15,738 research outputs found
Universality of BSW mechanism for spinning particles
Ba\~nados (BSW) found that Kerr black holes can act as particle
accelerators with collisions at arbitrarily high center-of-mass energies.
Recently, collisions of particles with spin around some rotating black holes
have been discussed. In this paper, we study the BSW mechanism for spinning
particles by using a metric ansatz which describes a general rotating black
hole. We notice that there are two inequivalent definitions of center-of-mass
(CM) energy for spinning particles. We mainly discuss the CM energy defined in
terms of the worldline of the particle. We show that there exists an
energy-angular momentum relation that causes collisions with
arbitrarily high energy near-extremal black holes. We also provide a simple but
rigorous proof that the BSW mechanism breaks down for nonextremal black holes.
For the alternative definition of the CM energy, some authors find a new
critical spin relation that also causes the divergence of the CM mass. However,
by checking the timelike constraint, we show that particles with this critical
spin cannot reach the horizon of the black hole. Further numerical calculation
suggests that such particles cannot exist anywhere outside the horizon. Our
results are universal, independent of the underlying theories of gravity.Comment: 8 pages, 1 figure
Holographic complexity of the electromagnetic black hole
In this paper, we use the "complexity equals action" (CA) conjecture to
evaluate the holographic complexity in some multiple-horzion black holes for
F(Riemann) gravity coupled to a first-order source-free electrodynamics.
Motivated by the vanishing result of the purely magnetic black hole founded by
Goto , we investigate the complexity in a static charged black hole
with source-free electrodynamics and find that this vanishing feature of the
late-time rate is universal for a purely static magnetic black hole. However,
this result shows some unexpected features of the late-time growth rate. We
show how the inclusion of a boundary term for the first-order electromagnetic
field to the total action can make the holographic complexity be well-defined
and obtain a general expression of the late-time complexity growth rate with
these boundary terms. We apply our late-time result to some explicit cases and
show how to choose the proportional constant of these additional boundary terms
to make the complexity be well-defined in the zero-charge limit. For the static
magnetic black hole in Einstein gravity coupled to a first-order
electrodynamics, we find that there is a general relationship between the
proper proportional constant and the Lagrangian function h(\math{F}) of the
electromagnetic field: if h(\math{F}) is a convergent function, the choice of
the proportional constant is independent on explicit expressions of
h(\math{F}) and it should be chosen as ; if h(\math{F}) is a divergent
function, the proportional constant is dependent on the asymptotic index of the
Lagrangian function.Comment: 27 pages, 1 figure, some examples and references adde
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