Revisiting the cosmological coherent oscillation

TL;DR

This paper investigates how the coupling of scalar fields in the early Universe can suppress their abundance through a variant adiabatic mechanism, offering a solution to the cosmological saxion problem in supersymmetric models.

Contribution

It introduces a novel adiabatic suppression mechanism for scalar oscillations when coupled with another scalar field, reducing their cosmological impact.

Findings

The abundance of scalar fields can be significantly reduced.

The mechanism effectively solves the saxion cosmological problem.

Application to supersymmetric axion models demonstrates its viability.

Abstract

It is often the case that scalar fields are produced in the early Universe in the form of coherent oscillation. These scalar fields may have huge abundances and affect the evolution of the Universe. In particular, if the lifetime is long enough, they may cause cosmological disasters. We revisit the issue of coherent oscillation of the scalar field when it couples with another oscillating scalar field, and find a situation that the abundance, or the amplitude of the oscillation, is significantly reduced by a variant type of the adiabatic suppression mechanism. As a concrete example, it is applied to the saxion, a flat direction in the supersymmetric axion model, and we show that the cosmological saxion problem is solved in a particular setup.