Lyα forest power spectrum as an emerging window into the epoch of reionization and cosmic dawn

Conventional wisdom was that thermal relics from the epoch of reionization (EOR) would vanish swiftly. Recently, however, it was shown that these relics can survive to lower redshifts (z ∼ 2) than previously thought, due to gas at mean density being heated to T ∼ 3 × 104 K by reionization, which is inhomogeneous, and shocks. Given the high sensitivities of upcoming Lyα forest surveys, this effect will be a novel broadband systematic for cosmological application. From the astrophysical point of view, however, the imprint of inhomogeneous reionization can shed light on the EOR and cosmic dawn. We utilize a hybrid method — which includes two different simulation codes capable of handling the huge dynamical range — to show the impact of patchy reionization on the Lyα forest and its dependence on different astrophysical scenarios. We found statistically significant deviations in the 1D Lyα power spectrum at k = 0.14 cMpc−1 that range from $\sim 1\%$ at z = 2 up to almost $\sim 20\%$ at z = 4. The deviations in the 3D Lyα power spectrum, at the same wavenumber, are large and range from a few per cent at z = 2 up to $\sim 50\%$ at z = 4, although these deviations ignore the effect of He ii reionization and AGN feedback at z < 4. By exploiting different k-dependence of power spectrum among various astrophysical scenarios, the effect of patchy reionization on the Lyα forest power spectrum can open a new window into cosmic reionization and possibly cosmic dawn.

Assessing the effect of lens mass model in cosmological application with updated galaxy-scale strong gravitational lensing sample

ABSTRACT By comparing the dynamical and lensing masses of early-type lens galaxies, one can constrain both the cosmological parameters and the density profiles of galaxies. We explore the constraining power on cosmological parameters and the effect of the lens mass model in this method with 161 galaxy-scale strong lensing systems, which is currently the largest sample with both high-resolution imaging and stellar dynamical data. We assume a power-law mass model for the lenses, and consider three different parametrizations for γ (i.e. the slope of the total mass density profile) to include the effect of the dependence of γ on redshift and surface mass density. When treating δ (i.e. the slope of the luminosity density profile) as a universal parameter for all lens galaxies, we find the limits on the cosmological parameter Ωm are quite weak and biased, and also heavily dependent on the lens mass model in the scenarios of parametrizing γ with three different forms. When treating δ as an observable for each lens, the unbiased estimate of Ωm can be obtained only in the scenario of including the dependence of γ on both the redshift and the surface mass density, that is $\Omega _\mathrm{ m} = 0.381^{+0.185}_{-0.154}$ at 68 per cent confidence level in the framework of a flat ΛCDM model. We conclude that the significant dependencies of γ on both the redshift and the surface mass density, as well as the intrinsic scatter of δ among the lenses, need to be properly taken into account in this method.

Cosmology from multimeasure multifield model

We consider the cosmological application of a (variant of) relatively newly proposed model1 unifying inflation, dark energy, dark matter, and the Higgs mechanism. The model was originally defined using additional non-Riemannian measures, but it can be reformulated into effective quintessential model unifying inflation, dark energy and dark matter. Here, we demonstrate numerically that it is capable of describing the entire evolution of the Universe in a seamless way, but this requires some revision of the model setup. The main reason is that there is a strong effective friction in the model, a feature which has been neglected in the pioneer work. This improves the model potential for proper description of the evolution of the Universe, because the friction ensures a finite time inflation with dynamically maintained low-value slow-roll parameters in the realistic scenarios. In addition, the model predicts the existence of a constant scalar field in late Universe.

