1,245 research outputs found
Regularization of fluctuations near the sonic horizon due to the quantum potential and its influence on the Hawking radiation
We consider dynamics of fluctuations in transonically accelerating
Bose-Einstein condensates and luminous liquids (coherent light propagating in a
Kerr nonlinear medium) using the hydrodynamic approach. It is known that
neglecting the quantum potential (QP) leads to a singular behavior of quantum
and classical fluctuations in the vicinity of the Mach (sonic) horizon, which
in turn gives rise to the Hawking radiation. The neglect of QP is well founded
at not too small distances from the horizon, where is the
healing length. Taking the QP into account we show that a second characteristic
length exists, such that the linear fluctuation modes become
regularized for . At the modes keep their singular
behavior, which however is influenced by the QP. As a result we find a
deviation of the high frequency tail of the spectrum of Hawking radiation from
Planck's black body radiation distribution. Similar results hold for the wave
propagation in Kerr nonlinear media where the length and exist due
to the nonlinearity.Comment: 23 pages, 2 figure
Analog black holes in flowing dielectrics
We show that a flowing dielectric medium with a linear response to an
external electric field can be used to generate an analog geometry that has
many of the formal properties of a Schwarzschild black hole for light rays, in
spite of birefringence. We also discuss the possibility of generating these
analog black holes in the laboratory.Comment: Revtex4 file, 7 pages, 4 eps figures, a few changes in presentation,
some references added, conclusions unchange
Superradiant scattering from a hydrodynamic vortex
We show that sound waves scattered from a hydrodynamic vortex may be
amplified. Such superradiant scattering follows from the physical analogy
between spinning black holes and hydrodynamic vortices. However a sonic horizon
analogous to the black hole event horizon does not exist unless the vortex
possesses a central drain, which is challenging to produce experimentally. In
the astrophysical domain, superradiance can occur even in the absence of an
event horizon: we show that in the hydrodynamic analogue, a drain is not
required and a vortex scatters sound superradiantly. Possible experimental
realization in dilute gas Bose-Einstein condensates is discussed.Comment: 10 pages, 1 figur
Black hole lasers, a mode analysis
We show that the black hole laser effect discovered by Corley & Jacobson
should be described in terms of frequency eigenmodes that are spatially bound.
The spectrum contains a discrete and finite set of complex frequency modes
which appear in pairs and which encode the laser effect. In addition, it
contains real frequency modes that form a continuous set when space is
infinite, and which are only elastically scattered, i.e., not subject to any
Bogoliubov transformation. The quantization is straightforward, but the
calculation of the asymptotic fluxes is rather involved. When the number of
complex frequency modes is small, our expressions differ from those given
earlier. In particular, when the region between the horizons shrinks, there is
a minimal distance under which no complex frequency mode exists, and no
radiation is emitted. Finally, we relate this effect to other dynamical
instabilities found for rotating black holes and in electric fields, and we
give the conditions to get this type of instability.Comment: 19 pages, 3 figures, main changes: new figure and new Sec.6
`conditions for having a laser effect', final version accepted in PR
Analogue Cosmological Particle Creation: Quantum Correlations in Expanding Bose Einstein Condensates
We investigate the structure of quantum correlations in an expanding Bose
Einstein Condensate (BEC) through the analogue gravity framework. We consider
both a 3+1 isotropically expanding BEC as well as the experimentally relevant
case of an elongated, effectively 1+1 dimensional, expanding condensate. In
this case we include the effects of inhomogeneities in the condensate, a
feature rarely included in the analogue gravity literature. In both cases we
link the BEC expansion to a simple model for an expanding spacetime and then
study the correlation structure numerically and analytically (in suitable
approximations). We also discuss the expected strength of such correlation
patterns and experimentally feasible BEC systems in which these effects might
be detected in the near future.Comment: Reference adde
Entanglement Entropy in Critical Phenomena and Analogue Models of Quantum Gravity
A general geometrical structure of the entanglement entropy for spatial
partition of a relativistic QFT system is established by using methods of the
