Oscillons from String Moduli

TL;DR

This paper explores how string theory moduli can produce oscillons during cosmological evolution, potentially generating observable gravitational waves, and assesses the stability of these string vacua.

Contribution

It identifies conditions for oscillon formation in string cosmology and analyzes their phenomenology using explicit KKLT and LVS models.

Findings

Oscillons can form from displaced string moduli under certain conditions.

Produced oscillons may generate gravitational waves with frequencies near current observational ranges.

String vacua in KKLT and LVS are stable against local overshootings, ensuring their longevity.

Abstract

A generic feature of string compactifications is the presence of many scalar fields, called moduli. Moduli are usually displaced from their post-inflationary minimum during inflation. Their relaxation to the minimum could lead to the production of oscillons: localised, long-lived, non-linear excitations of the scalar fields. Here we discuss under which conditions oscillons can be produced in string cosmology and illustrate their production and potential phenomenology with two explicit examples: the case of an initially displaced volume modulus in the KKLT scenario and the case of a displaced blow-up Kaehler modulus in the Large Volume Scenario (LVS). One, in principle, observable consequence of oscillon dynamics is the production of gravitational waves which, contrary to those produced from preheating after high scale inflation, could have lower frequencies, closer to the currently observable range. We also show that, for the considered parameter ranges, oscillating fibre and volume moduli do not develop any significant non-perturbative dynamics. Furthermore, we find that the vacua in the LVS and the KKLT scenario are stable against local overshootings of the field into the decompatification region, which provides an additional check on the longevity of these metastable configurations.