We study the cosmological properties of a dynamical of dark energy (DE) component determined by a Steep Equation of State (SEoS) $w(z)=w_0+w_i\frac{(z/z_T)^q}{1+(z/z_T)^q}$. The SEoS has a transition at $z_T$ between two pivotal values ($w_i, w_0$) which can be taken as an early time and present day values of $w$ and the steepness is given by $q$. We describe the impact of this dynamical DE at background and perturbative level. The steepness of the transition has a better cosmological fit than a conventional CPL model with $w=w_0+w_a(1-a)$. Furthermore, we analyze the impact of steepness of the transition in the growth of matter perturbations and structure formation. This is manifest in the linear matter power spectrum, $P(k)$, the logarithmic growth function, $fσ_8(z)$, and the differential mass function $dn/d\log M(z=0)$. The differences in these last three quantities is at a percent-level using the same cosmological baseline parameters in our SEoS and a $ΛCDM$ model. However, we find an increase in the power spectrum, producing a bump at $k\approx k_T$ with $k_T\equiv a_TH(a_T)$ the mode associated to the time of the steep transition ($a_T = 1/(1+z_T)$). Different dynamics of DE lead to a different amount of DM at present time which has an impact in Power Spectrum and accordingly in structure formation.
We extensively study the evolution and distinct signatures of cosmological models, in which dark energy interacts directly with dark matter. We first focus on the imprints of these coupled models on the cosmic microwave background temperature power spectrum, in which we discuss the multipole peak separation together with the integrated Sachs-Wolfe effect. We also address the growth of matter perturbations, and disentangle the interacting dark energy models using the expansion history together with the growth history. We find that a disformal coupling between dark matter and dark energy induces…
In the present work, we study the large scale matter power spectrum as well as the observed galaxy power spectrum for non-canonical tachyon field dark energy model considering the full general relativistic perturbation equations. We form a set of coupled autonomous equations including both the background and linearly perturbed quantities and obtain their solutions numerically with proper set of initial conditions. We consider different scalar field potentials for our study. Deviations from concordance $Λ$CDM model are studied for different relevant quantities. Our study shows that non-canonica…
The 21 cm brightness temperature $δT_{\rm b}$ fluctuations from reionization promise to provide information on the physical processes during that epoch. We present a formalism for generating the $δT_{\rm b}$ distribution using dark matter simulations and an one-dimensional radiative transfer code. Our analysis is able to account for the spin temperature $T_{\rm S}$ fluctuations arising from inhomogeneous X-ray heating and Ly$α$ coupling during cosmic dawn. The $δT_{\rm b}$ power spectrum amplitude at large scales ($k \sim 0.1$ Mpc$^{-1}$) is maximum when $\sim 10\%$ of the gas (by volume) is h…
The redshifted 21 cm transition line of hydrogen tracks the thermal evolution of the neutral intergalactic medium (IGM) at "cosmic dawn," during the emergence of the first luminous astrophysical objects (~100 Myr after the Big Bang) but before these objects ionized the IGM (~400-800 Myr after the Big Bang). Because X-rays, in particular, are likely to be the chief energy courier for heating the IGM, measurements of the 21 cm signature can be used to infer knowledge about the first astrophysical X-ray sources. Using analytic arguments and a numerical population synthesis algorithm, we argue tha…
Dark Energy models with slowly-rolling cosmological scalar field provide a popular alternative to the standard, time-independent cosmological constant model. We study simultaneous evolution of background expansion and growth in the scalar field model with the Ratra-Peebles self-interaction potential. We use recent measurements of the linear growth rate and the baryon acoustic oscillation peak positions to constrain the model parameter $α$ that describes the steepness of the scalar field potential.
