92 research outputs found

### Amplifying the Hawking signal in BECs

We consider simple models of Bose-Einstein condensates to study analog
pair-creation effects, namely the Hawking effect from acoustic black holes and
the dynamical Casimir effect in rapidly time-dependent backgrounds. We also
focus on a proposal by Cornell to amplify the Hawking signal in density-density
correlators by reducing the atoms' interactions shortly before measurements are
made.Comment: 10 pages, 3 figures; to appear in Advances in High Energy Physics,
special Issue 'Experimental Tests of Quantum Gravity and Exotic Quantum Field
Theory Effects

### Hawking effect in BECs acoustic white holes

Bogoliubov pseudoparticle creation in a BEC undergoing a WH like flow is
investigated analytically in the case of a one dimensional geometry with
stepwise homogeneous regions. Comparison of the results with those
corresponding to a BH flow is performed. The implications for the analogous
gravitational problem is discussed.Comment: 29 pages, 32 figure

### 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

### 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.

### Numerical analysis of backreaction in acoustic black holes

Using methods of Quantum Field Theory in curved spacetime, the first order in
hbar quantum corrections to the motion of a fluid in an acoustic black hole
configuration are numerically computed. These corrections arise from the non
linear backreaction of the emitted phonons. Time dependent (isolated system)
and equilibrium configurations (hole in a sonic cavity) are both analyzed.Comment: 7 pages, 5 figure

### Classical and Quantum Shell Dynamics, and Vacuum Decay

Following a minisuperspace approach to the dynamics of a spherically
symmetric shell, a reduced Lagrangian for the radial degree of freedom is
derived directly from the Einstein-Hilbert action. The key feature of this new
Lagrangian is its invariance under time reparametrization. Indeed, all
classical and quantum dynamics is encoded in the Hamiltonian constraint that
follows from that invariance. Thus, at the classical level, we show that the
Hamiltonian constraint reproduces, in a simple gauge, Israel's matching
condition which governs the evolution of the shell. In the quantum case, the
vanishing of the Hamiltonian (in a weak sense), is interpreted as the
Wheeler-DeWitt equation for the physical states, in analogy to the
corresponding case in quantum cosmology. Using this equation, quantum tunneling
through the classical barrier is then investigated in the WKB approximation,
and the connection to vacuum decay is elucidated.Comment: 36 pages, ReVTeX, 10 Figs. in postscript format, in print on Class.&
Quant.Gra

### 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

### Backreaction in Acoustic Black Holes

The backreaction equations for the linearized quantum fluctuations in an
acoustic black hole are given. The solution near the horizon, obtained within a
dimensional reduction, indicates that acoustic black holes, unlike
Schwarzschild ones, get cooler as they radiate phonons. They show remarkable
analogies with near-extremal Reissner-Nordstrom black holes.Comment: 4 pages, revtex, 1 figure. revised version, published in pr

### Fourth derivative gravity in the auxiliary fields representation and application to the black hole stability

We consider an auxiliary fields formulation for the general fourth-order
gravity on an arbitrary curved background. The case of a Ricci-flat background
is elaborated in full details and it is shown that there is an equivalence with
the standard metric formulation. At the same time, using auxiliary fields helps
to make perturbations to look simpler and the results more clear. As an
application we reconsider the linear perturbations for the classical
Schwarzschild solution. We also briefly discuss the relation to the effect of
massive unphysical ghosts in the theory.Comment: 11 pages, no figure

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