1,531 research outputs found
Entangled-photon generation in nano-to-bulk crossover regime
We have theoretically investigated a generation of entangled photons from
biexcitons in a semiconductor film with thickness in nano-to-bulk crossover
regime. In contrast to the cases of quantum dots and bulk materials, we can
highly control the generated state of entangled photons by the design of
peculiar energy structure of exciton-photon coupled modes in the thickness
range between nanometers and micrometers. Owing to the enhancement of radiative
decay rate of excitons at this thickness range, the statistical accuracy of
generated photon pairs can be increased beyond the trade-off problem with the
signal intensity. Implementing an optical cavity structure, the generation
efficiency can be enhanced with keeping the high statistical accuracy.Comment: 9 pages, 3 figure
Helical Magnetic Fields from Inflation
We analyze the generation of seed magnetic fields during de Sitter inflation
considering a non-invariant conformal term in the electromagnetic Lagrangian of
the form , where
is a pseudoscalar function of a non-trivial background field .
In particular, we consider a toy model, that could be realized owing to the
coupling between the photon and either a (tachyonic) massive pseudoscalar field
and a massless pseudoscalar field non-minimally coupled to gravity, where
follows a simple power-law behavior during
inflation, while it is negligibly small subsequently. Here, is a positive
dimensionless constant, the wavenumber, the conformal time, and
a real positive number. We find that only when and astrophysically interesting fields can be produced as
excitation of the vacuum, and that they are maximally helical.Comment: 17 pages, 1 figure, subsection IIc and references added; accepted for
publication in IJMP
A Note on Tsallis Holographic Dark Energy
We explore the effects of considering various infrared (IR) cutoffs,
including the particle horizon, Ricci horizon and Granda-Oliveros (GO) cutoffs,
on the properties of Tsallis holographic dark energy (THDE) model, proposed
inspired by Tsallis generalized entropy formalism \cite{THDE}. Interestingly
enough, we find that for the particle horizon as IR cutoff, the obtained THDE
model can describe the accelerated universe. This is in contrast to the usual
HDE model which cannot lead to an accelerated universe, if one consider the
particle horizon as IR cutoff. We also investigate the cosmological
consequences of THDE under the assumption of a mutual interaction between the
dark sectors of the Universe. It is shown that the evolution history of the
Universe can be described by these IR cutoffs and thus the current cosmic
acceleration can also been realized. The sound instability of THDE models for
each cutoff are also explored, separately.Comment: 12 pages, 31 figure
Generic estimates for magnetic fields generated during inflation including Dirac-Born-Infeld theories
We estimate the strength of large-scale magnetic fields produced during
inflation in the framework of Dirac-Born-Infeld (DBI) theories. This analysis
is sufficiently general in the sense that it covers most of conformal symmetry
breaking theories in which the electromagnetic field is coupled to a scalar
field. In DBI theories there is an additional factor associated with the speed
of sound, which allows a possibility to lead to an extra amplification of the
magnetic field in a ultra-relativistic region. We clarify the conditions under
which seed magnetic fields to feed the galactic dynamo mechanism at a
decoupling epoch as well as present magnetic fields on galactic scales are
sufficiently generated to satisfy observational bounds.Comment: 7 pages, no figure, accepted in Phys. Rev.
Traversable wormholes with static spherical symmetry and their stability in higher-curvature gravity
The solutions of traversable wormholes and their geometries are investigated
in higher-curvature gravity with boundary terms for each case under the
presence of anisotropic, isotropic and barotropic fluids in detail. For each
case, the effective energy-momentum tensor violates the null energy condition
throughout the wormhole throat. The null and weak energy conditions are also
analyzed for ordinary matters. The regions that physically viable wormhole
solutions can exist are explicitly shown. Furthermore, it is found that the
range of the viable regions exhibits an alternating pattern of expansion and
contraction. The present analyses can reveal the regions in which traversable
wormholes can be constructed for anisotropic, isotropic and barotropic fluids
cases with incorporating realistic matter contents, leading to fundamental
physics insights into the feasible construction of wormholes in
higher-curvature gravity with boundary term.Comment: 11 pages, 8 figure
- …