8$ supergravity. After a consistent truncation of maximal to minimal supersymmetry in a seven-disk geometry, we perform a two-step procedure: 1) we introduce a superpotential, which stabilizes the moduli of the seven-disk geometry in a supersymmetric minimum, 2) we add a cosmological sector with a nilpotent stabilizer, which breaks supersymmetry spontaneously and leads to a desirable class of cosmological attractor models. These models with $n_s$ consistent with observational data, and with tensor-to-scalar ratio $r \approx 10^{-2}- 10^{-3}$, provide natural targets for future B-mode searches. We relate the issue of stability of inflationary trajectories in these models to tessellations of a hyperbolic geometry.
If the electroweak sector of the standard model is described by classically conformal dynamics, the early universe evolution can be substantially altered. It is already known that---contrarily to the standard model case---a first order electroweak phase transition may occur. Here we show that, depending on the model parameters, a dramatically different scenario may happen: A first-order, six massless quarks QCD phase transition occurs first, which then triggers the electroweak symmetry breaking. We derive the necessary conditions for this dynamics to occur, using the specific example of the classically conformal B-L model. In particular, relatively light weakly coupled particles are predicted, with implications for collider searches. This scenario is also potentially rich in cosmological consequences, such as renewed possibilities for electroweak baryogenesis, altered dark matter production, and gravitational wave production, as we briefly comment upon.
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This is an ongoing review on the brief history of the scalar field dark matter model also known as fuzzy dark matter, BEC dark matter, wave dark matter, or ultra-light axion. In this model ultra-light scalar dark matter particles with mass $m = O(10^{-22})eV$ condense in a single Bose-Einstein condensate state and behave collectively like a classical wave. Galactic dark matter halos can be described as a self-gravitating coherent scalar field configuration called boson stars. At the scale larger than galaxies the dark matter acts like cold dark matter, while below the scale quantum pressure from the uncertainty suppresses the smaller structure formation so that it can resolve the problems of the conventional cold dark matter model.
This work explores the ability of computer vision algorithms to characterise dark matter haloes formed in different models of structure formation. We produce surface mass density maps of the most massive haloes in a suite of eight numerical simulations, all based on the same initial conditions, but implementing different models of gravity. This suite includes a standard $\Lambda$CDM model, two variations of $f(R)$-gravity, two variations of Symmetron gravity and three Dvali, Gabadadze and Porrati (DGP) models. We use the publicly available WND-CHARM algorithm to extract 2919 image features from either the raw pixel intensities of the maps, or from a variety of image transformations including Fourier, Wavelet, Chebyshev and Edge transformations. After discarding the most degenerate models, we achieve more than 60% single-image classification success rate in distinguishing the four different models of gravity while using a simple weighted neighbour distance (WND) to define our classification metric. This number can be increased to more than 70% if additional information, such as a rough estimate of the halo mass, is included. We find that the classification success steeply declines when the noise level in the images is increased, but that this trend can be largely reduced by smoothing the noisy data. We find Zernike moments of the Fourier transformation of either the raw image or its Wavelet transformation to be the most descriptive feature, followed by the Gini coefficient of several transformations and the Haralick and Tamura textures of the raw pixel data eventually pre-processed by an Edge transformation. The proposed methodology is general and does not only apply to the characterisation of modified gravity models, but can be used to classify any set of models which show variations in the 2D morphology of their respective structure.
Existing theoretical and observational constraints on the abundance of magnetic monopoles are limited. Here we demonstrate that an ensemble of monopoles forms a plasma whose properties are well determined and whose collective effects place new tight constraints on the cosmological abundance of monopoles. In particular, the existence of micro-Gauss magnetic fields in galaxy clusters and radio relics implies that the scales of these structures are below the Debye screening length, thus setting an upper limit on the cosmological density parameter of monopoles, $\Omega_M\lesssim3\times10^{-4}$, which precludes them from being the dark matter. Future detection of Gpc-scale coherent magnetic fields could improve this limit by a few orders of magnitude. In addition, we predict the existence of magnetic Langmuir waves and turbulence which may appear on the sky as "zebra patterns" of an alternating magnetic field with ${\bf k\cdot B}\not=0$. We also show that magnetic monopole Langmuir turbulence excited near the accretion shock of galaxy clusters may be an efficient mechanism for generating the observed intracluster magnetic fields.
Direct detection of regions of ionized hydrogen (HII) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, low-frequency radio interferometers. We investigate the feasibility of combining low-frequency observations with the Square Kilometre Array and near infra-red survey data of the Wide-Field Infrared Survey Telescope to detect cosmic reionization by imaging HII bubbles surrounding massive galaxies during the cosmic dawn. While individual bubbles will be too small to be detected, we find that by stacking redshifted 21-cm spectra centred on known galaxies, it will be possible to directly detect the EoR at $z \sim 9-12$, and to place qualitative constraints on the evolution of the spin temperature of the intergalactic medium (IGM) at $z \geq 9$. In particular, given a detection of ionized bubbles using this technique, it is possible to determine if the IGM surrounding them is typically in absorption or emission. Determining the globally-averaged neutral fraction of the IGM using this method will prove more difficult due to degeneracy with the average size of HII regions.
