2,322 research outputs found
Trace Anomaly of Dilaton Coupled Scalars in Two Dimensions
Conformal scalar fields coupled to the dilaton appear naturally in
two-dimensional models of black hole evaporation. We calculate their trace
anomaly. It follows that an RST-type counterterm appears naturally in the
one-loop effective action.Comment: 11 pages, LaTeX2e; submitted to Phys. Rev. Lett., minor change
Trace anomaly and Hawking effect in generic 2D dilaton gravity theories
Black hole solutions in the context of a generic matter-coupled
two-dimensional dilaton gravity theory are discussed both at the classical and
semiclassical level. Starting from general assumptions, a criterion for the
existence of black holes is given. The relationship between conformal anomaly
and Hawking radiation is extended to a broad class of two-dimensional dilaton
gravity models. A general and simple formula relating the magnitude of the
Hawking effect to the dilaton potential evaluated on the horizon is derived.Comment: 14 pages, Plain-Tex, 4 figures in a uuencoded-gzipcompressed ps fil
Conducting phase in the two-dimensional disordered Hubbard model
We study the temperature-dependent conductivity and spin
susceptibility of the two-dimensional disordered Hubbard model.
Calculations of the current-current correlation function using the Determinant
Quantum Monte Carlo method show that repulsion between electrons can
significantly enhance the conductivity, and at low temperatures change the sign
of from positive (insulating behavior) to negative (conducting
behavior). This result suggests the possibility of a metallic phase, and
consequently a metal-insulator transition,in a two-dimensional microscopic
model containing both interactions and disorder. The metallic phase is a
non-Fermi liquid with local moments as deduced from a Curie-like temperature
dependence of .Comment: 4 pages; 4 postscript figures; added (1) a new figure showing
temperature dependence of spin susceptibility; (2) more references. accepted
for publication in Phys. Rev. Let
Extremal single-charge small black holes: Entropy function analysis
We study stretched horizons of the type AdS_2 x S^8 for certain spherically
symmetric extremal small black holes in type IIA carrying only D0-brane charge
making use of Sen's entropy function formalism for higher derivative gravity. A
scaling argument is given to show that the entropy of this class of black holes
for large charge behaves as \sqrt{|q|} where q is the electric charge. The
leading order result arises from IIA string loop corrections. We find that for
solutions to exist the force on a probe D0-brane has to vanish and we prove
that this feature persists to all higher derivative orders. We comment on the
nature of the extremum of these solutions and on the sub-leading corrections to
the entropy. The entropy of other small black holes related by dualities to our
case is also discussed.Comment: 19 pages, v2:typos corrected and references adde
Do semiclassical zero temperature black holes exist?
The semiclassical Einstein equations are solved to first order in for the case of a Reissner-Nordstr\"{o}m black hole perturbed by the
vacuum stress-energy of quantized free fields. Massless and massive fields of
spin 0, 1/2, and 1 are considered. We show that in all physically realistic
cases, macroscopic zero temperature black hole solutions do not exist. Any
static zero temperature semiclassical black hole solutions must then be
microscopic and isolated in the space of solutions; they do not join smoothly
onto the classical extreme Reissner-Nordst\"{o}m solution as .Comment: 5 pages, no figures, minor changes and corrections, to appear in
Physical Review Letter
Superconductor-Insulator Transition in a Disordered Electronic System
We study an electronic model of a 2D superconductor with onsite randomness
using Quantum Monte Carlo simulations. The superfluid density is used to track
the destruction of superconductivity in the ground state with increasing
disorder. The non-superconducting state is identified as an insulator from the
temperature dependence of its d.c. resistivity. The value of
at the superconductor-insulator transition appears to be non-universal.Comment: PostScript, 4 pages, figures include
Non-singular four-dimensional black holes and the Jackiw-Teitelboim theory
A four-dimensional dilaton-gravity action whose spherical reduction to two
dimensions leads to the Jackiw-Teitelboim theory is presented. A nonsingular
black hole solution of the theory is obtained and its physical interpretation
is discussed. The classical and semiclassical properties of the solution and of
its 2d counterpart are analysed. The 2d theory is also used to model the
evaporation process of the near-extremal 4d black hole. We describe in detail
the peculiarities of the black hole solutions, in particular the purely
topological nature of the Hawking radiation, in the context of the
Jackiw-Teitelboim theory.Comment: 24 pages, 6 figures available upon request, Plain Tex,
INFN-CA-TH-94-2
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
Semiclassical Extremal Blackholes
Extremal black holes are studied in a two dimensional model motivated by a
dimensional reduction from four dimensions. Their quantum corrected geometry is
calculated semiclassically and a mild singularity is shown to appear at the
horizon.
Extensions of the geometry past the horizon are not unique but there are
continuations free from malevolent singularities. A few comments are made about
the relevance of these results to four dimensions and to the study of black
hole entropy and information loss.Comment: 16 pages, 2 figures upon request, CALT-68-1833 - (new version
corrects omissions in previous list of references
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