Moduli-Induced Axion Problem

TL;DR

The paper highlights that even heavy moduli fields can cause cosmological issues by decaying into axions, which are constrained by recent observations, challenging previous assumptions about resolving the moduli problem.

Contribution

It demonstrates that the cosmological moduli problem persists due to axion production and explores potential solutions in specific models, extending understanding beyond previous assumptions.

Findings

Heavy moduli decay into axions, affecting cosmology.

Axion abundance constraints are tighter than previously thought.

Potential solutions to the moduli-induced axion problem are discussed.

Abstract

We point out that the cosmological moduli problem is not necessarily resolved even if the modulus mass is heavier than O(10)TeV, contrary to the common wisdom. The point is that, in many scenarios where the lightest moduli fields are stabilized by supersymmetry breaking effects, those moduli fields tend to mainly decay into almost massless axions, whose abundance is tightly constrained by the recent Planck results. We study the moduli-induced axion problem in concrete examples, and discuss possible solutions. The problem and its solutions are widely applicable to decays of heavy scalar fields which dominate the energy density of the Universe, for instance, the reheating of the inflaton.