The use of Eulerian 'standard perturbation theory' to describe mass assembly in the early universe has traditionally been limited to modes with k $\lesssim$ 0.1 h/Mpc at z = 0. At larger k the SPT power spectrum deviates from measurements made using N-body simulations. Recently, there has been progress in extending the reach of perturbation theory to larger k using ideas borrowed from effective field theory. We revisit the computation of the redshift-space matter power spectrum within this framework, including for the first time the full one-loop time dependence. We use a resummation scheme proposed by Vlah et al. to account for damping of baryonic acoustic oscillations due to large-scale random motions and show that this has a significant effect on the multipole power spectra. We renormalize by comparison to a suite of custom N-body simulations matching the MultiDark MDR1 cosmology. At z = 0 and for scales k $\lesssim$ 0.4 h/Mpc we find that the EFT furnishes a description of the real-space power spectrum up to $\sim$2%, for the $\ell$ = 0 mode up to $\sim$5%, and for the $\ell$ = 2, 4 modes up to $\sim$25%. We argue that, in the MDR1 cosmology, positivity of the $\ell$ = 0 mode gives a firm upper limit of k $\approx$ 0.75 h/Mpc for the validity of the one-loop EFT prediction in redshift space using only the lowest-order counterterm. We show that replacing the one-loop growth factors by their Einstein-de Sitter counterparts is a good approximation for the $\ell$ = 0 mode, but can induce deviations as large as 2% for the $\ell$ = 2, 4 modes. An accompanying software bundle, distributed under open source licenses, includes Mathematica notebooks describing the calculation, together with parallel pipelines capable of computing both the necessary one-loop SPT integrals and the effective field theory counterterms.
Strong gravitational lensing by galaxy clusters is a fundamental tool to study dark matter and constrain the geometry of the Universe. Recently, the HST Frontier Fields program has allowed a significant improvement of mass and magnification measurements but lensing models still have a residual RMS between 0.2" and few arcseconds, not yet completely understood. Systematic errors have to be better understood and treated in order to use strong lensing clusters as reliable cosmological probes. We have analysed two simulated Hubble Frontier Fields-like clusters from the Hubble Frontier Fields Comparison Challenge, Ares and Hera. We use several estimators (relative bias on magnification, density profiles, ellipticity and orientation) to quantify the goodness of our reconstructions by comparing our multiple models, optimized with the parametric software Lenstool, with the input models. We have quantified the impact of systematic errors arising, first, from the choice of different density profiles and configurations and, secondly, from the availability of constraints (spectroscopic or photometric redshifts, redshift ranges of the background sources) in the parametric modelling of strong lensing galaxy clusters and therefore on the retrieval of cosmological parameters. We find that substructures in the outskirts have a significant impact on the position of the multiple images, yielding tighter cosmological contours. The need for wide-field imaging around massive clusters is thus reinforced. We show that competitive cosmological constraints can be obtained also with complex multimodal clusters and that photometric redshifts improve the constraints on cosmological parameters when considering a narrow range of (spectroscopic) redshifts for the sources.
Small evaporating black holes were suggested to be dangerous inducing fast decay of the electroweak false vacuum. We find that the flat-spectrum matter perturbations growing at the post-inflationary matter dominated stage can produce such black holes in a tiny yet sufficient amount to destroy the vacuum in the visible part of the Universe via the induced process. This observation gives one more cosmological argument for the need of new physics in the Higgs sector. If no suitable modification is introduced, the absence of small black holes in the early Universe imposes severe constraints on inflation and subsequent stages, which we outline. Since many well-motivated models (e.g. the R^2-inflation) are excluded by this observation, the original process of black hole-induced vacuum decay should be critically analyzed, and we end up questioning this effect.
We develop a hybrid formalism suitable for modeling scalar field dark matter, in which the phase-space distribution associated to the real scalar field is modeled by statistical equal-time two-point functions and gravity is treated by two stochastic gravitational fields in the longitudinal gauge (in this work we neglect vector and tensor gravitational perturbations). Inspired by the commonly used Newtonian Vlasov-Poisson system, we firstly identify a suitable combination of equal-time two-point functions that defines the phase-space distribution associated to the scalar field and then derive both a kinetic equation that contains relativistic scalar matter corrections as well as linear gravitational scalar field equations whose sources can be expressed in terms of a momentum integral over the phase-space distribution function. Our treatment generalizes the commonly used classical scalar field formalism, in that it allows for modeling of (dynamically generated) vorticity and perturbations in anisotropic stresses of the scalar field. It also allows for a systematic inclusion of relativistic and higher order corrections that may be used to distinguish different dark matter scenarios. We also provide initial conditions for the statistical equal-time two-point functions of the matter scalar field in terms of gravitational potentials and the scale factor.
