arXiv subjects

Gaurav Goswami

Publications and source records attributed to Gaurav Goswami.

23 records · Page 2Linked to original sources

arXiv2015

Revisiting a pre-inflationary radiation era and its effect on the CMB power spectrum

We revisit the scenario where inflation is preceded by a radiation era by considering that the inflaton too could have been in thermal equilibrium early in the radiation era. Hence we take into account not only the effect of a pre-inflationary era on the inflaton mode functions but also that of a frozen thermal distribution of inflaton quanta. We initially discuss in detail the issues relevant to our scenario of a pre-inflationary radiation dominated era and then obtain the scalar power spectrum for this scenario. We find that the power spectrum is free from infrared divergences. We then use the WMAP and Planck data to determine the constraints on the inflaton comoving `temperature' and on the duration of inflation. We find that the best fit value of the duration of inflation is less than 1 e-folding more than what is required to solve cosmological problems, while only an upper bound on the inflaton temperature can be obtained.

astro-ph.CO↗

arXiv2014

Primordial power spectrum features and consequences

The present Cosmic Microwave Background (CMB) temperature and polarization anisotropy data is consistent with not only a power law scalar primordial power spectrum (PPS) with a small running but also with the scalar PPS having very sharp features. This has motivated inflationary models with such sharp features. Recently, even the possibility of having nulls in the power spectrum (at certain scales) has been considered. The existence of these nulls has been shown in linear perturbation theory. What shall be the effect of higher order corrections on such nulls? Inspired by this question, we attempt to calculate quantum radiative corrections to the Fourier transform of the two-point function in a toy field theory and address the issue of how these corrections to the power spectrum behave in models in which the tree-level power spectrum has a sharp dip (but not a null). In particular, we consider the possibility of the relative enhancement of radiative corrections in a model in which the tree-level spectrum goes through a dip in power at a certain scale. The mode functions of the field (whose power spectrum is to be evaluated) are chosen such that they undergo the kind of dynamics that leads to a sharp dip in the tree level power spectrum. Next we consider the situation in which this field has quartic self interactions and find one loop correction in a suitably chosen renormalization scheme. We thus attempt to answer the following key question in the context of this toy model (which is as important in the realistic case): in the chosen renormalization scheme, can quantum radiative corrections get enhanced relative to tree-level power spectrum at scales at which sharp dips appear in the tree-level spectrum?

astro-ph.CO↗

arXiv2014

On counterterms in cosmological perturbation theory

Cosmological perturbation theory is the theory of fluctuations (scalar as well as tensor) around the inflationary cosmological background solution. It is important to understand the details of the process of renormalization in this theory. In more familiar applications of quantum field theory, the dependence on the external momenta of the dimensionally regulated expression of the one-loop contribution to a correlator determines the number of counter terms (and their forms) required to renormalize it. In this work, it is pointed out that in cosmological perturbation theory, though this still happens, it happens in a completely different way such that in the late time limit, the information about the number and forms of counter terms required gets erased. This is to be compared with what happens in spontaneous symmetry breaking where the use of fluctuation fields around a chosen vacuum seems to suggest that more counter terms shall be needed to renormalize the theory than are actually required. We also comment on how the field strength of curvature perturbation, $ζ$, could get renormalized.

astro-ph.CO↗

arXiv2013

Maximum Entropy deconvolution of Primordial Power Spectrum

It is well known that CMB temperature anisotropies and polarization can be used to probe the metric perturbations in the early universe. Presently, there exist neither any observational detection of tensor modes of primordial metric perturbations nor of primordial non-Gaussianity. In such a scenario, primordial power spectrum of scalar metric perturbations is the only correlation function of metric perturbations (presumably generated during inflation) whose effects can be directly probed through various observations. To explore the possibility of any deviations from the simplest picture of the era of cosmic inflation in the early universe, it thus becomes extremely important to uncover the amplitude and shape of this (only available) correlation sufficiently well. In the present work, we attempt to reconstruct the primordial power spectrum of scalar metric perturbations using the binned (uncorrelated) CMB temperature anisotropies data using the Maximum Entropy Method (MEM) to solve the corresponding inverse problem. Our analysis shows that, given the current CMB data, there are no convincing reasons to believe that the primordial power spectrum of scalar metric perturbations has any significant features.

astro-ph.CO↗

arXiv2011

Power spectrum nulls due to non-standard inflationary evolution

The simplest models of inflation based on slow roll produce nearly scale invariant primordial power spectra (PPS). But there are also numerous models that predict radically broken scale invariant PPS. In particular, markedly cuspy dips in the PPS correspond to nulls where the perturbation amplitude, hence PPS, goes through a zero at a specific wavenumber. Near this wavenumber, the true quantum nature of the generation mechanism of the primordial fluctuations may be revealed. Naively these features may appear to arise from fine tuned initial conditions. However, we show that this behavior arises under fairly generic set of conditions involving super-Hubble scale evolution of perturbation modes during inflation. We illustrate this with the well-studied examples of punctuated inflation and the Starobinsky-break model.

astro-ph.CO↗