533 research outputs found
Differential cross section analysis in kaon photoproduction using associated legendre polynomials
Angular distributions of differential cross sections from the latest CLAS
data sets \cite{bradford}, for the reaction have been analyzed using associated Legendre polynomials. This
analysis is based upon theoretical calculations in Ref. \cite{fasano} where all
sixteen observables in kaon photoproduction can be classified into four
Legendre classes. Each observable can be described by an expansion of
associated Legendre polynomial functions. One of the questions to be addressed
is how many associated Legendre polynomials are required to describe the data.
In this preliminary analysis, we used data models with different numbers of
associated Legendre polynomials. We then compared these models by calculating
posterior probabilities of the models. We found that the CLAS data set needs no
more than four associated Legendre polynomials to describe the differential
cross section data. In addition, we also show the extracted coefficients of the
best model.Comment: Talk given at APFB08, Depok, Indonesia, August, 19-23, 200
Exclusive electromagnetic production of strangeness on the nucleon : review of recent data in a Regge approach
In view of the numerous experimental results recently released, we provide in
this letter an update on the performance of our simple Regge model for
strangeness electroproduction on the nucleon. Without refitting any parameters,
a decent description of all measured observables and channels is achieved. We
also give predictions for spin transfer observables, recently measured at
Jefferson Lab which have high sensitivity to discriminate between different
theoretical approaches.Comment: 5 pages, 5 figure
Benchmarking nuclear models for Gamow-Teller response
A comparative study of the nuclear Gamow-Teller response (GTR) within
conceptually different state-of-the-art approaches is presented. Three nuclear
microscopic models are considered: (i) the recently developed charge-exchange
relativistic time blocking approximation (RTBA) based on the covariant density
functional theory, (ii) the shell model (SM) with an extended "jj77" model
space and (iii) the non-relativistic quasiparticle random-phase approximation
(QRPA) with a Brueckner G-matrix effective interaction. We study the physics
cases where two or all three of these models can be applied. The Gamow-Teller
response functions are calculated for 208-Pb, 132-Sn and 78-Ni within both RTBA
and QRPA. The strengths obtained for 208-Pb are compared to data that enables a
firm model benchmarking. For the nucleus 132-Sn, also SM calculations are
performed within the model space truncated at the level of a particle-hole (ph)
coupled to vibration configurations. This allows a consistent comparison to the
RTBA where ph+phonon coupling is responsible for the spreading width and
considerable quenching of the GTR. Differences between the models and
perspectives of their future developments are discussed.Comment: 9 pages, 2 figures, 1 table; to be published in Phys. Lett.
Simple compactifications and Black p-branes in Gauss-Bonnet and Lovelock Theories
We look for the existence of asymptotically flat simple compactifications of
the form in -dimensional gravity theories with higher
powers of the curvature. Assuming the manifold to be spherically
symmetric, it is shown that the Einstein-Gauss-Bonnet theory admits this class
of solutions only for the pure Einstein-Hilbert or Gauss-Bonnet Lagrangians,
but not for an arbitrary linear combination of them. Once these special cases
have been selected, the requirement of spherical symmetry is no longer relevant
since actually any solution of the pure Einstein or pure Gauss-Bonnet theories
can then be toroidally extended to higher dimensions. Depending on and the
spacetime dimension, the metric on may describe a black hole or a
spacetime with a conical singularity, so that the whole spacetime describes a
black or a cosmic -brane, respectively. For the purely Gauss-Bonnet theory
it is shown that, if is four-dimensional, a new exotic class of black
hole solutions exists, for which spherical symmetry can be relaxed.
Under the same assumptions, it is also shown that simple compactifications
acquire a similar structure for a wide class of theories among the Lovelock
family which accepts this toroidal extension.
The thermodynamics of black -branes is also discussed, and it is shown
that a thermodynamical analogue of the Gregory-Laflamme transition always
occurs regardless the spacetime dimension or the theory considered, hence not
only for General Relativity.
Relaxing the asymptotically flat behavior, it is also shown that exact black
brane solutions exist within a very special class of Lovelock theories.Comment: 30 pages, no figures, few typos fixed, references added, final
version for JHE
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