1,279 research outputs found
Particle production and reheating in the inflationary universe
Thermal field theory is applied to particle production rates in inflationary
models, leading to new results for catalysed, or two-stage decay, where massive
fields act as decay channels for the production of light fields. A numerical
investigation of the Bolztmann equation in an expanding universe shows that the
particle distributions produced during small amplitude inflaton oscillations or
alongside slowly moving inflaton fields can thermalise.Comment: 16 pages, 12 figures, LaTeX, extra references in v
Ultraviolet Divergences in Cosmological Correlations
A method is developed for dealing with ultraviolet divergences in
calculations of cosmological correlations, which does not depend on dimensional
regularization. An extended version of the WKB approximation is used to analyze
the divergences in these calculations, and these divergences are controlled by
the introduction of Pauli--Villars regulator fields. This approach is
illustrated in the theory of a scalar field with arbitrary self-interactions in
a fixed flat-space Robertson--Walker metric with arbitrary scale factor .
Explicit formulas are given for the counterterms needed to cancel all
dependence on the regulator properties, and an explicit prescription is given
for calculating finite regulator-independent correlation functions. The
possibility of infrared divergences in this theory is briefly considered.Comment: References added on various regularization methods. Improved
discussion of further issues. 26 pages, 1 figur
Radial geodesics as a microscopic origin of black hole entropy. I: Confined under the Schwarzschild horizon
Causal radial geodesics with a positive interval in the Schwarzschild metric
include a subset of trajectories completely confined under a horizon, which
compose a thermal statistical ensemble with the Hawking-Gibbons temperature.
The Bekenstein--Hawking entropy is given by an action at corresponding
geodesics of particles with a summed mass equal to that of black hole in the
limit of large mass.Comment: 16 pages, 12 eps-figures, iopart class, tought experiment (p.7) adde
Detecting many-body entanglements in noninteracting ultracold atomic fermi gases
We explore the possibility of detecting many-body entanglement using
time-of-flight (TOF) momentum correlations in ultracold atomic fermi gases. In
analogy to the vacuum correlations responsible for Bekenstein-Hawking black
hole entropy, a partitioned atomic gas will exhibit particle-hole correlations
responsible for entanglement entropy. The signature of these momentum
correlations might be detected by a sensitive TOF type experiment.Comment: 5 pages, 5 figures, fixed axes labels on figs. 3 and 5, added
reference
Dilution of zero point energies in the cosmological expansion
The vacuum fluctuations of all quantum fields filling the universe are
supposed to leave enormous energy and pressure contributions which are
incompatible with observations. It has been recently suggested that, when the
effective nature of quantum field theories is properly taken into account,
vacuum fluctuations behave as a relativistic gas rather than as a cosmological
constant. Accordingly, zero-point energies are tremendously diluted by the
universe expansion but provide an extra contribution to radiation energy.
Ongoing and future cosmological observations could offer the opportunity to
scrutinize this scenario. The presence of such additional contribution to
radiation energy can be tested by using primordial nucleosynthesis bounds or
measured on Cosmic Background Radiation anisotropy.Comment: 8 pages, no figures. Submitted the 17th of March to Modern Physics
Letters
The Gauge Fields and Ghosts in Rindler Space
We consider 2d Maxwell system defined on the Rindler space with metric
ds^2=\exp(2a\xi)\cdot(d\eta^2-d\xi^2) with the goal to study the dynamics of
the ghosts. We find an extra contribution to the vacuum energy in comparison
with Minkowski space time with metric ds^2= dt^2-dx^2. This extra contribution
can be traced to the unphysical degrees of freedom (in Minkowski space). The
technical reason for this effect to occur is the property of Bogolubov's
coefficients which mix the positive and negative frequencies modes. The
corresponding mixture can not be avoided because the projections to positive
-frequency modes with respect to Minkowski time t and positive -frequency modes
with respect to the Rindler observer's proper time \eta are not equivalent. The
exact cancellation of unphysical degrees of freedom which is maintained in
Minkowski space can not hold in the Rindler space. In BRST approach this effect
manifests itself as the presence of BRST charge density in L and R parts. An
