1,612 research outputs found
The basis of nonlocal curvature invariants in quantum gravity theory
A complete basis of nonlocal invariants in quantum gravity theory is built to
third order in spacetime curvature and matter-field strengths. The nonlocal
identities are obtained which reduce this basis for manifolds with
dimensionality . The present results are used in heat-kernel theory,
theory of gauge fields and serve as a basis for the model-independent approach
to quantum gravity and, in particular, for the study of nonlocal vacuum effects
in the gravitational collapse problem.Comment: 28 pages, REVTeX, Alberta Thy 14-9
Crossover between distinct mechanisms of microwave photoresistance in bilayer systems
We report on temperature-dependent magnetoresistance measurements in balanced
double quantum wells exposed to microwave irradiation for various frequencies.
We have found that the resistance oscillations are described by the
microwave-induced modification of electron distribution function limited by
inelastic scattering (inelastic mechanism), up to a temperature of T*~4 K. With
increasing temperature, a strong deviation of the oscillation amplitudes from
the behavior predicted by this mechanism is observed, presumably indicating a
crossover to another mechanism of microwave photoresistance, with similar
frequency dependence. Our analysis shows that this deviation cannot be fully
understood in terms of contribution from the mechanisms discussed in theory.Comment: 7 pages, 4 figure
Asymptotic behaviours of the heat kernel in covariant perturbation theory
The trace of the heat kernel is expanded in a basis of nonlocal curvature
invariants of th order. The coefficients of this expansion (the nonlocal
form factors) are calculated to third order in the curvature inclusive. The
early-time and late-time asymptotic behaviours of the trace of the heat kernel
are presented with this accuracy. The late-time behaviour gives the criterion
of analyticity of the effective action in quantum field theory. The latter
point is exemplified by deriving the effective action in two dimensions.Comment: 22 pages, REVTeX, Alberta Thy 45-9
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