264 research outputs found
Boulware state and semiclassical thermodynamics of black holes in a cavity
A black hole, surrounded by a reflecting shell, acts as an effective
star-like object with respect to the outer region that leads to vacuum
polarization outside, where the quantum fields are in the Boulware state. We
find the quantum correction to the Hawking temperature, taking into account
this circumstance. It is proportional to the integral of the trace of the total
quantum stress-energy tensor over the whole space from the horizon to infinity.
For the shell, sufficiently close to the horizon, the leading term comes from
the boundary contribution of the Boulware state.Comment: 7 pages. To appear in Phys. Rev.
Dilaton black holes in grand canonical ensemble near the extreme state
Dilaton black holes with a pure electric charge are considered in a framework
of a grand canonical ensemble near the extreme state. It is shown that there
exists such a subset of boundary data that the Hawking temperature smoothly
goes to zero to an infinite value of a horizon radius but the horizon area and
entropy are finite and differ from zero. In string theory the existence of a
horizon in the extreme limit is due to the finiteness of a system only.Comment: 8 pages, RevTex 3.0. Presentation improved, discussion on metrics in
string theory simplified. To be published in Phys.Rev.
Two-dimensional quantum-corrected black hole in a finite size cavity
We consider the gravitation-dilaton theory (not necessarily exactly
solvable), whose potentials represent a generic linear combination of an
exponential and linear functions of the dilaton. A black hole, arising in such
theories, is supposed to be enclosed in a cavity, where it attains thermal
equilibrium, whereas outside the cavity the field is in the Boulware state. We
calculate quantum corrections to the Hawking temperature , with the
contribution from the boundary taken into account. Vacuum polarization outside
the shell tend to cool the system. We find that, for the shell to be in the
thermal equilibrium, it cannot be placed too close to the horizon. The quantum
corrections to the mass due to vacuum polarization vanish in spite of non-zero
quantum stresses. We discuss also the canonical boundary conditions and show
that accounting for the finiteness of the system plays a crucial role in some
theories (e.g., CGHS), where it enables to define the stable canonical
ensemble, whereas consideration in an infinite space would predict instability.Comment: 21 pages. In v.2 misprints corrected. To appear in Phys. Rev.
Coherent Acceleration of Material Wavepackets
We study the quantum dynamics of a material wavepacket bouncing off a
modulated atomic mirror in the presence of a gravitational field. We find the
occurrence of coherent accelerated dynamics for atoms. The acceleration takes
place for certain initial phase space data and within specific windows of
modulation strengths. The realization of the proposed acceleration scheme is
within the range of present day experimental possibilities.Comment: 6 pages, 3 figures, NASA "Quantum-to-Cosmos" conference proceedings
to be published in IJMP
Quantum-corrected ultraextremal horizons and validity of WKB in massless limit
We consider quantum backreaction of the quantized scalar field with an
arbitrary mass and curvature coupling on ultraextremal horizons. The problem is
distinguished in that (in contrast to non-extremal or extremal black holes) the
WKB approximation remains valid near (which is the radius of the
horizon) even in the massless limit. We examine the behavior of the
stress-energy tensor of the quantized field near and show that
quantum-corrected objects under discussion do exist. In the limit of the large
mass our results agree with previous ones known in literature.Comment: revtex4, 9 page
Phase transition between quantum and classical regimes for the escape rate of a biaxial spin system
Employing the method of mapping the spin problem onto a particle one, we have
derived the particle Hamiltonian for a biaxial spin system with a transverse or
longitudinal magnetic field. Using the Hamiltonian and introducing the
parameter where (U_{min})
corresponds to the top (bottom) of the potential and is the energy of the
particle, we have studied the first- or second-order transition around the
crossover temperature between thermal and quantum regimes for the escape rate,
depending on the anisotropy constant and the external magnetic field. It is
shown that the phase boundary separating the first- and second-order transition
and its crossover temperature are greatly influenced by the transverse
anisotropy constant as well as the transverse or longitudinal magnetic field.Comment: 5 pages + 3 figures, to be published in Phys. Rev.