We study all translationally and rotationally invariant local theories involving massless spin 2 and spin 1 particles that mediate long range forces, allowing for general energy relations and violation of boost invariance. Although gauge invariance is not a priori required to describe non Lorentz invariant theories, we first establish that locality requires `soft gauge invariance'. Then by taking the soft graviton limit in scattering amplitudes, we prove that in addition to the usual requirement of universal graviton couplings, the special relativistic energy-momentum relation is also required and must be exact. We contrast this to the case of theories with only spin $\leq1$ particles, where, although we can still derive charge conservation from locality, special relativity can be easily violated. We provide indications that the entire structure of relativity can be built up from spin 2 in this fashion.
We look at particle production by a homogenous electric field \'a la Schwinger mechanism in an expanding, flat de Sitter patch relevant for the inflationary epoch of our universe. Defining states and particle content in curved spacetime is certainly not a unique process. There being different line of thoughts on how to do that, we have used the Schr\"odinger formalism to define instantaneous particle content, classicality of the state etc. This allows us to go past the adiabatic regime to which the effect has been restricted in the previous studies and bring out its multifaceted nature in different settings. Each of these gives rise to contrasting features and behaviour as per the effect of electric field and expansion rate on the mean particle number. We notice that on increasing the strength of electric field there is actually a suppression of the particle creation over what occurs if we just had a pure de Sitter background. We also quantify the degree of classicality of the process during its evolution using a "classicality parameter" constructed out of parameters of the Wigner function. It turns out to be hit-and-miss in giving information about the quantum to classical transition but surely points to the need of performing a more robust study of the said transition in this case.
The process of superradiance can extract angular momentum and energy from astrophysical black holes (BHs) to populate gravitationally-bound states with an exponentially large number of light bosons. We analytically calculate superradiant growth rates for vectors around rotating BHs in the regime where the vector Compton wavelength is much larger than the BH size. Spin-1 bound states have superradiance times as short as a second around stellar BHs, growing up to a thou- sand times faster than their spin-0 counterparts. The fast rates allow us to use measurements of rapidly spinning BHs in X-ray binaries to exclude a wide range of masses for weakly-coupled spin-1 particles, $5 \times 10^{-14} - 2 \times 10^{-11}$ eV; lighter masses in the range $6 \times 10^{-20} - 2 \times 10^{-17}$ eV start to be constrained by supermassive BH spin measurements at a lower level of confidence. We also explore routes to detection of new vector particles possible with the advent of gravitational wave (GW) astronomy. The LIGO-Virgo collaboration could discover hints of a new light vector particle in statistical analyses of masses and spins of merging BHs. Vector annihilations source continuous monochromatic gravitational radiation which could be observed by current GW observatories. At design sensitivity, Advanced LIGO may measure up to thousands of annihilation signals from within the Milky Way, while hundreds of BHs born in binary mergers across the observable universe may superradiate vector bound states and become new beacons of monochromatic gravitational waves.
The CIBER collaboration released their first observational data of the Cosmic IR background (CIB) radiation, which has significant excesses at around the wavelength $\sim$ 1 $\mu$m compared to theoretically-inferred values. The amount of the CIB radiation has a significant influence on the opaqueness of the Universe for TeV gamma-rays emitted from distant sources such as AGNs. With the value of CIB radiation reported by the CIBER experiment, through the reaction of such TeV gamma-rays with the CIB photons, the TeV gamma-rays should be significantly attenuated during propagation, which would lead to energy spectra in disagreement with current observations of TeV gamma ray sources. In this article, we discuss a possible resolution of this tension between the TeV gamma-ray observations and the CIB data in terms of axion [or Axion-Like Particles (ALPs)] that may increase the transparency of the Universe by the anomaly-induced photon-axion mixing. We find a region in the parameter space of the axion mass, $m_a \sim 5 \times 10^{-10} - 3 \times 10^{-7}$eV, and the axion-photon coupling constant, $1.2 \times 10^{-11} {\rm GeV}^{-1} \lesssim g_{a\gamma} \lesssim 8.8 \times 10^{-10} {\rm GeV}^{-1}$ that solves this problem.
