Oscillons of Axion-Like Particle: Mass distribution and power spectrum

TL;DR

This paper studies oscillons formed by Axion-Like Particles in string theory, analyzing their distribution, stability, and impact on the universe using lattice simulations and decay rate models.

Contribution

It provides the first detailed analysis of oscillon properties for pure-natural type potentials, including their number density, mass distribution, and power spectrum.

Findings

Oscillons can survive for cosmological timescales, especially for ultra-light ALPs.

The mass distribution of oscillons peaks at specific values depending on the potential.

The energy ratio of oscillons to the ALP field influences cosmic evolution.

Abstract

In string theory, the simultaneous existence of many Axion-Like Particles (ALPs) are suggested over a vast mass range, and a variety of potentials have been developed in the context of inflation. In such potentials shallower than quadratic, the prominent instability can produce localized dense objects, oscillons. Because of the approximate conservation of their adiabatic invariant, oscillons generally survive quite long, maybe up to the current age of the universe in the case of ultra-light ALPs with $m \sim 10^{-22}\ {\rm eV}$. Such oscillons can have significant effects on the evolution of the recent universe. In this paper, we investigate the oscillons of the pure-natural type potential by classical lattice simulation to explore the key quantities necessary for phenomenological application: the number density of oscillons, the oscillon mass distribution, the energy ratio of oscillons to the ALP field, and the power spectrum. Then, we evolve these values in consideration of the analytic decay rate.