Axion Miniclusters in Modified Cosmological Histories

TL;DR

This paper explores how different early-universe cosmological histories significantly affect the formation, properties, and potential detectability of axion miniclusters, offering insights into pre-Big Bang Nucleosynthesis conditions.

Contribution

It provides a detailed analysis of axion minicluster characteristics in various alternative cosmologies, highlighting their dependence on the universe's expansion history.

Findings

Minicluster mass and radius can vary by many orders of magnitude depending on cosmology.

Altered cosmological histories impact the detectability of axion miniclusters.

Results can inform future experimental searches and probe pre-Big Bang Nucleosynthesis universe.

Abstract

If the symmetry breaking leading to the origin of the axion dark matter field occurs after the end of inflation and is never restored, then overdensities in the axion field collapse to form dense objects known in the literature as axion miniclusters. The estimates of the typical minicluster mass and radius strongly depend on the details of the cosmology at which the onset of axion oscillations begin. In this work we study the properties and phenomenology of miniclusters in alternative cosmological histories and find that they can change by many orders of magnitude. Our findings have direct implications on current and future experimental searches and, in the case of discovery, could be used to learn something about the universe expansion prior to Big-Bang-Nucleosynthesis.