Engineering topics

Aragam, Vikas

Publications and source records attributed to Aragam, Vikas.

3 records

DOE OSTI2024

${\tt Warm}$SPy: a numerical study of cosmological perturbations in warm inflation

We present ${\tt Warm}$SPy, a numerical code in Python designed to solve for the perturbations' equations in warm inflation models and compute the corresponding scalar power spectrum at CMB horizon crossing. In models of warm inflation, a radiation bath of temperature T during inflation induces a dissipation (friction) rate of strength Q ∝ T c /Φ m in the equation of motion for the inflaton field Φ. While for a temperature-independent dissipation rate (c = 0) an analytic expression for the scalar power spectrum exists, in the case of a non-zero value for c the set of equations can only be solved numerically. For c > 0 (c < 0), the coupling between the perturbations in the inflaton field and radiation induces a growing (decaying) mode in the scalar perturbations, generally parameterized by a multiplicative function G(Q) which we refer to as the scalar dissipation function. Using ${\tt Warm}$SPy, we provide an analytic fit for G(Q) for the cases of c = {3,1,-1}, corresponding to three cases that have been realized in physical models. Compared to previous literature results, our fits are more robust and valid over a broader range of dissipation strengths Q ϵ [10 -7 ,10 4 ]. Additionally, for the first time, we numerically assess the stability of the scalar dissipation function against various model parameters, inflationary histories as well as the effects of metric perturbations. As a whole, the results do not depend appreciably on most of the parameters in the analysis, except for the dissipation index c, providing evidence for the universal behaviour of the scalar dissipation function G(Q).

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Constraints on the scalar-field potential in warm inflation

In this work, we quantify the degree of fine-tuning required to achieve an observationally viable period of inflation in the strongly dissipative regime of warm inflation. The “fine-tuning” parameter λ is taken to be the ratio of the change in the height of the potential Δ V to the change in the scalar field (ΔΦ) 4 , i.e., the width of the potential, and therefore measures the requisite degree of flatness in the potential. The best motivated warm inflationary scenarios involve a dissipation rate of the kind Γ ∝ T c with c ≥ 0 , and for all such cases, the bounds on λ are tighter than those for standard cold inflation by at least 3 orders of magnitude. In other words, these models require an even flatter potential than standard inflation. On the other hand for the case of warm inflation with c < 0, we find that in a strongly dissipative regime the bound on λ can significantly weaken with respect to cold inflation. Thus, if a warm inflation model can be constructed in a strongly dissipative, negatively temperature-dependent regime, it accommodates steeper potentials otherwise ruled out in standard inflation.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Observational constraints on warm natural inflation

Warm natural inflation is studied for the case of the original cosine potential. The radiation bath during inflation induces a dissipation (friction) rate in the equation of motion for the inflation field, which can potentially reduce the field excursion needed for an observationally viable period of inflation. Here we examine if the dissipation thus provides a mechanism to avoid the large decay constant f ≳ M pl of cold cosine natural inflation. Whereas temperature independent dissipation has previously been shown to alleviate the need for a trans-Planckian decay constant f, we illustrate here the difficulties of accommodating a significantly sub-Planckian decay constant (f < 10 -1 M pl ) for the case of a temperature dependent dissipation rate in the form Γ ∝ T c , with c = {1,3}. Such dissipation rates represent physically well-motivated constructions in the literature. For each model, we map its location in the r-n s plane and compare with cosmic microwave background (CMB) data. For c = 1 (c = 3), we find that agreement with CMB data requires that dissipation be in the weak (moderate) regime and that the minimum allowed value of the decay constant in the potential is f min = 0.3 (0.8) M pl , respectively.

79 ASTRONOMY AND ASTROPHYSICS↗