Stringy Effects During Inflation and Reheating

TL;DR

This paper explores how string theory effects during inflation and reheating in multi-throat compactifications could lead to observable cosmological signatures, including modifications to the CMB and a long string phase before standard reheating.

Contribution

It introduces a scenario where the compactification geometry changes during inflation, allowing for observable string effects without conflicting with the Hubble scale constraints.

Findings

Low string scale incompatible with high inflation Hubble scale

Modified compactification geometry during inflation is viable

Reheating may produce a long phase of open strings in the Standard Model sector

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.