693 research outputs found

### Generalized Emission Functions for Photon Emission from Quark-Gluon Plasma

The Landau-Pomeranchuk-Migdal effects on photon emission from the quark gluon
plasma have been studied as a function of photon mass, at a fixed temperature
of the plasma. The integral equations for the transverse vector function (${\bf
\tilde{f}(\tilde{p}_\perp)}$) and the longitudinal function ($\tilde{g}({\bf
\tilde{p}_\perp})$) consisting of multiple scattering effects are solved by the
self consistent iterations method and also by the variational method for the
variable set \{$p_0,q_0,Q^2$\}, considering the bremsstrahlung and the $\bf
aws$ processes. We define four new dynamical scaling variables,
$x^b_T$,$x^a_T$,$x^b_L$,$x^a_L$ for bremsstrahlung and {\bf aws} processes and
analyse the transverse and longitudinal components as a function of
\{$p_0,q_0,Q^2$\}. We generalize the concept of photon emission function and we
define four new emission functions for massive photon emission represented by
$g^b_T$, $g^a_T$, $g^b_L$, $g^a_L$. These have been constructed using the exact
numerical solutions of the integral equations. These four emission functions
have been parameterized by suitable simple empirical fits. In terms of these
empirical emission functions, the virtual photon emission from quark gluon
plasma reduces to one dimensional integrals that involve folding over the
empirical $g^{b,a}_{T,L}$ functions with appropriate quark distribution
functions and the kinematic factors. Using this empirical emission functions,
we calculated the imaginary part of the photon polarization tensor as a
function of photon mass and energy.Comment: In nuclear physics journals and arxiv listings, my name used to
appear as S.V.S. Sastry. Hereafter, my name will appear as, S.V.
Suryanarayan

### A Stable Non-BPS Configuration From Intersecting Branes and Antibranes

We describe a tachyon-free stable non-BPS brane configuration in type IIA string theory. The configuration is an elliptic model involving rotated NS5 branes, D4 branes and anti-D4 branes, and is dual to a fractional brane-antibrane pair placed at a conifold singularity. This configuration exhibits an interesting behaviour as we vary the radius of the compact direction. Below a critical radius the D4 and anti-D4 branes are aligned, but as the radius increases above the critical value the potential between them develops a minimum away from zero. This signals a phase transition to a configuration with finitely separated branes

### Stable Non-BPS States and Their Holographic Duals

Stable non-BPS states can be constructed and studied in a variety of contexts
in string theory. Here we review some interesting constructions that arise from
suspended and wrapped branes. We also exhibit some stable non-BPS states that
have holographic duals.Comment: 10 pages, LaTeX, 10 .eps figures (included); based on a talk given at
Strings 2000, Michiga

### Total cross sections for neutron-nucleus scattering

Systematics of neutron scattering cross sections on various materials for
neutron energies up to several hundred MeV are important for ADSS applications.
Ramsauer model is well known and widely applied to understand systematics of
neutron nucleus total cross sections. In this work, we examined the role of
nuclear effective radius parameter (r$_0$) on Ramsauer model fits of neutron
total cross sections. We performed Ramsauer model global analysis of the
experimental neutron total cross sections reported by W. P. Abfalterer, F. B.
Bateman, {\it et. al.,}, from 20MeV to 550MeV for nuclei ranging from Be to U .
The global fit functions which can fit total cross section data over periodic
table are provided along with the required global set of parameters. The global
fits predict within $\pm 8%$ deviation to data, showing the scope for
improvement. It has been observed that a finer adjustment of r$_0$ parameter
alone can give very good Ramsauer model description of neutron total scattering
data within $\pm 4%$ deviation. The required r$_0$ values for Ramsauer model
fits are shown as a function of nuclear mass number and an empirical formula is
suggested for r$_0$ values as a function of mass number. In optical model
approach for neutron scattering, we have modified the real part of
Koning-Deleroche potentails to fit the neutron total cross sections using SCAT2
code. The modified potentails have a different energy dependence beyond 200MeV
of neutron energy and fit the total cross sections from Al to Pb.Comment: 9 pages, 20figures, Poster number ND-1457, ND2010 Conference in Kore

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