1,107 research outputs found
Hawking-like radiation does not require a trapped region
We discuss the issue of quasi-particle production by ``analogue black holes''
with particular attention to the possibility of reproducing Hawking radiation
in a laboratory. By constructing simple geometric acoustic models, we obtain a
somewhat unexpected result: We show that in order to obtain a stationary and
Planckian emission of quasi-particles, it is not necessary to create a trapped
region in the acoustic spacetime (corresponding to a supersonic regime in the
fluid flow). It is sufficient to set up a dynamically changing flow
asymptotically approaching a sonic regime with sufficient rapidity in
laboratory time.Comment: revtex4, 4 pages, 1 figur
Stability analysis of sonic horizons in Bose-Einstein condensates
We examine the linear stability of various configurations in Bose-Einstein
condensates with sonic horizons. These configurations are chosen in analogy
with gravitational systems with a black hole horizon, a white hole horizon and
a combination of both. We discuss the role of different boundary conditions in
this stability analysis, paying special attention to their meaning in
gravitational terms. We highlight that the stability of a given configuration,
not only depends on its specific geometry, but especially on these boundary
conditions. Under boundary conditions directly extrapolated from those in
standard General Relativity, black hole configurations, white hole
configurations and the combination of both into a black hole--white hole
configuration are shown to be stable. However, we show that under other (less
stringent) boundary conditions, configurations with a single black hole horizon
remain stable, whereas white hole and black hole--white hole configurations
develop instabilities associated to the presence of the sonic horizons.Comment: 14 pages, 7 figures (reduced resolution
Naturalness in emergent spacetime
Effective field theories (EFTs) have been widely used as a framework in order
to place constraints on the Planck suppressed Lorentz violations predicted by
various models of quantum gravity. There are however technical problems in the
EFT framework when it comes to ensuring that small Lorentz violations remain
small -- this is the essence of the "naturalness" problem. Herein we present an
"emergent" space-time model, based on the "analogue gravity'' programme, by
investigating a specific condensed-matter system that is in principle capable
of simulating the salient features of an EFT framework with Lorentz violations.
Specifically, we consider the class of two-component BECs subject to
laser-induced transitions between the components, and we show that this model
is an example for Lorentz invariance violation due to ultraviolet physics.
Furthermore our model explicitly avoids the "naturalness problem", and makes
specific suggestions regarding how to construct a physically reasonable quantum
gravity phenomenology.Comment: V1:4 pages, revtex4; V2: slight changes in title, presentation, and
conclusions. This version to appear in Physical Review Letter
Sensitivity of Hawking radiation to superluminal dispersion relations
We analyze the Hawking radiation process due to collapsing configurations in
the presence of superluminal modifications of the dispersion relation. With
such superluminal dispersion relations, the horizon effectively becomes a
frequency-dependent concept. In particular, at every moment of the collapse,
there is a critical frequency above which no horizon is experienced. We show
that, as a consequence, the late-time radiation suffers strong modifications,
both quantitative and qualitative, compared to the standard Hawking picture.
Concretely, we show that the radiation spectrum becomes dependent on the
measuring time, on the surface gravities associated with different frequencies,
and on the critical frequency. Even if the critical frequency is well above the
Planck scale, important modifications still show up.Comment: 14 pages, 7 figures. Extensive paragraph added in conclusions to
clarify obtained result
Quasi-particle creation by analogue black holes
We discuss the issue of quasi-particle production by ``analogue black holes''
with particular attention to the possibility of reproducing Hawking radiation
in a laboratory. By constructing simple geometric acoustic models, we obtain a
somewhat unexpected result: We show that in order to obtain a stationary and
Planckian emission of quasi-particles, it is not necessary to create an
ergoregion in the acoustic spacetime (corresponding to a supersonic regime in
the flow). It is sufficient to set up a dynamically changing flow either
eventually generating an arbitrarily small sonic region v=c, but without any
ergoregion, or even just asymptotically, in laboratory time, approaching a
sonic regime with sufficient rapidity.Comment: 30 pages, 16 figure
Simulation of Acoustic Black Hole in a Laval Nozzle
A numerical simulation of fluid flows in a Laval nozzle is performed to
observe formations of acoustic black holes and the classical counterpart to
Hawking radiation under a realistic setting of the laboratory experiment. We
determined the Hawking temperature of the acoustic black hole from obtained
numerical data. Some noteworthy points in analyzing the experimental data are
clarified through our numerical simulation.Comment: 26 pages, published versio
Propagation in the atmosphere of ultrahigh-energy charmed hadrons
Charmed mesons may be produced when a primary cosmic ray or the leading
hadron in an air shower collide with an atmospheric nucleon. At energies \ge
10^8 GeV their decay length becomes larger than 10 km, which implies that they
tend to interact in the air instead of decaying. We study the collisions of
long-lived charmed hadrons in the atmosphere. We show that (\Lambda_c,D)-proton
diffractive processes and partonic collisions of any q^2 where the charm quark
is an spectator have lower inelasticity than (p,\pi)-proton collisions. In
particular, we find that a D meson deposits in each interaction just around 55%
of the energy deposited by a pion. On the other hand, collisions involving the
valence c quark (its annihilation with a sea cbar quark in the target or
c-quark exchange in the t channel) may deposit most of D meson energy, but
their frequency is low (below 0.1% of inelastic interactions). As a
consequence, very energetic charmed hadrons may keep a significant fraction of
their initial energy after several hadronic interactions, reaching much deeper
in the atmosphere than pions or protons of similar energy.Comment: 13 pages, version to appear in PR
Classical and Quantum Correlations of Scalar Field in the Inflationary Universe
We investigate classical and quantum correlations of a quantum field in the
inflationary universe using a particle detector model. By considering the
entanglement and correlations between two comoving detectors interacting with a
scalar field, we find that the entanglement between the detectors becomes zero
after their physical separation exceeds the Hubble horizon. Furthermore, the
quantum discord, which is defined as the quantum part of total correlation,
approaches zero on super horizon scale. These behaviors support appearance of
classical nature of the quantum fluctuation generated during the inflationary
era.Comment: 21 pages, accepted for publication in Phys. Rev.
Time-resolved density correlations as probe of squeezing in toroidal Bose-Einstein condensates
I study the evolution of mean field and linear quantum fluctuations in a
toroidal Bose-Einstein condensate, whose interaction strength is quenched from
a finite (repulsive) value to zero. The azimuthal equal-time density-density
correlation function is calculated and shows temporal oscillations with twice
the (final) excitation frequencies after the transition. These oscillations are
a direct consequence of positive and negative frequency mixing during
non-adiabatic evolution. I will argue that a time-resolved measurement of the
equal-time density correlator might be used to calculate the moduli of the
Bogoliubov coefficients and thus the amount of squeezing imposed on a mode,
i.e., the number of atoms excited out of the condensate.Comment: 18 pages, IOP styl
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