inertial observer in Minkowski vacuum |0> observes a universe with no net BRST
charge only as a result of cancellation between the two. However, the Rindler
observers who do not ever have access to the entire space time would see a net
BRST charge. In this respect the effect resembles the Unruh effect. The effect
is infrared (IR) in nature, and sensitive to the horizon and/or boundaries. We
interpret the extra energy as the formation of the "ghost condensate" when the
ghost degrees of freedom can not propagate, but nevertheless do contribute to
the vacuum energy. Exact computations in this simple 2d model support the claim
made in [1] that the ghost contribution might be responsible for the observed
dark energy in 4d FLRW universe.Comment: Final version to appear in Phys. Rev. D. Comments on relation with
energy momentum computations and few new refs are adde
Collapse of Vacuum Bubbles in a Vacuum
Motivated by the discovery of a plenitude of metastable vacua in a string
landscape and the possibility of rapid tunneling between these vacua, we
revisit the dynamics of a false vacuum bubble in a background de Sitter
spacetime. We find that there exists a large parameter space that allows the
bubble to collapse into a black hole or to form a wormhole. This may have
interesting implications to inflationary physics.Comment: 8 pages including 6 figures, LaTex; references adde
Calculating the local-type fNL for slow-roll inflation with a non-vacuum initial state
Single-field slow-roll inflation with a non-vacuum initial state has an
enhanced bispectrum in the local limit. We numerically calculate the local-type
fNL signal in the CMB that would be measured for such models (including the
full transfer function and 2D projection). The nature of the result depends on
several parameters, including the occupation number N_k, the phase angle
\theta_k between the Bogoliubov parameters, and the slow-roll parameter
\epsilon. In the most conservative case, where one takes \theta_k \approx
\eta_0 k (justified by physical reasons discussed within) and \epsilon\lesssim
0.01, we find that 0 < fNL < 1.52 (\epsilon/0.01), which is likely too small to
be detected in the CMB. However, if one is willing to allow a constant value
for the phase angle \theta_k and N_k=O(1), fNL can be much larger and/or
negative (depending on the choice of \theta_k), e.g. fNL \approx 28
(\epsilon/0.01) or -6.4 (\epsilon/0.01); depending on \epsilon, these scenarios
could be detected by Planck or a future satellite. While we show that these
results are not actually a violation of the single-field consistency relation,
they do produce a value for fNL that is considerably larger than that usually
predicted from single-field inflation.Comment: 8 pages, 1 figure. v2: Version accepted for publication in PRD. Added
greatly expanded discussion of the phase angle \theta_k; this allows the
possibility of enhanced fNL, as mentioned in abstract. More explicit
comparisons with earlier wor
Minimal conductivity of rippled graphene with topological disorder
We study the transport properties of a neutral graphene sheet with curved
regions induced or stabilized by topological defects. The proposed model gives
rise to Dirac fermions in a random magnetic field and in the random space
dependent Fermi velocity induced by the curvature. This last term leads to
singular long range correlated disorder with special characteristics. The Drude
minimal conductivity at zero energy is found to be inversely proportional to
the density of topological disorder, a signature of diffusive behavior.Comment: 12 pages, no figure
Infra-red effects of Non-linear sigma model in de Sitter space
We extend our investigation on a possible de Sitter symmetry breaking
mechanism in non-linear sigma models. The scale invariance of the quantum
fluctuations could make the cosmological constant time dependent signaling the
de Sitter symmetry breaking. To understand such a symmetry breaking mechanism,
we investigate the energy-momentum tensor. We show that the leading infra-red
logarithms cancel to all orders in perturbation theory in a generic non-linear
sigma model. When the target space is an N sphere, the de Sitter symmetry is
preserved in the large N limit. For a less symmetric target space, the
infra-red logarithms appear at the three loop level. However there is a counter
term to precisely cancel it. The leading infra-red logarithms do not cancel for
higher derivative interactions. We investigate such a model in which the
infra-red logarithms first appear at the three loop level. A nonperturbative
investigation in the large N limit shows that they eventually grow as large as
the one loop effect.Comment: 39page
- …