The kinematic dispersions of disc stars can be used to measure the dynamic contributions of baryons to the rotation curves of spiral galaxies and hence to trace the amount and distribution of the remaining dark matter. However, the simple single-component infinite disc model traditionally used to convert stellar dispersions to mass-densities is no longer adequate. The dark matter halo has a significant effect upon the stellar dispersions for any non-maximal disc. The correction for cuspy dark matter halos is particularly large, suggesting that such models are not consistent with the observed stellar dispersions. When a more realistic model for the vertical gravity of the disc is used, the derived stellar surface densities are generally larger (smaller) for disc radii smaller (larger) than 2.3 times the radial scale-length. When the vertical gravity correction is applied to the radially resolved stellar mass-to-light ratios derived by the DiskMass consortium, the true values are not constant but decrease with radius, as expected from photometric colour gradients, and the true mass scale-lengths are about 80% of the photometric scale-lengths. The effects of a thin gaseous disc are larger than expected, especially when an allowance is made for optically thick or CO-dark gas. The presence of a thick-disc stellar component has severe consequences, particularly if its radial scale-length is smaller than that of the thin disc, as it appears to be in the Milky Way.
We study dark matter production in scenarios where a scale invariant hidden sector interacts with the Standard Model degrees of freedom via a Higgs portal $\lambda \Phi^\dagger\Phi s^2$. If the hidden sector is very weakly coupled to the SM but exhibits strong interactions within its own particle species, the dark matter abundance may arise as a result of a dark freeze-out occurring in the hidden sector. Because of scale invariance, the free parameters in the hidden sector are determined and the dark matter candidate exhibits a 'WIMP miracle of the second kind'. Demonstrating the predictive power of scale invariance, we carry out thorough analysis of dark matter production in several benchmark scenarios where the hidden sector contains either a scalar, fermion (sterile neutrino), or vector dark matter, and discuss the observational consequences of these scenarios.
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We discuss the effects on the CMB, CIB, and thermal SZ effect due to the peculiar motion of an observer with respect to the CMB rest frame, which induces boosting effects. We investigate the scientific perspectives opened by future CMB space missions, focussing on the CORE proposal. The improvements in sensitivity offered by a mission like CORE, together with its high resolution over a wide frequency range, will provide a more accurate estimate of the CMB dipole. The extension of boosting effects to polarization and cross-correlations will enable a more robust determination of purely velocity-driven effects that are not degenerate with the intrinsic CMB dipole, allowing us to achieve a S/N ratio of 13; this improves on the Planck detection and essentially equals that of an ideal cosmic-variance-limited experiment up to a multipole l of 2000. Precise inter-frequency calibration will offer the opportunity to constrain or even detect CMB spectral distortions, particularly from the cosmological reionization, because of the frequency dependence of the dipole spectrum, without resorting to precise absolute calibration. The expected improvement with respect to COBE-FIRAS in the recovery of distortion parameters (in principle, a factor of several hundred for an ideal experiment with the CORE configuration) ranges from a factor of several up to about 50, depending on the quality of foreground removal and relative calibration. Even for 1% accuracy in both foreground removal and relative calibration at an angular scale of 1 deg, we find that dipole analyses for a mission like CORE will be able to improve the recovery of the CIB spectrum amplitude by a factor of 17 in comparison with current results based on FIRAS. In addition to the scientific potential of a mission like CORE for these analyses, synergies with other planned and ongoing projects are also discussed.
We consider a field theory model of coupled dark energy which treats dark energy as a three-form field and dark matter as a spinor field. By assuming the effective mass of dark matter as a power-law function of the three-form field and neglecting the potential term of dark energy, we obtain three solutions of the autonomous system of evolution equations, including a de Sitter attractor, a tracking solution and an approximate solution which shows that the effective EOS of dark energy can pass through $-1$ at a low redshift that depends on the coupling constant $\lambda$. To understand the strength of the coupling, we confront the model with the latest Type Ia Supernova (SN \uppercase\expandafter{\romannumeral1}a), Baryon Acoustic Oscillations (BAO) and Cosmic Microwave Backround (CMB) radiation observations, with the conclusion that the combination of these three databases marginalized over the present dark matter density parameter $\Omega_{m0}$ and the present three-form field $\kappa X_{0}$ gives stringent constraints on the coupling constant, $-0.017< \lambda <0.047$ ($2\sigma$ confidence level), by which we give out the model applicable parameter range.
We present the first search for dark matter-induced delayed coincidence signals in a dual-phase xenon time projection chamber, using the 224.6\,live days of the XENON100 science run~II. This very distinct signature is predicted in the framework of magnetic inelastic dark matter which has been proposed to reconcile the modulation signal reported by the DAMA/LIBRA collaboration with the null results from other direct detection experiments. No candidate event has been found in the region of interest and upper limits on the WIMP's magnetic dipole moment are derived. The scenarios proposed to explain the DAMA/LIBRA modulation signal by magnetic inelastic dark matter interactions of WIMPs with masses of 58.0\,GeV/c$^2$ and 122.7\,GeV/c$^2$ are excluded at 3.3\,$\sigma$ and 9.3\,$\sigma$, respectively.