We consider the steepest rate at which the power spectrum from single field inflation can grow, with the aim of providing a simple explanation for the $k^4$ growth found recently. With this explanation in hand we show that a slightly steeper $k^5 (\log k )^2$ growth is in fact possible. Moreover, we argue that the power spectrum after a steep growth cannot immediately decay, but must remain large for the $k$ modes which exit during a $\sim2$ e-fold period. We also briefly consider how a strong growth can affect the spectral index of longer wavelengths preceding the growth, and show that even t…
We present a parametrization for the Dark Energy Equation of State "EoS" which has a rich structure, performing a transition at pivotal redshift $z_T$ between the present day value $w_0$ to an early time $w_i=w_a+w_0\equiv w(z\gg0)$ with a steepness given in terms of $q$ parameter. The proposed parametrization is $w=w_0+w_a(z/z_T)^q/(1+(z/z_T))^q$, with $w_0$, $w_i$, $q $ and $z_T$ constant parameters. It reduces to the widely used EoS $w=w_0+w_a(1-a)$ for $z_T=q=1$. This transition is motivated by scalar field dynamics such as for example quintessence models. We study if a late time transitio…
We study the nonlinear regime of large scale structure formation considering a dynamical dark energy (DE) component determined by a Steep Equation of State parametrization (SEoS) $w(z)=w_0+w_i\frac{(z/z_T)^q}{1+(z/z_T)^q}$. In order to perform the model exploration at low computational cost, we modified the public code L-PICOLA. We incorporate the DE model by means of the first and second-order matter perturbations in the Lagrangian frame and the expansion parameter. We analyze deviations of SEoS models with respect to $Λ$CDM in the non-linear matter power spectrum ($P_k$), the halo mass funct…
We derive analytic bounds on the shape of the primordial power spectrum in the context of single-field inflation. In particular, the steepest possible growth has a spectral index of $n_s - 1 = 4$ once transients have died down. Its primary implication is that any constraint on the power spectrum at a particular scale can be extrapolated to an upper bound over an extended range of scales. This is important for models which generate relics due to an enhanced amplitude of the primordial scalar perturbations, such as primordial black holes. In order to generate them, the power spectrum needs to gr…
The Standard Cosmological Model assumes that more than 85\% of matter is in the form of collisionless and pressureless dark matter. Unstable decaying dark matter has been proposed in the literature as an extension to the standard cold dark matter model. In this paper we investigate a scenario when dark matter decays and the resultant particle moves with respect to the dark matter. A covariant hydrodynamical model is developed in which the decay is modeled by the transfer of energy-momentum between two dark dust fluid components. We parameterise the model in terms of the decay rate $Γ$ and inje…
We investigate the characteristic modifications in the evolving cosmological perturbations when dark energy interacts with dust-like matter, causing the latter's background energy density fall off with time faster than usual. Focusing in particular to the late-time cosmic evolution, we show that such an interaction (of a specific form, arising naturally in a scalar-tensor formulation, or a wide range of modified gravity equivalents thereof), can have a rather significant effect on the perturbative spectrum, than on the background configuration which is not expected to get distorted much from $…
The early universe may have contained internally thermalized dark sectors that were decoupled from the Standard Model. In such scenarios, the relic dark thermal bath, composed of the lightest particle in the dark sector, can give rise to an epoch of early matter domination prior to Big Bang Nucleosynthesis, which has a potentially observable impact on the smallest dark matter structures. This lightest dark particle can easily and generically have number-changing self-interactions that give rise to "cannibal" behavior. We consider cosmologies where an initially sub-dominant cannibal species com…
We investigate the effects of warm dark matter (WDM) on the cosmic 21-cm signal. If dark matter exists as WDM instead of cold dark matter (CDM), its non-negligible velocities can inhibit the formation of low-mass halos that normally form first in CDM models, therefore delaying star-formation. The absence of early sources delays the build-up of UV and X-ray backgrounds that affect the 21-cm radiation signal produced by neutral hydrogen. With use of the 21CMFAST, code, we demonstrate that the pre-reionization 21-cm signal can be changed significantly in WDM models with a free-streaming length eq…
Global VLBI observations at 5 GHz have been performed to study the source morphology in 10 compact steep-spectrum (CSS) sources selected from the Peacock & Wall catalogue with the aim of finding asymmetric structures produced by the interaction with the ambient medium. The combination of these data and earlier 1.7-GHz observations allows the study of the spectral index distribution across the source structure and the unambiguous determination of the nature of each component. In seven sources we detected the core component with a flat or inverted spectrum. In six sources the radio emission has …
