693 research outputs found

    Generalized Emission Functions for Photon Emission from Quark-Gluon Plasma

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    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 (f~(p~‚ä•){\bf \tilde{f}(\tilde{p}_\perp)}) and the longitudinal function (g~(p~‚ä•)\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 \{p0,q0,Q2p_0,q_0,Q^2\}, considering the bremsstrahlung and the aws\bf aws processes. We define four new dynamical scaling variables, xTbx^b_T,xTax^a_T,xLbx^b_L,xLax^a_L for bremsstrahlung and {\bf aws} processes and analyse the transverse and longitudinal components as a function of \{p0,q0,Q2p_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 gTbg^b_T, gTag^a_T, gLbg^b_L, gLag^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 gT,Lb,ag^{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

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    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

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    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

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    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 (r0_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 ¬Ī8\pm 8% deviation to data, showing the scope for improvement. It has been observed that a finer adjustment of r0_0 parameter alone can give very good Ramsauer model description of neutron total scattering data within ¬Ī4\pm 4% deviation. The required r0_0 values for Ramsauer model fits are shown as a function of nuclear mass number and an empirical formula is suggested for r0_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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