We study the constraints imposed by the requirement of Asymptotic Safety on a class of inflationary models with an inflaton field non-minimally coupled to the Ricci scalar. The critical surface in the space of theories is determined by the improved renormalization group flow which takes into account quantum corrections beyond the one loop approximation. The combination of constraints deriving from Planck observations and those from theory puts severe bounds on the values of the parameters of the model and predicts a quite large tensor to scalar ratio. We finally comment on the dependence of the results on the definition of the infrared energy scale which parametrises the running on the critical surface.
The diffusive shock acceleration scenario is usually invoked to explain radio relics, although the detailed driving mechanism is still a matter of debate. Our aim is to constrain models for the origin of radio relics by comparing observed relic samples with simulated ones. Here we present a framework to homogeneously extract the whole sample of known radio relics from NVSS so that it can be used for comparison with cosmological simulations. In this way, we can better handle intrinsic biases in the analysis of the radio relic population. In addition, we show some properties of the resulting NVSS sample relics such as the correlation between relic shape and orientation with respect to the cluster. Also, we briefly discuss the typical relic surface brightness and its relation to projected cluster distance and relic angular sizes.
We present a toolbox of new techniques and concepts for the efficient forecasting of experimental sensitivities. These are applicable to a large range of scenarios in (astro-)particle physics, and based on the Fisher information formalism. Fisher information provides an answer to the question what is the maximum extractable information from a given observation?. It is a common tool for the forecasting of experimental sensitivities in many branches of science, but rarely used in astroparticle physics or searches for particle dark matter. After briefly reviewing the Fisher information matrix of general Poisson likelihoods, we propose very compact expressions for estimating expected exclusion and discovery limits (equivalent counts method). We demonstrate by comparison with Monte Carlo results that they remain surprisingly accurate even deep in the Poisson regime. We show how correlated background systematics can be efficiently accounted for by a treatment based on Gaussian random fields. Finally, we introduce the novel concept of Fisher information flux. It can be thought of as a generalization of the commonly used signal-to-noise ratio, while accounting for the non-local properties and saturation effects of background and instrumental uncertainties. It is a powerful and flexible tool ready to be used as core concept for informed strategy development in astroparticle physics and searches for particle dark matter.
By using the Gauss-Bonnet theorem, the bending angle of light in a static, spherically symmetric and asymptotically flat spacetime has been recently discussed, especially by taking account of the finite distance from a lens object to a light source and a receiver [Ishihara, Suzuki, Ono, Asada, Phys. Rev. D 95, 044017 (2017)]. We discuss a possible extension of the method of calculating the bending angle of light to stationary, axisymmetric and asymptotically flat spacetimes. For this purpose, we consider the light rays on the equatorial plane in the axisymmetric spacetime. We introduce a spatial metric to define the bending angle of light in the finite-distance situation. We show that the proposed bending angle of light is coordinate-invariant by using the Gauss-Bonnet theorem. The non-vanishing geodesic curvature of the photon orbit with the spatial metric is caused in gravitomagnetism, even though the light ray in the four-dimensional spacetime follows the null geodesic. Finally, we consider Kerr spacetime as an example in order to examine how the bending angle of light is computed by the present method. The finite-distance correction to the gravitomagnetic deflection angle due to the Sun's spin is around a pico-arcsecond level. The finite-distance corrections for Sgr A$^{\ast}$ also are estimated to be very small. Therefore, the gravitomagnetic finite-distance corrections for these objects are unlikely to be observed with present technology.
The cosmological particle horizon is the maximum measurable length in the Universe. The existence of such a maximum observable length scale implies a modification of the quantum uncertainty principle. Thus due to non-locality of quantum mechanics, the global properties of the Universe could produce a signature on the behaviour of local quantum systems. A Generalized Uncertainty Principle (GUP) that is consistent with the existence of such a maximum observable length scale $l_{max}$ is $\Delta x \Delta p \geq \frac{\hbar}{2}\;\frac{1}{1-\alpha \Delta x^2}$ where $\alpha = l_{max}^{-2}\simeq (H_0/c)^2$ ($H_0$ is the Hubble parameter and $c$ is the speed of light). In addition to the existence of a maximum measurable length $l_{max}=\frac{1}{\sqrt \alpha}$, this form of GUP implies also the existence of a minimum measurable momentum $p_{min}=\frac{3 \sqrt{3}}{4}\hbar \sqrt{\alpha}$. Using appropriate representation of the position and momentum quantum operators we show that the spectrum of the one dimensional harmonic oscillator becomes $\bar{\mathcal{E}}_n=2n+1+\lambda_n \bar{\alpha}$ where $\bar{\mathcal{E}}_n\equiv 2E_n/\hbar \omega$ is the dimensionless properly normalized $n^{th}$ energy level, $\bar{\alpha}$ is a dimensionless parameter with $\bar{\alpha}\equiv \alpha \hbar/m \omega$ and $\lambda_n\sim n^2$ for $n\gg 1$ (we show the full form of $\lambda_n$ in the text). For a typical vibrating diatomic molecule and $l_{max}=c/H_0$ we find $\bar{\alpha}\sim 10^{-77}$ and therefore for such a system, this effect is beyond reach of current experiments. However, this effect could be more important in the early universe and could produce signatures in the primordial perturbation spectrum induced by quantum fluctuations of the inflaton field.
