901 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

### The depletion in Bose Einstein condensates using Quantum Field Theory in curved space

Using methods developed in Quantum Field Theory in curved space we can
estimate the effects of the inhomogeneities and of a non vanishing velocity on
the depletion of a Bose Einstein condensate within the hydrodynamical
approximation.Comment: 4 pages, no figure. Discussion extended and 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

### Quantum Effects in Black Hole Interiors

The Weyl curvature inside a black hole formed in a generic collapse grows,
classically without bound, near to the inner horizon, due to partial absorption
and blueshifting of the radiative tail of the collapse. Using a spherical
model, we examine how this growth is modified by quantum effects of conformally
coupled massless fields.Comment: 13 pages, 1 figure (not included), RevTe

### Low frequency gray-body factors and infrared divergences: rigorous results

Formal solutions to the mode equations for both spherically symmetric black
holes and Bose-Einstein condensate acoustic black holes are obtained by writing
the spatial part of the mode equation as a linear Volterra integral equation of
the second kind. The solutions work for a massless minimally coupled scalar
field in the s-wave or zero angular momentum sector for a spherically symmetric
black hole and in the longitudinal sector of a 1D Bose-Einstein condensate
acoustic black hole. These solutions are used to obtain in a rigorous way
analytic expressions for the scattering coefficients and gray-body factors in
the zero frequency limit. They are also used to study the infrared behaviors of
the symmetric two-point function and two functions derived from it: the
point-split stress-energy tensor for the massless minimally coupled scalar
field in Schwarzschild-de Sitter spacetime and the density-density correlation
function for a Bose-Einstein condensate acoustic black hole.Comment: 41 pages, 5 figure

### Scattering coefficients and gray-body factor for 1D BEC acoustic black holes: exact results

A complete set of exact analytic solutions to the mode equation is found in
the region exterior to the acoustic horizon for a class of 1D Bose-Einstein
condensate (BEC) acoustic black holes. From these, analytic expressions for the
scattering coefficients and gray-body factor are obtained. The results are used
to verify previous predictions regarding the behaviors of the scattering
coefficients and gray-body factor in the low frequency limit.Comment: 13 pages, 1 figure, Final version, to appear in Phys. Rev.

### Hawking radiation of massive modes and undulations

We compute the analogue Hawking radiation for modes which posses a small wave
vector perpendicular to the horizon. For low frequencies, the resulting mass
term induces a total reflection. This generates an extra mode mixing that
occurs in the supersonic region, which cancels out the infrared divergence of
the near horizon spectrum. As a result, the amplitude of the undulation
(0-frequency wave with macroscopic amplitude) emitted in white hole flows now
saturates at the linear level, unlike what was recently found in the massless
case. In addition, we point out that the mass introduces a new type of
undulation which is produced in black hole flows, and which is well described
in the hydrodynamical regime.Comment: 37 pages, 8 figures, published versio

### 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

### Gray-body factor and infrared divergences in 1D BEC acoustic black holes

It is shown that the gray-body factor for a one-dimensional elongated
Bose-Einstein condensate (BEC) acoustic black hole with one horizon does not
vanish in the low-frequency ($\omega\to 0$) limit. This implies that the analog
Hawking radiation is dominated by the emission of an infinite number
($\frac{1}{\omega}$) of soft phonons in contrast with the case of a
Schwarzschild black hole where the gray-body factor vanishes as $\omega\to 0$
and the spectrum is not dominated by low-energy particles. The infrared
behaviors of certain correlation functions are also discussed.Comment: 6 pages, 2 figures. Final version. A double misprint in Eq. (21) of
the published version has been corrected her

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