3 research outputs found
Constraining the mass of dark photons and axion-like particles through black-hole superradiance
Ultralight bosons and axion-like particles appear naturally in different
scenarios and could solve some long-standing puzzles. Their detection is
challenging, and all direct methods hinge on unknown couplings to the Standard
Model of particle physics. However, the universal coupling to gravity provides
model-independent signatures for these fields. We explore here the superradiant
instability of spinning black holes triggered in the presence of such fields.
The instability taps angular momentum from and limits the maximum spin of
astrophysical black holes. We compute, for the first time, the spectrum of the
most unstable modes of a massive vector (Proca) field for generic black-hole
spin and Proca mass. The observed stability of the inner disk of stellar-mass
black holes can be used to derive \emph{direct} constraints on the mass of dark
photons in the mass range . By including also higher azimuthal modes, similar
constraints apply to axion-like particles in the mass range
.
Likewise, mass and spin distributions of supermassive BHs --~as measured
through continuum fitting, K iron line, or with the future space-based
gravitational-wave detector LISA~-- imply indirect bounds in the mass range
approximately , for both axion-like particles and dark photons. Overall,
superradiance allows to explore a region of approximately orders of
magnitude in the mass of ultralight bosons
Gravitational waves from scalar field accretion
Our aim in this work is to outline some physical consequences of the interaction between black holes and scalar field halos in terms of gravitational waves. In doing so, the black hole is taken as a static and spherically symmetric gravitational source, i.e. the Schwarzschild black hole, and we work within the test field approximation, considering that the scalar field lives in the curved space-time outside the black hole. We focused on the emission of gravitational waves when the black hole is perturbed by the surrounding scalar field matter. The symmetries of the space-time and the simplicity of the matter source allow, by means of a spherical harmonic decomposition, to study the problem by means of a one-dimensional description. Some properties of such gravitational waves are discussed as a function of the parameters of the infalling scalar field, and allow us to make the conjecture that the gravitational waves carry information on the type of matter that generated them. © 2011 American Physical Society