Evolution Of Primordial Perturbations Research Articles

Modeling cosmological perturbations of thermal inflation

We consider a simple system consisting of matter, radiation and vacuum components to model the impact of thermal inflation on the evolution of primordial perturbations. The vacuum energy magnifies the primordial modes entering the horizon before its domination, making them potentially observable, and the resulting transfer function reflects the phase changes and energy contents. To determine the transfer function, we follow the curvature perturbation from well outside the horizon during radiation domination to well outside the horizon during vacuum domination and evaluate it on a constant radiation density hypersurface, as is appropriate for the case of thermal inflation. The shape of the transfer function is determined by the ratio of vacuum energy to radiation at matter-radiation equality, which we denote by , and has two characteristic scales, and , corresponding to the horizon sizes at matter radiation equality and the beginning of the inflation, respectively. If , the Universe experiences radiation, matter and vacuum domination eras and the transfer function is flat for , oscillates with amplitude for and oscillates with amplitude 1 for . For , the matter domination era disappears, and the transfer function reduces to being flat for and oscillating with amplitude 1 for .

Cosmology of a Chaplygin Gas Model Under f(T) Gravity and Evolution of Primordial Perturbations

This paper reports a detailed study of generalized Chaplygin gas (GCG) with power law form of scale factor and truncated form of the scale factor using binomial expansion in both interacting and non-interacting scenarios along with its cosmological consequences, studied in terms of equation of state (EoS) parameter. In the non-interacting scenario, the EoS parameter behaves as quintessence in both forms of the scale factor. In the interacting scenario, the EoS parameter behaves as phantom and for the truncated form of the scale factor, it violates the constraints of the positive parameter α. The cosmological implementation of GCG interacting with pressureless dark matter is investigated in the framework of f(T) modified gravity, where T is the torsion scalar in teleparallelism. The interaction term is directly proportional to the GCG density with positive coupling constant. In f(T) gravity, the EoS is behaving like phantom. The stability of the reconstructed model is investigated and it is found to be stable against small gravitational perturbations, i.e., the squared speed of sound is non-negative and an increasing function of cosmic time t. We have observed that our reconstructed f(T) model satisfies one of the sufficient conditions of a realistic reconstructed model and it is consistent with the CMB constraints and primordial nucleosynthesis. Cosmology of primordial perturbations has also been analyzed and the self-interacting potential has been found to be an increasing function of cosmic time t.

Scale-free power spectrums in the delayed cosmology

The delayed cosmology [JCAP 02(2012)046] assumes that the evolution of geometries is delayed relative to that of matter and/or energies. This idea allows inflation occur without inflaton fields or vacuum energies of any kind as drivings. We considered the production and evolution of primordial perturbations in this model. The results indicate that, with delaying, we could get a nearly scale-free power spectrum of perturbations starting from a radiation dominated early universe.

Galilean creation of the inflationary universe

It has been pointed out that the null energy condition can be violated stably in some non-canonical scalar-field theories. This allows us to consider the Galilean Genesis scenario in which the universe starts expanding from Minkowski spacetime and hence is free from the initial singularity. We use this scenario to study the early-time completion of inflation, pushing forward the recent idea of Pirtskhalava et al. We present a generic form of the Lagrangian governing the background and perturbation dynamics in the Genesis phase, the subsequent inflationary phase, and the graceful exit from inflation, as opposed to employing the effective field theory approach. Our Lagrangian belongs to a more general class of scalar-tensor theories than the Horndeski theory and Gleyzes-Langlois-Piazza-Vernizzi generalization, but still has the same number of the propagating degrees of freedom, and thus can avoid Ostrogradski instabilities. We investigate the generation and evolution of primordial perturbations in this scenario and show that one can indeed construct a stable model of inflation preceded by (generalized) Galilean Genesis.

STRUCTURE FORMATION IN DARK MATTER/DARK ENERGY DOMINATED UNIVERSES

In this work we present preliminary results of an analysis on the evolution of primordial baryonic and dark matter density perturbations. A top-hat hydrodynamic code has been utilized to analyze the evolution of these primordial perturbations, from the beginning of the recombination era until the redshift when the collapse occurs. All the relevant processes are included in the calculations, which includes the effect of a dark energy in the expanding universe. In particular, we find that the perturbations with dark matter collapse at very high redshift, which could explain the existence of old galaxies at high redshift. As a general result we find that the distribution of the non-baryonic dark matter is more concentrated than the baryonic one.

Evolution of primordial perturbations and a fluctuating decay rate

We present a gauge invariant formalism to study the evolution of curvature perturbations during decay of the inflaton or some other field that dominates the energy density. We specialize to the case where the total curvature perturbation arises predominantly from a spatially fluctuating decay rate. Gaussian fluctuations in the decay rate are present if the inflaton coupling or mass depends on some light field, which fluctuates freely during inflation. The isocurvature fluctuations of the light field seeds the total curvature perturbations, whose amplitude freezes after inflaton decay. We also analyze the resulting curvature perturbation starting with non-negligible values of the initial inflaton curvature. Lastly, we study the effects of the energy density stored in the light field.