Entropy of Quantum Fields for Nonextreme Black Holes in the Extreme Limit
Nonextreme black hole in a cavity within the framework of the canonical or
grand canonical ensemble can approach the extreme limit with a finite
temperature measured on a boundary located at a finite proper distance from the
horizon. In spite of this finite temperature, it is shown that the one-loop
contribution of quantum fields to the thermodynamic entropy due
to equilibrium Hawking radiation vanishes in the limit under consideration. The
same is true for the finite temperature version of the Bertotti-Robinson
spacetime into which a classical Reissner-Nordstr\"{o}m black hole turns in the
extreme limit. The result is attributed to the nature of a horizon
for the Bertotti-Robinson spacetime.Comment: 11 pages, ReVTeX, no figures. New references added, discussion
expanded, presentation and English improved. Accepted for publication in
Phys. Rev.
Coherent acceleration of material wavepackets in modulated optical fields
We study the quantum dynamics of a material wavepacket bouncing off a
modulated atomic mirror in the presence of a gravitational field. We find the
occurrence of coherent accelerated dynamics for atoms beyond the familiar
regime of dynamical localization. The acceleration takes place for certain
initial phase space data and within specific windows of modulation strengths.
The realization of the proposed acceleration scheme is within the range of
present day experimental possibilities
Thermodynamics of black holes with an infinite effective area of a horizon
In some kinds of classical dilaton theory there exist black holes with (i)
infinite horizon area or infinite (the coefficient at curvature in
Lagrangian) and (ii) zero Hawking temperature . For a generic static
black hole, without an assumption about spherical symmetry, we show that
infinite is compatible with a regularity of geometry in the case
only. We also point out that infinite is incompatible with the
regularity of a horizon of a generic static black hole, both for finite or
infinite . Direct application of the standard Euclidean approach in the case
of an infinite ''effective'' area of the horizon leads to
inconsistencies in the variational principle and gives for a black hole entropy
an indefinite expression, formally proportional to . We show
that treating a horizon as an additional boundary (that is, adding to the
action some terms calculated on the horizon) may restore self-consistency of
the variational procedure, if near the horizon grows not too rapidly. We
apply this approach to Brans-Dicke black holes and obtain the same answer S=0
as for ''usual'' (for example, Reissner-Nordstr\"{o}m) extreme classical black
holes. We also consider the exact solution for a conformal coupling, when
is finite but diverges and find that in the latter case both the standard
and modified approach give rise to an infinite action. Thus, this solution
represents a rare exception of a black hole without nontrivial thermal
properties.Comment: 24 pages. Accepted for publication in Class. Quant. Gra
Near-extremal and extremal quantum-corrected two-dimensional charged black holes
We consider charged black holes within dilaton gravity with
exponential-linear dependence of action coefficients on dilaton and minimal
coupling to quantum scalar fields. This includes, in particular, CGHS and RST
black holes in the uncharged limit. For non-extremal configuration quantum
correction to the total mass, Hawking temperature, electric potential and
metric are found explicitly and shown to obey the first generalized law. We
also demonstrate that quantum-corrected extremal black holes in these theories
do exist and correspond to the classically forbidden region of parameters in
the sense that the total mass ( is a charge). We show that in
the limit (where is the Hawking temperature) the mass and
geometry of non-extremal configuration go smoothly to those of the extremal
one, except from the narrow near-horizon region. In the vicinity of the horizon
the quantum-corrected geometry (however small quantum the coupling parameter
would be) of a non-extremal configuration tends to not the
quantum-corrected extremal one but to the special branch of solutions with the
constant dilaton (2D analog of the Bertotti-Robinson metric) instead.
Meanwhile, if exactly, the near-extremal configuration tends to the
extremal one. We also consider the dilaton theory which corresponds classically
to the spherically-symmetrical reduction from 4D case and show that for the
quantum-corrected extremal black hole .Comment: 25 pages. Typos corrected. To appear in Class. Quant. Gra
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