743 research outputs found
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
Euclidean Scalar Green Function in a Higher Dimensional Global Spacetime
We construct the explicit Euclidean scalar Green function associated with a
massless field in a higher dimensional global monopole spacetime, i.e., a
-spacetime with which presents a solid angle deficit. Our
result is expressed in terms of a infinite sum of products of Legendre
functions with Gegenbauer polynomials. Although this Green function cannot be
expressed in a closed form, for the specific case where the solid angle deficit
is very small, it is possible to develop the sum and obtain the Green function
in a more workable expression. Having this expression it is possible to
calculate the vacuum expectation value of some relevant operators. As an
application of this formalism, we calculate the renormalized vacuum expectation
value of the square of the scalar field, , and the
energy-momentum tensor, , for the global monopole
spacetime with spatial dimensions and .Comment: 18 pages, LaTex format, no figure
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
A complete O(alpha_S^2) calculation of the signal-background interference for the Higgs diphoton decay channel
We present the full {\cal O}(\as^2) computation of the interference effects
between the Higgs diphoton signal and the continuum background at the LHC.
While the main contribution to the interference originates on the partonic
subprocess, we find that the corrections from the and channels
amount up to 35% of it. We discuss the effect of these new subprocesses in the
shift of the diphoton invariant mass peak recently reported by S. Martin in
Ref.\cite{Martin:2012xc}.Comment: 8 pages, 5 figure
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
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