Superradiance — the 2020 Edition. (arXiv:1501.06570v7 [gr-qc] UPDATED)
<a href="http://arxiv.org/find/gr-qc/1/au:+Brito_R/0/1/0/all/0/1">Richard Brito</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Cardoso_V/0/1/0/all/0/1">Vitor Cardoso</a>, <a href="http://arxiv.org/find/gr-qc/1/au:+Pani_P/0/1/0/all/0/1">Paolo Pani</a>

Superradiance is a radiation enhancement process that involves dissipative
systems. With a 60 year-old history, superradiance has played a prominent role
in optics, quantum mechanics and especially in relativity and astrophysics. In
General Relativity, black-hole superradiance is permitted by the ergoregion,
that allows for energy, charge and angular momentum extraction from the vacuum,
even at the classical level. Stability of the spacetime is enforced by the
event horizon, where negative energy-states are dumped. Black-hole
superradiance is intimately connected to the black-hole area theorem, Penrose
process, tidal forces, and even Hawking radiation, which can be interpreted as
a quantum version of black-hole superradiance. Various mechanisms (as diverse
as massive fields, magnetic fields, anti-de Sitter boundaries, nonlinear
interactions, etc…) can confine the amplified radiation and give rise to
strong instabilities. These “black-hole bombs” have applications in searches of
dark matter and of physics beyond the Standard Model, are associated to the
threshold of formation of new black hole solutions that evade the no-hair
theorems, can be studied in the laboratory by devising analog models of
gravity, and might even provide a holographic description of spontaneous
symmetry breaking and superfluidity through the gauge-gravity duality.

This work is meant to provide a unified picture of this multifaceted subject.
We focus on the recent developments in the field, and work out a number of
novel examples and applications, ranging from fundamental physics to
astrophysics.

Superradiance is a radiation enhancement process that involves dissipative
systems. With a 60 year-old history, superradiance has played a prominent role
in optics, quantum mechanics and especially in relativity and astrophysics. In
General Relativity, black-hole superradiance is permitted by the ergoregion,
that allows for energy, charge and angular momentum extraction from the vacuum,
even at the classical level. Stability of the spacetime is enforced by the
event horizon, where negative energy-states are dumped. Black-hole
superradiance is intimately connected to the black-hole area theorem, Penrose
process, tidal forces, and even Hawking radiation, which can be interpreted as
a quantum version of black-hole superradiance. Various mechanisms (as diverse
as massive fields, magnetic fields, anti-de Sitter boundaries, nonlinear
interactions, etc…) can confine the amplified radiation and give rise to
strong instabilities. These “black-hole bombs” have applications in searches of
dark matter and of physics beyond the Standard Model, are associated to the
threshold of formation of new black hole solutions that evade the no-hair
theorems, can be studied in the laboratory by devising analog models of
gravity, and might even provide a holographic description of spontaneous
symmetry breaking and superfluidity through the gauge-gravity duality.

This work is meant to provide a unified picture of this multifaceted subject.
We focus on the recent developments in the field, and work out a number of
novel examples and applications, ranging from fundamental physics to
astrophysics.

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