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We present results from large-scale numerical simulations of a first order thermal phase transition in the early universe, in order to explore the shape of the acoustic gravitational wave and the velocity power spectra. We compare the results with the predictions of the recently proposed sound shell model. For the gravitational wave power spectrum, we find that the predicted $k^{-3}$ behaviour, where $k$ is the wavenumber, emerges clearly for detonations. The power spectra from deflagrations show similar features, but exhibit a steeper high-$k$ decay and an extra feature not accounted for in the model. There are two independent length scales: the mean bubble separation and the thickness of the sound shell around the expanding bubble of the low temperature phase. It is the sound shell thickness which sets the position of the peak of the power spectrum. The low wavenumber behaviour of the velocity power spectrum is consistent with a causal $k^{3}$, except for the thinnest sound shell, where it is steeper. We present parameters for a simple broken power law fit to the gravitational wave power spectrum for wall speeds well away from the speed of sound where this form can be usefully applied. We examine the prospects for the detection, showing that a LISA-like mission has the sensitivity to detect a gravitational wave signal from sound waves with an RMS fluid velocity of about $0.05c$, produced from bubbles with a mean separation of about $10^{-2}$ of the Hubble radius. The shape of the gravitational wave power spectrum depends on the bubble wall speed, and it may be possible to estimate the wall speed, and constrain other phase transition parameters, with an accurate measurement of a stochastic gravitational wave background.
Unresolved sources of gravitational waves are at the origin of a stochastic gravitational wave background. While the computation of its mean density as a function of frequency in a homogeneous and isotropic universe is standard lore, the computation of its anisotropies requires to understand the coarse graining from local systems, to galactic scales and then to cosmology. An expression of the gravitational wave energy density valid in any general spacetime is derived. It is then specialized to a perturbed Friedmann-Lema\^itre spacetime in order to determine the angular power spectrum of this stochastic background as well as its correlation with other cosmological probes, such as the galaxy number counts and weak lensing. Our result for the angular power spectrum also provides an expression for the variance of the gravitational wave background.
We present spectroscopic identification of 32 new quasars and luminous galaxies discovered at 5.7 < z < 6.8. This is the second in a series of papers presenting the results of the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multi-band imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The photometric candidates were selected by a Bayesian probabilistic algorithm, and then observed with spectrographs on the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous paper, we have now identified 64 HSC sources over about 430 deg2, which include 33 high-z quasars, 14 high-z luminous galaxies, 2 [O III] emitters at z ~ 0.8, and 15 Galactic brown dwarfs. The new quasars have considerably lower luminosity (M1450 ~ -25 to -22 mag) than most of the previously known high-z quasars. Several of these quasars have luminous (> 10^(43) erg/s) and narrow (< 500 km/s) Ly alpha lines, and also a possible mini broad absorption line system of N V 1240 in the composite spectrum, which clearly separate them from typical quasars. On the other hand, the high-z galaxies have extremely high luminosity (M1450 ~ -24 to -22 mag) compared to other galaxies found at similar redshift. With the discovery of these new classes of objects, we are opening up new parameter spaces in the high-z Universe. Further survey observations and follow-up studies of the identified objects, including the construction of the quasar luminosity function at z ~ 6, are ongoing.
We study the propagation of ultra-high-energy cosmic rays in the magnetised cosmic web. We focus on the particular case of highly magnetised voids ($B \sim \text{nG}$), using the upper bounds from the Planck satellite. The cosmic web was obtained from purely magnetohydrodynamical cosmological simulations of structure formation considering different power spectra for the seed magnetic field in order to account for theoretical uncertainties. We investigate the impact of these uncertainties on the propagation of cosmic rays, showing that they can affect the measured spectrum and composition by up to $\simeq 80\%$ and $\simeq 5\%$, respectivelly. In our scenarios, even if magnetic fields in voids are strong, deflections of 50 EeV protons from sources closer than $\sim\;$50 Mpc are less than $15^\circ$ in approximately 10-50% of the sky, depending on the distribution of sources and magnetic power spectrum. Therefore, UHECR astronomy might be possible in a significant portion of the sky depending on the primordial magnetic power spectrum, provided that protons constitute a sizeable fraction of the observed UHECR flux.
