Post-inflationary enhancement of adiabatic perturbations in modular cosmology

TL;DR

This paper demonstrates that in certain multi-field inflation models, entropic perturbations can be converted into adiabatic ones after inflation, leading to an enhanced curvature spectrum and implications for CMB observations.

Contribution

It introduces a mechanism where entropic perturbations influence adiabatic modes post-inflation in modular cosmology models, a novel insight in inflationary theory.

Findings

Curvature power spectrum is enhanced after inflation.

Entropic perturbations are converted into adiabatic perturbations post-inflation.

Implications for inflationary observables like $A_s$, $n_s$, and $r$.

Abstract

We show that multi-field inflationary models with negligible turning in field space during inflation can lead to an effective sourcing of adiabatic from entropic perturbations {\it after} the end of inflation. We illustrate this general phenomenon with a detailed analysis of an inflationary model whose scalar potential is determined by modular invariance. Its entropic perturbations are frozen during inflation, but instead, they are converted into adiabatic perturbations in the first post-inflationary $e$-folds. The curvature power spectrum, giving rise to CMB fluctuations, reaches a novel and enhanced plateau in this process; we address the implications for the inflationary observables $A_{s}$, $n_{s}$ and $r$.