Daniel Neves | Searcharxiv

arXiv2025

From scalar clouds around evaporating black holes to boson star

We study, for the first time, the evolution of a scalar cloud bound to an evaporating black hole. Our simulations of the associated Schr\"odinger-Poisson system for non-relativistic and spherically symmetric clouds reveal that a scalar cloud may (partially) survive as a self-gravitating boson star if the black hole evaporates adiabatically until its mass becomes less than one half of the cloud's mass. This yields a novel mechanism for boson star formation and shows that, as previously conjectured, bosonic dark matter production by light primordial black holes may result in micro-boson stars with very large occupation numbers, greatly enhancing their potential detectability even for very weakly interacting dark matter particles.

gr-qc↗

arXiv2024

Superradiant Darwinism: survival of the lightest axion

We study the dynamical evolution of superradiant instabilities of rotating black holes for multiple axion fields with comparable masses, motivated by string theory constructions, which typically exhibit a large number of light axions, with a broad range of masses. We show, in particular, that even though superradiant clouds for the heavier axion species grow faster, they are eventually reabsorbed by the black hole as the latter amplifies the lighter axion field(s), analogously to the dynamics of different species competing for the same resources in an ecosystem. We also incorporate in our study the effects of accretion and gravitational wave emission. We further demonstrate that the existence of multiple axion species with comparable masses may have a substantial impact on the stochastic gravitational wave background produced by axion clouds around black hole binary merger remnants, which could be probed with planned detectors.

hep-ph↗