QCD at finite isospin chemical potential

We investigate the properties of QCD at finite isospin chemical potential at zero and non-zero temperatures. This theory is not affected by the sign problem and can be simulated using Monte-Carlo techniques. With increasing isospin chemical potential and temperatures below the deconfinement transition the system changes into a phase where charged pions condense, accompanied by an accumulation of low modes of the Dirac operator. The simulations are enabled by the introduction of a pionic source into the action, acting as an infrared regulator for the theory, and physical results are obtained by removing the regulator via an extrapolation. We present an update of our study concerning the associated phase diagram using 2+1 flavours of staggered fermions with physical quark masses and the comparison to Taylor expansion. We also present first results for our determination of the equation of state at finite isospin chemical potential and give an example for a cosmological application. The results can also be used to gain information about QCD at small baryon chemical potentials using reweighting with respect to the pionic source parameter and the chemical potential and we present first steps in this direction.

The effective Tolman temperature in curved spacetimes

We review a recently proposed effective Tolman temperature and present its applications to various gravitational systems. In the Unruh state for the evaporating black holes, the free-fall energy density is found to be negative divergent at the horizon, which is in contrast to the conventional calculations performed in the Kruskal coordinates. We resolve this conflict by invoking that the Kruskal coordinates could be no longer proper coordinates at the horizon. In the Hartle–Hawking–Israel state, despite the negative finite proper energy density at the horizon, the Tolman temperature is divergent there due to the infinite blueshift of the Hawking temperature. However, a consistent Stefan–Boltzmann law with the Hawking radiation shows that the effective Tolman temperature is eventually finite everywhere and the equivalence principle is surprisingly restored at the horizon. Then, we also show that the firewall necessarily emerges out of the Unruh vacuum, so that the Tolman temperature in the evaporating black hole is naturally divergent due to the infinitely blueshifted negative ingoing flux crossing the horizon, whereas the outgoing Hawking radiation characterized by the effective Tolman temperature indeed originates from the quantum atmosphere, not just at the horizon. So, the firewall and the atmosphere for the Hawking radiation turn out to be compatible, once we discard the fact that the Hawking radiation in the Unruh state originates from the infinitely blueshifted outgoing excitations at the horizon. Finally, as a cosmological application, the initial radiation energy density in warm inflation scenarios has been assumed to be finite when inflation starts. We successfully find the origin of the nonvanishing initial radiation energy density in the warm inflation by using the effective Tolman temperature.

Interacting modified Chaplygin gas in f(T) gravity framework and analysis of its stability against gravitational perturbation

In this work, we investigate the cosmological application of modified Chaplygin gas (MCG) interacting with pressureless dark matter (DM) in the [Formula: see text] modified gravity framework, where [Formula: see text] is the torsion scalar in teleparallelism. The interaction term has been chosen proportional to the MCG density with positive coupling constant. In the Einstein general relativity (GR) framework, the interacting MCG has been found to have equation of state (EoS) parameter behaving like quintessence. However, the [Formula: see text] gravity reconstructed via the interacting MCG has been found to have EoS crossing the phantom boundary of [Formula: see text]. Thus, one can generate a quintom-like EoS from an interacting MCG model in flat universe in the modified gravity cosmology framework. The reconstructed [Formula: see text] model has been found to interpolate between dust and [Formula: see text]CDM. Stability of the reconstructed [Formula: see text] has been investigated and it has been observed that the model is stable against gravitational perturbation. Cosmological evolution of primordial perturbations has also been investigated and the self-interacting potential has been found to increase with cosmic time and the squared speed of sound has been found to be non-negative.

Power-law entropy-corrected new holographic dark energy in Brans–Dicke cosmology

The purpose of this paper is to study power-law entropy-corrected holographic dark energy (PLECHDE) in the framework of Brans–Dicke cosmology with Granda–Oliveros (G-O) IR-cutoff. Considering the interacting and non-interacting scenario of PLECHDE with dark matter, we investigate the cosmological implications of this model in detail. We obtain the equation of state parameter, deceleration parameter, and evolution of dark energy density to explain expansion of the universe. We also determine these parameters for Ricci scale. We extend our study of the power-law entropy-corrected agegraphic dark energy model and calculate some cosmological parameters. Further, we show that the results that we calculate have good compatibility with previous work and matches it in the limiting case. Finally, we find a cosmological application of our work by evaluating the equation of state of dark energy for low red-shift.