Oscillon of Ultra-Light Axion-like Particle

TL;DR

This paper demonstrates through numerical simulation and analytical methods that ultra-light axion-like particles can form long-lived dense localized objects called oscillons, which may influence cosmological evolution.

Contribution

The study confirms oscillon formation in ULAP potentials and derives their lifetime analytically, highlighting their potential impact on cosmology.

Findings

Oscillons form in ULAP potentials as shown by simulations.

Long-lived oscillons can significantly affect cosmological evolution.

Analytical derivation of oscillon lifetime supports simulation results.

Abstract

Ultra-light axion-like particle (ULAP) is one of attractive candidates for cold dark matter. Because the de Broglie wavelength of ULAP with mass $\sim 10^{-22} {\rm eV}$ is $\mathcal{O}({\rm kpc})$, the suppression of the small scale structure by the uncertainty principle can solve the core-cusp problem. Frequently, ULAP is assumed to be uniformly distributed in the present universe. In typical ULAP potentials, however, strong self-resonance at the beginning of oscillation invokes the large fluctuations, which may cause the formation of the dense localized object, oscillon. % Such a dense object lives for a long time, it may affect the cosmological evolution. In this paper, we confirm the oscillon formation in a ULAP potential by numerical simulation and analytically derive its lifetime.