Reheating Closed String Inflation

TL;DR

The paper investigates how UV-protection mechanisms for the inflaton impact reheating in closed-string inflation, using N-flation as a concrete example. It shows that inflaton couplings tend to populate hidden sectors, making BBN and over-closure constraints stringent and often requiring tuning to favor the Standard Model. It provides quantitative analyses of relic abundances and an alignment-based tuning measure, and discusses generalizations to other closed-string setups and observational implications. The work suggests hidden-sector relics as a potentially generic UV-physics signature and highlights gravitational wave and dark-matter signatures as avenues for testing UV completions of inflation.

Abstract

Protecting the inflationary potential from quantum corrections typically requires symmetries that constrain the form of couplings of the inflaton to other sectors. We will explore how these restrictions affect reheating in models with UV completions. In particular, we look at how reheating occurs when inflation is governed by closed strings, using N-flation as an example. We find that coupling the inflaton preferentially to the Standard Model is difficult, and hidden sectors are typically reheated. Observational constraints are only met by a fraction of the models. In some working models, relativistic relics in the hidden sector provide dark matter candidates with masses that range from keV to PeV, with lighter masses being preferred.