Cosmological Moduli and Non-perturbative Production of Axions

TL;DR

This paper explores how cosmological moduli influence early universe dynamics, particularly their role in enhancing axion production through decay processes, affecting dark matter and dark radiation scenarios.

Contribution

It provides a detailed analysis of moduli-axion interactions, including non-perturbative effects and their implications for cosmology within a comprehensive theoretical framework.

Findings

Enhanced axion production from modulus decay due to resonances

Implications for the cosmological moduli problem and dark radiation

Constraints on axion dark matter parameter space

Abstract

Cosmological moduli generically come to dominate the energy density of the early universe, and thereby trigger an early matter dominated era. Such non-standard cosmological histories are expected to have profound effects on the evolution and production of axion cold dark matter and dark radiation, as well as their prospects for detection. We consider moduli-axion couplings and investigate the early history of the coupled system, considering closely the evolution of the homogeneous modulus field, the back-reaction from the axion, and the energy densities of the two fields. A particular point of interest is the enhancement of axion production from modulus decay, due to tachyonic and parametric resonant instabilities, and the implications of such production on the cosmological moduli problem, axion dark radiation, and the available parameter space for axion dark matter. Using an effective field theory approach, WKB-based semi-analytical analysis, and detailed numerical estimates of the co-evolution of the system, we evaluate the expected decay efficiency of the modulus to axions. The effects of higher-order operators are studied and implications for UV-complete frameworks such as the Large Volume Scenarios in Type IIB string theory are considered in detail.