60 research outputs found
Classical radiation by free-falling charges in de Sitter spacetime
We study the classical radiation emitted by free-falling charges in de Sitter
spacetime coupled to different kinds of fields. Specifically we consider the
cases of the electromagnetic field, linearized gravity and scalar fields with
arbitrary mass and curvature coupling. Given an arbitrary set of such charges,
there is a generic result for sufficiently late times which corresponds to each
charge being surrounded by a field zone with negligible influence from the
other charges. Furthermore, we explicitly find a static solution in the static
patch adapted to a charge (implying no energy loss by the charge) which can be
regularly extended beyond the horizon to the full de Sitter spacetime, and show
that any other solution decays at late times to this one. On the other hand,
for non-conformal scalar fields the inertial observers naturally associated
with spatially flat coordinates will see a non-vanishing flux far from the
horizon, which will fall off more slowly than the inverse square of the
distance for sufficiently light fields (m^2 + \xi R < 5H^2/4) and give rise to
a total integrated flux that grows unboundedly with the radius. This can be
qualitatively interpreted as a consequence of a classical parametric
amplification of the field generated by the charge due to the time-dependent
background spacetime. Most of these results do not hold for massless minimally
coupled scalar fields, whose special behavior is analyzed separately.Comment: 31 pages, REVTeX4, minor changes, one reference added, version to
appear in Phys. Rev.
Notes on chiral hydrodynamics within effective theory approach
We address the issue of evaluating chiral effects (such as the newly
discovered chiral separation) in hydrodynamic approximation. The main tool we
use is effective theory which defines interaction in terms of chemical
potentials . In the lowest order in we reproduce recent
results based on thermodynamic considerations. In higher orders the results
depend on details of infrared cutoff. Another point of our interest is an
alternative way of the anomaly matching through introduction of effective
scalar fields arising in the hydrodynamic approximation
Jet Broadening in Flowing Matter -- Resummation
In this work, we obtain the leading corrections to the jet momentum
broadening distribution in a QCD medium arising from the transverse flow of the
matter. We first derive the single-particle propagator of a highly energetic
parton resumming its multiple interactions with the homogeneous flowing matter,
explicitly keeping the leading subeikonal flow terms. Then, we use this
propagator to obtain the jet broadening distribution and its leading moments.
We show that this distribution becomes anisotropic in the presence of
transverse flow, since its odd moments are generally non-zero and proportional
to the transverse velocity of the medium. Finally, we evaluate several odd
moments, which we compare to the corresponding results at first order in
opacity, showing that accounting for multiple in-medium scatterings is
essential to describe some observables in dense nuclear matter.Comment: 28 pages, 2 figure
Emission spectra of terahertz quantum cascade laser
We calculated energy levels, wave functions, and energies of radiative transitions in terahertz
quantum cascade lasers based on GaAs/Al0.15Ga0.85As heterostructures. Current-voltage characteristics
and current dependences of laser radiation intensity were measured, and the maximum
operating temperatures reaching 85 K were determined. Radiation spectra of quantum cascade
lasers were measured for different temperatures, and the effect of intensity “pumping” from lowfrequency
modes to high-frequency modes was found to happen in the case of an increase in the
current and time delay of the signal capture, which is explained by heating of the sample during
a pulse of the current. Application of the lasers for registration of impurity photoconductivity
signals in semiconductor heterostructures was demonstrated
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