Bose-Einstein Condensate Cosmology within the Framework of QCD Axion

TL;DR

This paper explores Bose-Einstein Condensation of axions in the early universe, analyzing its dynamics and potential role in black hole formation within a string-inspired QCD axion model.

Contribution

It introduces a detailed analysis of BEC formation driven by gravity and self-interactions in a string-inspired axion framework, linking early universe condensates to supermassive black holes.

Findings

BEC generation rate around redshift 30 matches phenomenological estimates

Self-interactions are crucial for condensate instability despite small magnitude

Early BEC formation potentially influences supermassive black hole development

Abstract

Bose-Einstein Condensation (BEC) cosmology is analyzed in the framework of a string-inspired axion model. The dispersion relation of the axionic mode includes both gravitational and self-interaction terms, the latter being small in magnitude but crucial for inducing instability of the condensate. The generation rate of BEC around redshift $z\approx 30$ is primarily governed by gravity, consistent with a phenomenological value $\Gamma\approx 10^{-31}$ eV adopted in previous work and realizable for the QCD axion. The relation between this early BEC epoch and the later formation of supermassive black holes at $z\approx 5$ is also discussed.