We present the first application of a "multiple-tracer" redshift-space distortion (RSD) analysis to an observational galaxy sample, using data from the Galaxy and Mass Assembly survey (GAMA). Our dataset is an r < 19.8 magnitude-limited sample of 178,579 galaxies covering redshift interval z < 0.5 and area 180 deg^2. We obtain improvements of 10-20% in measurements of the gravitational growth rate compared to a single-tracer analysis, deriving from the correlated sample variance imprinted in the distributions of the overlapping galaxy populations. We present new expressions for the covariances…
The free streaming motion of dark matter particles imprints a cutoff in the matter power spectrum and set the scale of the smallest dark matter halo. Recent cosmological $N$-body simulations have shown that the central density cusp is much steeper in haloes near the free streaming scale than in more massive haloes. Here, we study the abundance and structure of subhaloes near the free streaming scale at very high redshift using a suite of unprecedentedly large cosmological $N$-body simulations, over a wide range of the host halo mass. The subhalo abundance is suppressed strongly below the free …
Despite considerable experimental progress large parts of the axion-like particle (ALP) parameter space remain difficult to probe in terrestrial experiments. In some cases, however, small-scale structure of the ALP dark matter (DM) distribution is strongly enhanced, offering opportunities for astrophysical tests. Such an enhancement can be produced by a period of pre-nucleosynthesis early matter domination (EMD). This cosmology arises in many ultraviolet completions and generates the correct relic abundance for weak coupling $f_a\sim 10^{16}$ GeV, ALP masses in the range $10^{-13}$ eV $<m_a < …
The late-time integrated Sachs-Wolfe (ISW) imprint of $R\gtrsim 100~h^{-1}{\rm Mpc}$ super-structures is sourced by evolving large-scale potentials due to a dominant dark energy component in the $Λ$CDM model. The aspect that makes the ISW effect distinctly interesting is the repeated observation of stronger-than-expected imprints from supervoids at $z\lesssim0.9$. Here we analyze the un-probed key redshift range $0.8<z<2.2$ where the ISW signal is expected to fade in $Λ$CDM, due to a weakening dark energy component, and eventually become consistent with zero in the matter dominated epoch. On t…
Searches for modified gravity in the large-scale structure try to detect the enhanced amplitude of density fluctuations caused by the fifth force present in many of these theories. Neutrinos, on the other hand, suppress structure growth below their free-streaming length. Both effects take place on comparable scales, and uncertainty in the neutrino mass leads to a degeneracy with modified gravity parameters for probes that are measuring the amplitude of the matter power spectrum. We explore the possibility to break the degeneracy between modified gravity and neutrino effects in the growth of st…
If the inflaton couples to other degrees of freedom that populate the post-inflationary stage, such coupling modifies the dynamics of the inflaton \emph{during} inflation. We consider light fermions Yukawa coupled to the inflaton as "unobserved" degrees of freedom integrated out of the total density matrix. Tracing out these degrees of freedom yields a \emph{mixed} density matrix whose time evolution is described by an effective field theory. We show that the coupling leads to profuse fermion pair production for super-Hubble inflaton fluctuations which lead to the \emph{growth of entanglement …
Imprints of primordial magnetic fields in gravitational collapse during early structure formation
Carnegie Mellon University（卡内基梅隆大学）；Ilia State University（伊利亚国立大学）；Universit\'a di Bologna（博洛尼亚大学）；INAF Istituto di Radioastronomia（意大利国家天体物理研究所射电天文台）；Georgian National Astrophysical Observatory（格鲁吉亚国家天文台）
Motivated by the proposed time-delayed cosmology in the primordial inflationary era, we consider the application of the delayed Friedmann equation in the late-time Universe and explore some of its observable consequences. We study the background evolution predicted by the delayed Friedmann equation and determine the growth of Newtonian perturbations in this delayed background. We reveal smoking-gun imprints of time-delayed cosmology that can be traced to derivative discontinuities generic in delay differential equations. We show that a late-time cosmic delay is statistically consistent with Hu…
The universality of the halo mass function is investigated in the context of dark energy cosmologies. This widely used approximation assumes that the mass function can be expressed as a function of the matter density omega_m and the rms linear density fluctuation sigma only, with no explicit dependence on the properties of dark energy or redshift. In order to test this hypothesis we run a series of 15 high-resolution N-body simulations for different cosmological models. These consists of three LCDM cosmologies best fitting WMAP-1, 3 and 5 years data, and three toy-models characterized by a Rat…
We present resolved stellar photometry of 4 fields along the major axis of the M33 disk from images taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope. The photometry provides a detailed census of the red clump in all fields and reaches the ancient main sequence in the outermost field. Through detailed modeling of the color-magnitude diagrams, we find that the percentage of the stellar mass formed prior to z=1 changes from 71 +/- 9% in the innermost field to 16 +/- 6% in the outermost field. The disk shows a clear trend of increasing scale-length with time, evolving f…
