7,028 research outputs found
Soluble models in 2d dilaton gravity
A one-parameter class of simple models of two-dimensional dilaton gravity,
which can be exactly solved including back-reaction effects, is investigated at
both classical and quantum levels. This family contains the RST model as a
special case, and it continuously interpolates between models having a flat
(Rindler) geometry and a constant curvature metric with a non-trivial dilaton
field. The processes of formation of black hole singularities from collapsing
matter and Hawking evaporation are considered in detail. Various physical
aspects of these geometries are discussed, including the cosmological
interpretation.Comment: 15 pages, harvmac, 3 figure
A theory of quantum black holes: non-perturbative corrections and no-veil conjecture
A common belief is that further quantum corrections near the singularity of a
large black hole should not substantially modify the semiclassical picture of
black hole evaporation; in particular, the outgoing spectrum of radiation
should be very close to the thermal spectrum predicted by Hawking. In this
paper we explore a possible counterexample: in the context of dilaton gravity,
we find that non-perturbative quantum corrections which are important in strong
coupling regions may completely alter the semiclassical picture, to the extent
that the presumptive space-like boundary becomes time-like, changing in this
way the causal structure of the semiclassical geometry. As a result, only a
small fraction of the total energy is radiated outside the fake event horizon;
most of the energy comes in fact at later retarded times and there is no
information loss problem. Thus we propose that this may constitute a general
characteristic of quantum black holes, that is, quantum gravity might be such
as to prevent the formation of global event horizons. We argue that this is not
unnatural from the viewpoint of quantum mechanics.Comment: 24 pages, 12 figures (not included, available by request), UTTG-22-9
Black Hole Formation by Sine-Gordon Solitons in Two-dimensional Dilaton Gravity
The CGHS model of two-dimensional dilaton gravity coupled to a sine-Gordon
matter field is considered. The theory is exactly solvable classically, and the
solutions of a kink and two-kink type solitons are studied in connection with
black hole formation.Comment: 11 pages, no figures, revte
Quantitative Study of Magnetotransport through a (Ga,Mn)As Single Ferromagnetic Domain
We have performed a systematic investigation of the longitudinal and
transverse magnetoresistance of a single ferromagnetic domain in (Ga,Mn)As. We
find that, by taking into account the intrinsic dependence of the resistivity
on the magnetic induction, an excellent agreement between experimental results
and theoretical expectations is obtained. Our findings provide a detailed and
fully quantitative validation of the theoretical description of
magnetotransport through a single ferromagnetic domain. Our analysis
furthermore indicates the relevance of magneto-impurity scattering as a
mechanism for magnetoresistance in (Ga,Mn)As.Comment: 5 pages, 4 figures; v2: missing references included, figures
recompressed to improve readabilit
Quantum Theories of Dilaton Gravity
Quantization of two-dimensional dilaton gravity coupled to conformal matter
is investigated. Working in conformal gauge about a fixed background metric,
the theory may be viewed as a sigma model whose target space is parameterized
by the dilaton and conformal factor . A precise connection is
given between the constraint that the theory be independent of the background
metric and conformal invariance of the resulting sigma model. Although the
action is renormalizable, new coupling constants must be specified at each
order in perturbation theory in order to determine the quantum theory. These
constants may be viewed as initial data for the beta function equations. It is
argued that not all choices of this data correspond to physically sensible
theories of gravity, and physically motivated constraints on the data are
discussed. In particular a recently constructed subclass of initial data which
reduces the full quantum theory to a soluble Liouville-like theory has energies
unbounded from below and thus is unphysical. Possibilities for modifying this
construction so as to avoid this difficulty are briefly discussed.Comment: 20 pages (Major additions made, including 5 pages on the relation
between conformal invariance and background independence.
Critical energy flux and mass in solvable theories of 2d dilaton gravity
In this paper we address the issue of determining the semiclassical threshold
for black hole formation in the context of a one-parameter family of theories
which continuously interpolates between the RST and BPP models. We find that
the results depend significantly on the initial static configuration of the
spacetime geometry before the influx of matter is turned on. In some cases
there is a critical energy density, given by the Hawking rate of evaporation,
as well as a critical mass (eventually vanishing). In others there is
neither nor a critical flux.Comment: LaTeX file, 12 pages, 4 figure
Quantum Black Holes in Two Dimensions
We show that a whole class of quantum actions for dilaton-gravity, which
reduce to the CGHS theory in the classical limit, can be written as a
Liouville-like theory. In a sub-class of this, the field space singularity
observed by several authors is absent, regardless of the number of matter
fields, and in addition it is such that the dilaton-gravity functional
integration range (the real line) transforms into itself for the Liouville
theory fields. We also discuss some problems associated with the usual
calculation of Hawking radiation, which stem from the neglect of back reaction.
We give an alternative argument incorporating back reaction but find that the
rate is still asymptotically constant. The latter is due to the fact that the
quantum theory does not seem to have a lower bound in energy and Hawking
radiation takes positive Bondi (or ADM) mass solutions to arbitrarily large
negative mass.Comment: 28 pages, phyzzx, revised discussion of Hawking radiatio
Semiclassical Approach to Black Hole Evaporation
Black hole evaporation may lead to massive or massless remnants, or naked
singularities. This paper investigates this process in the context of two quite
different two dimensional black hole models. The first is the original CGHS
model, the second is another two dimensional dilaton-gravity model, but with
properties much closer to physics in the real, four dimensional, world.
Numerical simulations are performed of the formation and subsequent evaporation
of black holes and the results are found to agree qualitatively with the
exactly solved modified CGHS models, namely that the semiclassical
approximation breaks down just before a naked singularity appears.Comment: 15 pages, PUPT-1340, harvmac, 11 figures available on reques
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