On the Bondi accretion of a self-interacting complex scalar field

TL;DR

This paper investigates how a complex scalar field with a quartic potential accretes onto a black hole, revealing that deviations from perfect fluid behavior can be detected through accretion rates, which has implications for understanding fundamental fields in cosmology.

Contribution

It systematically analyzes relativistic Bondi accretion of a complex scalar field beyond the perfect fluid approximation, highlighting the impact of field properties on accretion rates.

Findings

Going beyond the perfect fluid approximation reduces accretion rates.

Black holes can distinguish between perfect fluids and their scalar field UV completions.

Scalar field accretion differs significantly from perfect fluid models.

Abstract

Scalar fields with a global U(1) symmetry often appear in cosmology and astrophysics. We study the spherically-symmetric, stationary accretion of such a classical field onto a Schwarzschild black hole in the test-field approximation. Thus, we consider the relativistic Bondi accretion beyond a simplified perfect-fluid setup. We focus on the complex scalar field with canonical kinetic term and with a generic quartic potential which either preserves the U(1) symmetry or exhibits spontaneous symmetry breaking. It is well known that in the lowest order in gradient expansion the dynamics of such a scalar field is well approximated by a perfect superfluid; we demonstrate that going beyond this approximation systematically reduces the accretion rate with respect to the perfect fluid case. Hence, black holes can provide a way to distinguish a perfect fluid from its ultraviolet completion in form of the complex scalar field.