effective gravity action and the spectral geometry. A special attention is
payed to the subleading terms in the entropy in different dimensions and to
behaviour in different states. It is conjectured, on the base of relation
between the entropy and the action, that in a fundamental theory the ground
state entanglement entropy per unit area equals , where is the
Newton constant in the low-energy gravity sector of the theory. The conjecture
opens a new avenue in analogue gravity models. For instance, in higher
dimensional condensed matter systems, which near a critical point are described
by relativistic QFT's, the entanglement entropy density defines an effective
gravitational coupling. By studying the properties of this constant one can get
new insights in quantum gravity phenomena, such as the universality of the
low-energy physics, the renormalization group behavior of , the
statistical meaning of the Bekenstein-Hawking entropy.Comment: 13 pages, published version, minor changes in the abstract, new
reference
Dispersive fields in de Sitter space and event horizon thermodynamics
When Lorentz invariance is violated at high energy, the laws of black hole
thermodynamics are apparently no longer satisfied. To shed light on this
observation, we study dispersive fields in de Sitter space. We show that the
Bunch-Davies vacuum state restricted to the static patch is no longer thermal,
and that the Tolman law is violated. However we also show that, for free fields
at least, this vacuum is the only stationary stable state, as if it were in
equilibrium. We then present a precise correspondence between dispersive
effects found in de Sitter and in black hole metrics. This indicates that the
consequences of dispersion on thermodynamical laws could also be similar.Comment: 19 pages. Black and White version on Phys.Rev.D serve
Emergent Horizons in the Laboratory
The concept of a horizon known from general relativity describes the loss of
causal connection and can be applied to non-gravitational scenarios such as
out-of-equilibrium condensed-matter systems in the laboratory. This analogy
facilitates the identification and theoretical study (e.g., regarding the
trans-Planckian problem) and possibly the experimental verification of "exotic"
effects known from gravity and cosmology, such as Hawking radiation.
Furthermore, it yields a unified description and better understanding of
non-equilibrium phenomena in condensed matter systems and their universal
features. By means of several examples including general fluid flows, expanding
Bose-Einstein condensates, and dynamical quantum phase transitions, the
concepts of event, particle, and apparent horizons will be discussed together
with the resulting quantum effects.Comment: 7 pages, 4 figure
Isolation of high quality graphene from Ru by solution phase intercalation
2013 AIP Publishing LL
Fundamental limitations on "warp drive" spacetimes
"Warp drive" spacetimes are useful as "gedanken-experiments" that force us to
confront the foundations of general relativity, and among other things, to
precisely formulate the notion of "superluminal" communication. We verify the
non-perturbative violation of the classical energy conditions of the Alcubierre
and Natario warp drive spacetimes and apply linearized gravity to the
weak-field warp drive, testing the energy conditions to first and second order
of the non-relativistic warp-bubble velocity. We are primarily interested in a
secondary feature of the warp drive that has not previously been remarked upon,
if it could be built, the warp drive would be an example of a "reaction-less
drive". For both the Alcubierre and Natario warp drives we find that the
occurrence of significant energy condition violations is not just a high-speed
effect, but that the violations persist even at arbitrarily low speeds.
An interesting feature of this construction is that it is now meaningful to
place a finite mass spaceship at the center of the warp bubble, and compare the
warp field energy with the mass-energy of the spaceship. There is no hope of
doing this in Alcubierre's original version of the warp-field, since by
definition the point in the center of the warp bubble moves on a geodesic and
is "massless". That is, in Alcubierre's original formalism and in the Natario
formalism the spaceship is always treated as a test particle, while in the
linearized theory we can treat the spaceship as a finite mass object. For both
the Alcubierre and Natario warp drives we find that even at low speeds the net
(negative) energy stored in the warp fields must be a significant fraction of
the mass of the spaceship.Comment: 18 pages, Revtex4. V2: one reference added, some clarifying comments
and discussion, no physics changes, accepted for publication in Classical and
Quantum Gravit
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