1,151 research outputs found
4D quantum black hole physics from 2D models?
Minimally coupled 4D scalar fields in Schwarzschild space-time are
considered. Dimensional reduction to 2D leads to a well known anomaly induced
effective action, which we consider here in a local form with the introduction
of auxiliary fields. Boundary conditions are imposed on them in order to select
the appropriate quantum states (Boulware, Unruh annd Israel-Hartle-Hawking).
The stress tensor is then calculated and its comparison with the expected 4D
form turns out to be unsuccessful. We also critically discuss in some detail a
recent controversial result appeared in the literature on the same topic.Comment: latex, 13 pages; misprints corrected, references adde
Particle production and transplanckian problem on the non-commutative plane
We consider the coherent state approach to non-commutativity, and we derive
from it an effective quantum scalar field theory. We show how the
non-commutativity can be taken in account by a suitable modification of the
Klein-Gordon product, and of the equal-time commutation relations. We prove
that, in curved space, the Bogolubov coefficients are unchanged, hence the
number density of the produced particle is the same as for the commutative
case. What changes though is the associated energy density, and this offers a
simple solution to the transplanckian problem.Comment: Minor typos corrected, references added. Accepted for publication by
Modern Physics Letter
Effective dynamics of self-gravitating extended objects
We introduce an effective Lagrangian which describes the classical and
semiclassical dynamics of spherically symmetric, self-gravitating objects that
may populate the Universe at large and small (Planck) scale. These include
wormholes, black holes and inflationary bubbles. We speculate that such objects
represent some possible modes of fluctuation in the primordial spacetime foam
out of which our universe was born. Several results obtained by different
methods are encompassed and reinterpreted by our effective approach. As an
example, we discuss: i) the gravitational nucleation coefficient for a pair of
Minkowski bubbles, and ii) the nucleation coefficient of an inflationary vacuum
bubble in a Minkowski backgroundComment: 13 pages, no figures, ReVTe
Generalized Virasoro anomaly and stress tensor for dilaton coupled theories
We derive the anomalous transformation law of the quantum stress tensor for a
2D massless scalar field coupled to an external dilaton. This provides a
generalization of the Virasoro anomaly which turns out to be consistent with
the trace anomaly. We apply it together with the equivalence principle to
compute the expectation values of the covariant quantum stress tensor on a
curved background. Finally we briefly illustrate how to evaluate vacuum
polarization and Hawking radiation effects from these results.Comment: enlarged version of hep-th/0307096 containing the quantum stress
tensor for arbitrary geometries and discussion of the Hawking effect. To
appear in Phys. Lett.
Correlation patterns from massive phonons in 1+1 dimensional acoustic black holes: A toy model
Transverse excitations in analogue black holes induce a mass like term in the
longitudinal mode equation. With a simple toy model we show that correlation
functions display a rather rich structure characterized by groups of parallel
peaks. For the most part the structure is completely different from that found
in the massless case.Comment: 40 pages, 13 figures. Minor changes and corrections Phys. Rev. D
versio
A model of radiating black hole in noncommutative geometry
The phenomenology of a radiating Schwarzschild black hole is analyzed in a
noncommutative spacetime. It is shown that noncommutativity does not depend on
the intensity of the curvature. Thus we legitimately introduce noncommutativity
in the weak field limit by a coordinate coherent state approach. The new
interesting results are the following: i) the existence of a minimal non-zero
mass to which black hole can shrink; ii) a finite maximum temperature that the
black hole can reach before cooling down to absolute zero; iii) the absence of
any curvature singularity. The proposed scenario offers a possible solution to
conventional difficulties when describing terminal phase of black hole
evaporation.Comment: 10 pages, 4 figure
Hawking radiation from extremal and non-extremal black holes
The relationship between Hawking radiation emitted by non extremal and
extremal Reissner Nordstrom black holes is critically analyzed. A careful study
of a series of regular collapsing geometries reveals that the stress energy
tensor stays regular in the extremal limit and is smoothly connected to that of
non extremal black holes. The unexpected feature is that the late time
transients which played little role in the non extremal case are necessary to
preserve the well defined character of the flux in the extremal case. The known
singular behavior of the static energy density of extremal black holes is
recovered from our series by neglecting these transients, when performing what
turns out to be an illegitimate late time limit. Although our results are
derived in two dimensional settings, we explain why they should also apply to
higher dimensional black holes.Comment: 18 pages, late
Two-dimensional black holes in accelerated frames: quantum aspects
By considering charged black hole solutions of a one parameter family of two
dimensional dilaton gravity theories, one finds the existence of quantum
mechanically stable gravitational kinks with a simple mass to charge relation.
Unlike their Einsteinian counterpart (i.e. extreme Reissner-Nordstr\"om), these
have nonvanishing horizon surface gravity.Comment: 18 pages, harvmac, 2 figure
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