24,786 research outputs found
Vacuum polarization of a quantized scalar field in the thermal state in a long throat
Vacuum polarization of scalar fields in the background of a long throat is
investigated. The field is assumed to be both massive or massless, with
arbitrary coupling to the scalar curvature, and in a thermal state at an
arbitrary temperature. Analytical approximation for is obtained.Comment: 20 page
Analytical approximation for of a quantized scalar field in ultrastatic asymptotically flat spacetimes
Analytical approximations for of a quantized scalar field in
ultrastatic asymptotically flat spacetimes are obtained. The field is assumed
to be both massive and massless, with an arbitrary coupling $\xi$ to the scalar
curvature, and in a zero or nonzero temperature vacuum state. The expression
for is divided into low- and high-frequency parts. The expansion
for the high-frequency contribution to this quantity is obtained. This
expansion is analogous to the DeWitt-Schwinger one. As an example, the
low-frequency contribution to is calculated on the background of
the small perturbed flat spacetime in a quantum state corresponding to the
Minkowski vacuum at the asymptotic. The limits of the applicability of these
approximations are discussed.Comment: revtex4, 9 page
Interference at quantum transitions: lasing without inversion and resonant four-wave mixing in strong fields at Doppler-broadened transitions
An influence of nonlinear interference processes at quantum transitions under
strong resonance electromagnetic fields on absorption, amplification and
refractive indices as well as on four-wave mixing processes is investigated.
Doppler broadening of the coupled transitions, incoherent excitation,
relaxation processes, as well as power saturation processes associated with the
coupled levels are taken into account. Both closed (ground state is involved)
and open (only excited states are involved) energy level configurations are
considered. Common expressions are obtained which allow one to analyze the
optical characteristics (including gain without inversion and enhanced
refractive index at vanishing absorption) for various V, Lambda and H
configurations of interfering transitions by a simple substitution of
parameters. Similar expressions for resonant four-wave mixing in Raman
configurations are derived too. Crucial role of Doppler broadening is shown.
The theory is applied to numerical analysis of some recent and potential
experiments.Comment: 12 pages, 9 eps figures, invited paper, Proceedings of the 11th
International Vavilov Conference on Nonlinear Optic
Results from HARP and their implications for neutrino physics
Recent results from the HARP experiment on the measurements of the
double-differential production cross-section of pions in proton interactions
with beryllium, carbon and tantalum targets are presented. These results are
relevant for a detailed understanding of neutrino flux in accelerator neutrino
experiments MiniBooNE/SciBooNE, for a better prediction of atmospheric neutrino
fluxes as well as for an optimization of a future neutrino factory design.Comment: Presented at the XLIInd Rencontres de Moriond on Electroweak
Interactions and Unified Theorie
Stress-energy of a quantized scalar field in static wormhole spacetimes
An analytical approximation of for a quantized scalar field in
a static spherically symmetric spacetime with a topology is
obtained. The gravitational background is assumed slowly varying. The scalar
field is assumed to be both massive and massless, with an arbitrary coupling
to the scalar curvature and in a zero temperature vacuum state. It is
demonstrated that for some values of curvature coupling the stress-energy has
the properties needed to support the wormhole geometry.Comment: 21 pages, revte
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