Stringy Effects During Inflation and Reheating

TL;DR

This work argues that warped compactifications with multiple throats can elevate string and KK scales to near the Hubble scale during inflation, enabling potentially observable corrections to the CMB. It develops a self-consistent picture in which the SM throat is dynamically lifted during inflation, preserving EFT validity while allowing detectable stringy effects, and analyzes reheating via throat tunnelling, modulus dynamics, and a post-inflation long open-string phase. The authors quantify reheating channels, derive rates, and discuss cosmological consequences such as nonstandard expansion, isocurvature perturbations, primordial black holes, and gravitational waves. Overall, the paper identifies concrete signatures of string theory in early-universe cosmology and outlines a framework for connecting high-energy string dynamics to observable cosmological phenomena.

Abstract

We consider inflationary cosmology in the context of string compactifications with multiple throats. In scenarios where the warping differs significantly between throats, string and Kaluza-Klein physics can generate potentially observable corrections to the cosmology of inflation and reheating. First we demonstrate that a very low string scale in the ground state compactification is incompatible with a high Hubble scale during inflation, and we propose that the compactification geometry is altered during inflation. In this configuration, the lowest scale is just above the Hubble scale, which is compatible with effective field theory but still leads to potentially observable CMB corrections. Also in the appropriate region of parameter space, we find that reheating leads to a phase of long open strings in the Standard Model sector (before the usual radiation-dominated phase). We sketch the cosmology of the long string phase and we discuss possible observational consequences.