939 research outputs found
Low energy Quantum Gravity from the Effective Average Action
Within the effective average action approach to quantum gravity, we recover
the low energy effective action as derived in the effective field theory
framework, by studying the flow of possibly non-local form factors that appear
in the curvature expansion of the effective average action. We restrict to the
one-loop flow where progress can be made with the aid of the non-local heat
kernel expansion. We discuss the possible physical implications of the scale
dependent low energy effective action through the analysis of the quantum
corrections to the Newtonian potential.Comment: 24 pages, 1 figure; minor corrections, references adde
Quantum corrections to the geodesic equation
In this talk we will argue that, when gravitons are taken into account, the
solution to the semiclassical Einstein equations (SEE) is not physical. The
reason is simple: any classical device used to measure the spacetime geometry
will also feel the graviton fluctuations. As the coupling between the classical
device and the metric is non linear, the device will not measure the
`background geometry' (i.e. the geometry that solves the SEE). As a particular
example we will show that a classical particle does not follow a geodesic of
the background metric. Instead its motion is determined by a quantum corrected
geodesic equation that takes into account its coupling to the gravitons. This
analysis will also lead us to find a solution to the so-called gauge fixing
problem: the quantum corrected geodesic equation is explicitly independent of
any gauge fixing parameter.Comment: Revtex file, 6 pages, no figures. Talk presented at the meeting
"Trends in Theoretical Physics II", Buenos Aires, Argentina, December 199
Casimir interaction between two concentric cylinders at nonzero temperature
We study the finite temperature Casimir interaction between two concentric
cylinders. When the separation between the cylinders is much smaller than the
radii of the cylinders, the asymptotic expansions of the Casimir interaction
are derived. Both the low temperature and the high temperature regions are
considered. The leading terms are found to agree with the proximity force
approximations. The low temperature leading term of the temperature correction
is also computed and it is found to be independent of the boundary conditions
imposed on the larger cylinder.Comment: 6 pages, 1 figur
Dynamical Casimir effect in superconducting circuits: a numerical approach
We present a numerical analysis of the particle creation for a quantum field
in the presence of time dependent boundary conditions. Having in mind recent
experiments involving superconducting circuits, we consider their description
in terms of a scalar field in a one dimensional cavity satisfying generalized
boundary conditions that involve a time-dependent linear combination of the
field and its spatial and time derivatives. We evaluate numerically the
Bogoliubov transformation between {\it in} and {\it out}-states and find that
the rate of particle production strongly depends on whether the spectrum of the
unperturbed cavity is equidistant or not, and also on the amplitude of the
temporal oscillations of the boundary conditions. We provide analytic
justifications for the different regimes found numerically.Comment: 20 pages. 11 figure
Cosmological Magnetic Fields from Gauge-Mediated Supersymmetry-Breaking Models
We study the generation of primordial magnetic fields, coherent over
cosmologically interesting scales, by gravitational creation of charged scalar
particles during the reheating period. We show that magnetic fields consistent
with those detected by observation may obtained if the particle mean life
\tau_s is in the range 10^{-14} sec \leq \tau_s \leq 10{-7} sec. We apply this
mechanism to minimal gauge mediated supersymmetry-breaking models, in the case
in which the lightest stau \tilde\tau_1 is the next-to-lightest supersymmetric
particle. We show that, for a large range of phenomenologically acceptable
values of the supersymmetry-breaking scale \sqrt{F}, the generated primordial
magnetic field can be strong enough to seed the galactic dynamo.Comment: 12 pages, Latex. Final version accepted for publication in Phys.
Lett.
Casimir force between eccentric cylinders
We consider the Casimir interaction between a cylinder and a hollow cylinder,
both conducting, with parallel axis and slightly different radii. The Casimir
force, which vanishes in the coaxial situation, is evaluated for both small and
large eccentricities using the proximity approximation. The cylindrical
configuration offers various experimental advantages with respect to the
parallel planes or the plane-sphere geometries, leading to favourable
conditions for the search of extra-gravitational forces in the micrometer range
and for the observation of finite temperature corrections.Comment: To be published in Europhysics Letters. 7 pages, 4 figure
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