We propose the study of constant-roll inflation in $F(R)$ gravity. We use two different approaches, one that relates an $F(R)$ gravity to well known scalar models of constant-roll and a second that examines directly the constant-roll condition in $F(R)$ gravity. With regards to the first approach, by using well known techniques, we find the $F(R)$ gravity which realizes a given constant-roll evolution in the scalar-tensor theory. We also perform a conformal transformation in the resulting $F(R)$ gravity and we find the Einstein frame counterpart theory. As we demonstrate, the resulting scalar potential is different in comparison to the original scalar constant-roll case, and the same applies for the corresponding observational indices. Moreover, we discuss how cosmological evolutions that can realize constant-roll to constant-roll eras transitions in the scalar-tensor description, can be realized by vacuum $F(R)$ gravity. With regards to the second approach, we examine directly the effects of the constant-roll condition on the inflationary dynamics of vacuum $F(R)$ gravity. We present in detail the formalism of constant-roll $F(R)$ gravity inflationary dynamics and we discuss how the inflationary indices become in this case. We use two well known $F(R)$ gravities in order to illustrate our findings, the $R^2$ model and a power-law $F(R)$ gravity in vacuum. As we demonstrate, in both cases the parameter space is enlarged in comparison to the slow-roll counterparts of the models, and in effect, the models can also be compatible with the observational data. Finally, we briefly address the graceful exit issue.
We present initial results from the Subaru Strategic Program (SSP) with Hyper Suprime-Cam (HSC) on a comprehensive survey of emission line galaxies at $z<1.5$. In the first data release of the HSC-SSP, two narrowband data (NB816 and NB921) down to 25.6--25.9 mag at $5 \sigma$ are available over 17 deg$^2$, which allow us to construct unprecedentedly large samples of 18,792 H$\alpha$ emitters at $z \approx$ 0.25 and 0.40, 16,051 [OIII] emitters at $z \approx$ 0.63 and 0.84, and 28,157 [OII] emitters at $z \approx$ 1.19 and 1.47. We reveal the cosmic web on a scale of more than 50 comoving Mpc where some galaxy clusters identified by red sequence galaxies are located on the intersection of filamentary structures of star-forming galaxies. The luminosity functions for the emission line galaxies are consistent with the previous studies, except for the bright end of the luminosity functions for the H$\alpha$ emitters at $z \approx$ 0.25--0.40. This is likely due to small survey volumes probed by previous studies which is sensitive to the cosmic variance. The wide field coverage of the data allows us to overcome the cosmic variance and derive the bright end of the luminosity functions more precisely than the previous studies. We also investigate the stellar mass functions for the H$\alpha$ emitters at $z \approx$ 0.25--0.40 and find that they are consistent with those from the stellar mass limited samples. Thus, our samples of the emission line galaxies are the representative ones of star-forming galaxies at the redshifts probed.
We present the environmental dependence of colour, stellar mass, and star formation (SF) activity in H-alpha-selected galaxies along the huge cosmic web at z=0.4 hosting twin clusters in DEEP2-3 field, discovered by Subaru Strategic Programme of Hyper Suprime-Cam (HSC SSP). By combining photo-z selected galaxies and H-alpha emitters selected with broad-band and narrow-band data of the recent internal data release of HSC SSP (DR1), we confirm that galaxies in higher-density environments or galaxies in the cluster central regions show redder colours. We find that there still remains a colour-density and colour-radius correlation even if we restrict the sample to H-alpha-selected galaxies. We also find an increase of star formation rates (SFR), and possible decline in specific SFRs, amongst H-alpha emitters towards the highest-density environment, primarily driven by the excess of red/massive H-alpha emitters in high-density environment. Finally, we find a hint that pairs of H-alpha emitters located in higher-density environment show redder colours than those in underdense regions, implying that galaxy-galaxy interaction in different environments have different impacts on the properties of SF galaxies.
We study the stability of a recently proposed model of scalar-field matter called mimetic dark matter or imperfect dark matter. It has been known that mimetic matter with higher derivative terms suffers from gradient instabilities in scalar perturbations. To seek for an instability-free extension of imperfect dark matter, we develop an effective theory of cosmological perturbations subject to the constraint on the scalar field's kinetic term. This is done by using the unifying framework of general scalar-tensor theories based on the ADM formalism. We demonstrate that it is indeed possible to construct a model of imperfect dark matter which is free from ghost and gradient instabilities. As a side remark, we also show that mimetic $F({\cal R})$ theory is plagued with the Ostrogradsky instability.
