75 research outputs found
Pair of accelerated black holes in a de Sitter background: the dS C-metric
Following the work of Kinnersley and Walker for flat spacetimes, we have
analyzed the anti-de Sitter C-metric in a previous paper. In the de Sitter
case, Podolsky and Griffiths have established that the de Sitter C-metric (dS
C-metric) found by Plebanski and Demianski describes a pair of accelerated
black holes in the dS background with the acceleration being provided (in
addition to the cosmological constant) by a strut that pushes away the two
black holes or, alternatively, by a string that pulls them. We extend their
analysis mainly in four directions. First, we draw the Carter-Penrose diagrams
of the massless uncharged dS C-metric, of the massive uncharged dS C-metric and
of the massive charged dS C-metric. These diagrams allow us to clearly identify
the presence of two dS black holes and to conclude that they cannot interact
gravitationally. Second, we revisit the embedding of the dS C-metric in the 5D
Minkowski spacetime and we represent the motion of the dS C-metric origin in
the dS 4-hyperboloid as well as the localization of the strut. Third, we
comment on the physical properties of the strut that connects the two black
holes. Finally, we find the range of parameters that correspond to non-extreme
black holes, extreme black holes, and naked particles.Comment: 11 pages, 11 figures (RevTeX4). Published version: references adde
Duality between Electric and Magnetic Black Holes
A number of attempts have recently been made to extend the conjectured
duality of Yang Mills theory to gravity. Central to these speculations has been
the belief that electrically and magnetically charged black holes, the solitons
of quantum gravity, have identical quantum properties. This is not obvious,
because although duality is a symmetry of the classical equations of motion, it
changes the sign of the Maxwell action. Nevertheless, we show that the chemical
potential and charge projection that one has to introduce for electric but not
magnetic black holes exactly compensate for the difference in action in the
semi-classical approximation. In particular, we show that the pair production
of electric black holes is not a runaway process, as one might think if one
just went by the action of the relevant instanton. We also comment on the
definition of the entropy in cosmological situations, and show that we need to
be more careful when defining the entropy than we are in an asymptotically-flat
case.Comment: 23 pages, revtex, no figures. Major revision: two sections on the
electric Ernst solution adde
Two-phonon scattering of magnetorotons in fractional quantum Hall liquids
We study the phonon-assisted process of dissociation of a magnetoroton, in a
fractional quantum Hall liquid, into an unbound pair of quasiparticles. Whilst
the dissociation is forbidden to first order in the electron-phonon
interaction, it can occur as a two-phonon process. Depending on the value of
final separation between the quasiparticles, the dissociation is either a
single event involving absorption of one phonon and emission of another phonon
of similar energy, or a two-phonon diffusion of a quasiexciton in momentum
space. The dependence of the magnetoroton dissociation time on the filling
factor of the incompressible liquid is found.Comment: 4 pages, no figure
The extremal limits of the C-metric: Nariai, Bertotti-Robinson and anti-Nariai C-metrics
In two previous papers we have analyzed the C-metric in a background with a
cosmological constant, namely the de Sitter (dS) C-metric, and the anti-de
Sitter (AdS) C-metric, following the work of Kinnersley and Walker for the flat
C-metric. These exact solutions describe a pair of accelerated black holes in
the flat or cosmological constant background, with the acceleration A being
provided by a strut in-between that pushes away the two black holes. In this
paper we analyze the extremal limits of the C-metric in a background with
generic cosmological constant. We follow a procedure first introduced by
Ginsparg and Perry in which the Nariai solution, a spacetime which is the
direct topological product of the 2-dimensional dS and a 2-sphere, is generated
from the four-dimensional dS-Schwarzschild solution by taking an appropriate
limit, where the black hole event horizon approaches the cosmological horizon.
Similarly, one can generate the Bertotti-Robinson metric from the
Reissner-Nordstrom metric by taking the limit of the Cauchy horizon going into
the event horizon of the black hole, as well as the anti-Nariai by taking an
appropriate solution and limit. Using these methods we generate the C-metric
counterparts of the Nariai, Bertotti-Robinson and anti-Nariai solutions, among
others. One expects that the solutions found in this paper are unstable and
decay into a slightly non-extreme black hole pair accelerated by a strut or by
strings. Moreover, the Euclidean version of these solutions mediate the quantum
process of black hole pair creation, that accompanies the decay of the dS and
AdS spaces
Physics in the Real Universe: Time and Spacetime
The Block Universe idea, representing spacetime as a fixed whole, suggests
the flow of time is an illusion: the entire universe just is, with no special
meaning attached to the present time. This view is however based on
time-reversible microphysical laws and does not represent macro-physical
behaviour and the development of emergent complex systems, including life,
which do indeed exist in the real universe. When these are taken into account,
the unchanging block universe view of spacetime is best replaced by an evolving
block universe which extends as time evolves, with the potential of the future
continually becoming the certainty of the past. However this time evolution is
not related to any preferred surfaces in spacetime; rather it is associated
with the evolution of proper time along families of world linesComment: 28 pages, including 9 Figures. Major revision in response to referee
comment
Pair creation of anti-de Sitter black holes on a cosmic string background
We analyze the quantum process in which a cosmic string breaks in an anti-de
Sitter (AdS) background, and a pair of charged or neutral black holes is
produced at the ends of the strings. The energy to materialize and accelerate
the pair comes from the strings tension. In an AdS background this is the only
study done in the process of production of a pair of correlated black holes
with spherical topology. The acceleration of the produced black holes is
necessarily greater than (|L|/3)^(1/2), where L<0 is the cosmological constant.
Only in this case the virtual pair of black holes can overcome the attractive
background AdS potential well and become real. The instantons that describe
this process are constructed through the analytical continuation of the AdS
C-metric. Then, we explicitly compute the pair creation rate of the process,
and we verify that (as occurs with pair creation in other backgrounds) the pair
production of nonextreme black holes is enhanced relative to the pair creation
of extreme black holes by a factor of exp(Area/4), where Area is the black hole
horizon area. We also conclude that the general behavior of the pair creation
rate with the mass and acceleration of the black holes is similar in the AdS,
flat and de Sitter cases, and our AdS results reduce to the ones of the flat
case when L=0.Comment: 13 pages, 3 figures, ReVTeX
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