The Ultra Slow-Roll Phase Of Warm Inflation In Braneworld Cosmology

TL;DR

This paper investigates the Ultra Slow Roll phase of warm inflation within braneworld cosmologies, analyzing how brane effects influence inflationary dynamics and primordial perturbations, with a focus on Randall-Sundrum and DGP models.

Contribution

It introduces a detailed study of USR in warm inflation on braneworld backgrounds, highlighting the suppression of brane effects during USR phases.

Findings

Brane contributions diminish during USR, approaching standard inflation.

Numerical results show the evolution of the primordial power spectrum.

The study extends inflationary models to include braneworld effects in USR.

Abstract

Slow-roll of the inflaton (inflationary field) defines the standard dynamics of the inflationary epoch. However, the inflaton deviates from slow-roll when it encounters an extremely flat region in the inflationary potential, and enters a phase dubbed Ultra Slow Roll (USR). In previous studies, there have been various theories which modify the theory of general relativity, all of them having different motivations based on different paradigms. Among these, braneworld gravity, motivated from string theory; is one of the most prominent theories as it provides a geometrical explanation for the weakness of gravity. In this article, we explore two possible braneworld background theories, the Randall-Sundrum (RS-II) model and the Dvali-Gabadadze-Porratai (DGP) model, and then realize an USR phase in a particularly interesting inflationary scenario, called warm inflation. In the warm inflationary scenario, a thermal radiation bath coexists with the inflationary energy density as an effect of the dissipative dynamics. We then derive inflationary slow roll parameters and the primordial power spectrum of scalar curvature perturbations in such a setup. We then numerically investigate the evolution of the inflaton and the primordial power spectrum of scalar curvature perturbations. Our analysis shows that the braneworld contributions become progressively suppressed as the USR conditions are made more stringent, indicating that the USR phase effectively diminishes brane-induced corrections to standard inflationary dynamics.