8,323 research outputs found
Spinning AdS Propagators
We develop the embedding formalism to describe symmetric traceless tensors in
Anti-de Sitter space. We use this formalism to construct the bulk-to-bulk
propagator of massive spin J fields and check that it has the expected short
distance and massless limits. We also and a split representation for the
bulk-to-bulk propagator, by writing it as an integral over the boundary of the
product of two bulk-to-boundary propagators. We exemplify the use of this
representation with the computation of the conformal partial wave decomposition
of Witten diagrams. In particular, we determine the Mellin amplitude associated
to AdS graviton exchange between minimally coupled scalars of general
dimension, including the regular part of the amplitude.Comment: 48 pages, 6 figure
Scalar perturbations and the possible self-destruction of the phantom menace
Some analysis of the supernovae type Ia observational data seems to indicate
that the Universe today is dominated by a phantom field, for which all energy
conditions are violated. Such phantom field may imply a singularity in a future
finite time, called big rip. Studying the evolution of scalar perturbations for
such a field, we show that if the pressure is negative enough, the Universe can
become highly inhomogeneous and this phantom menace may be avoided.Comment: Latex file, 5 page
Does magnetic pressure affect the ICM dynamics?
A possible discrepancy found in the determination of mass from gravitational
lensing data, and from X-rays observations, has been largely discussed in the
latest years (for instance, Miralda-Escude & Babul (1995)). Another important
discrepancy related to these data is that the dark matter is more centrally
condensed than the X-ray-emitting gas, and also with respect to the galaxy
distribution (Eyles et al. 1991). Could these discrepancies be consequence of
the standard description of the ICM, in which it is assumed hydrostatic
equilibrium maintained by thermal pressure? We follow the evolution of the ICM,
considering a term of magnetic pressure, aiming at answering the question
whether or not these discrepancies can be explained via non-thermal terms of
pressure. Our results suggest that the magnetic pressure could only affect the
dynamics of the ICM on scales as small as < 1kpc. Our models are constrained by
the observations of large and small scale fields and we are successful at
reproducing available data, for both Faraday rotation limits and inverse
Compton limits for the magnetic fields. In our calculations the radius (from
the cluster center) in which magnetic pressure reaches equipartition is smaller
than radii derived in previous works, as a consequence of the more realistic
treatment of the magnetic field geometry and the consideration of a sink term
in the cooling flow.Comment: 8 pages with 7 figures included. MNRAS accepted. Minor changes in the
section of discussions and conclusions. Also available at
http://www.iac.es/publicaciones/preprints.htm
Bottom production in Photon and Pomeron -- induced interactions at the LHC
In this paper we present a detailed comparison of the bottom production in
gluon -- gluon, photon -- gluon, photon -- photon, pomeron -- gluon, pomeron --
pomeron and pomeron -- photon interactions at the LHC. The transverse momentum,
pseudo -- rapidity and dependencies of the cross sections are calculated
at LHC energy using the Forward Physics Monte Carlo (FPMC), which allows to
obtain realistic predictions for the bottom production with one or two leading
intact protons. Moreover, predictions for the the kinematical range probed by
the LHCb Collaboration are also presented. Our results indicate that the
analysis of the single diffractive events is feasible using the Run I LHCb
data.Comment: 8 pages, 3 figures, 1 table. Version published in Physical Review
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