Detection of the copious amount of X-ray emission from the dilute hot plasma in galaxy clusters suggests that a substantial fraction of the central intracluster medium (ICM) is cooling radiatively on a time scale much faster than the Hubble time. Theoretical models predict the cooling rate as high as about few hundred to few thousand solar mass per year, which would be then made available for the formation of new stars in the core of these clusters. However, systematic studies of the cores of such clusters failed to detect the expected reservoirs of cooled gas. Thus, the gas in the cores of galaxy clusters is losing substantial amount of energy in the form of X-rays but is not cooling. This in turn point towards the famous cooling flow paradox and hence demands some intermittent heating to balance the cooling over such a long period. Several sources have been suggested to counteract on the cooling of the ICM, however, the AGN feedback appeared to be the most promising and enough energetic source to resist cooling of the ICM in the cores of such clusters. In this presentation I will provide a brief overview on the feedback processes that are involved in the cores of the galaxy clusters with an emphasis on the AGN feedback and its observable signatures.
We investigate the galaxy overdensity around <2 pMpc-scale quasar pairs at high (z>3) and low (z~1) redshift based on the unprecedentedly wide and deep optical survey of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first-year survey data covering effectively ~121 deg2 in full-color and depth, we find two luminous pairs at z~3.6 and 3.3 which reside in $>5 \sigma$ overdense regions of g-dropout galaxies. The projected separations of the two pairs are $R_\perp=$1.75 and 1.04 pMpc, and their velocity offsets are $\Delta V=692$ and $1448$ km s$^{-1}$, respectively. This is in clear contrast to the average quasar environments in the same redshift range as discussed in Uchiyama et al. (2017), and implies that the quasar activity of the two pairs is triggered via major mergers in proto-clusters, unlike the vast majority of isolated quasars in general fields that may turn on due to non-merger events such as bar and disk instabilities. At z~1, we find 37 pairs in the current HSC-Wide coverage with $R_\perp<2$ pMpc and $\Delta V<2300$ km s$^{-1}$ including four from Hennawi et al. (2006). The distribution of the peak overdensity significance within two arcminutes around the pairs has a long tail toward high density ($>4\sigma$) regions. Thanks to the large sample size, we find a statistical evidence that this excess is unique in the pair environments when compared to single quasar and randomly-selected galaxy environments. Moreover, there are nine small-scale pairs with $R_\perp<1$ pMpc, two of which are found to reside in cluster fields. Our results demonstrate that quasar pairs at z~1-4 tend to occur in massive haloes, although perhaps not the most massive ones, and that they can be used to search for rare density peaks especially at high redshifts.
In this paper, we study thermodynamics of the cluster of galaxies under the effect of dynamical dark energy. We evaluate the configurational integral for interacting system of galaxies in an expanding universe by including the effects produced by the varying $\Lambda$. The gravitational partition function is obtained using this configuration integral. We obtain thermodynamics quantities in canonical ensemble which depend on time and investigate the second law of thermodynamics. We also calculate the distribution function in grand canonical ensemble. The time evolution of the clustering parameter of galaxies is investigated for the time dependent (dynamical) dark energy. We conclude that the second law of thermodynamics is valid for the total system of cluster of galaxies and dynamical dark energy. We calculate correlation function and show that our model is very close to Peebles's power law, in agreement with the N-body simulation. It is observed that thermodynamics quantities depend on the modified clustering parameter for this system of galaxies.
We study the formation of massive black holes in the first star clusters. We first locate star-forming gas clouds in proto-galactic halos of $\gtrsim10^7~M_{\odot}$ in cosmological hydrodynamics simulations and use them to generate the initial conditions for star clusters with masses of $\sim10^5~M_{\odot}$. We then perform a series of direct-tree hybrid $N$-body simulations to follow runaway stellar collisions in the dense star clusters. In all the cluster models except one, runaway collisions occur within a few million years, and the mass of the central, most massive star reaches $\sim400-1900~M_{\odot}$. Such very massive stars collapse to leave intermediate-mass black holes (IMBHs). The diversity of the final masses may be attributed to the differences in a few basic properties of the host halos such as mass, central gas velocity dispersion, and mean gas density of the central core. Finally, we derive the IMBH mass to cluster mass ratios, and compare them with the observed blackhole to bulge mass ratios in the present-day universe.
In the presence of massive bosonic degrees of freedom, rotational superradiance can trigger an instability that spins down black holes. This leads to peculiar gravitational-wave signatures and distribution in the spin-mass plane, which in turn can impose stringent constraints on ultralight fields. Here, we demonstrate that there is an analogous spindown effect for conducting stars. We show that rotating stars amplify low frequency electromagnetic waves, and that this effect is largest when the time scale for conduction within the star is of the order of a light crossing time. This has interesting consequences for dark photons, as massive dark photons would cause stars to spin down due to superradiant instabilities. The time scale of the spindown depends on the mass of the dark photon, and on the rotation rate, compactness, and conductivity of the star. Existing measurements of the spindown rate of pulsars place direct constraints on models of dark sectors. Our analysis suggests that dark photons of mass $m_V \sim 10^{-12}$ eV are excluded by pulsar-timing observations. These constraints also exclude superradiant instabilities triggered by dark photons as an explanation for the spin limit of observed pulsars.
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