A Proposal for Altering the Unification Scale in String Theory

An ensemble of short open strings in equilibrium with the heat bath provided by the Euclidean worldvolume of a stack of Dbranes undergoes a thermal phase transition to a long string phase. The transition temperature is just below the string scale. We point out that this phenomenon provides a simple mechanism within open and closed string theories for altering the strong-electro-weak coupling unification scale relative to the fundamental closed string mass scale in spacetimes with external electromagnetic background.Comment: Latex, 7pgs. v5 Minor changes to main paper. Note added, following recent clarification of the first-order deconfining phase transition to a long string phase in the low energy finite temperature supersymmetric gauge theory limit (hep-th/0409301). Updated references. v6 Eq2 correcte

Transverse energy dependence of J/Psi suppression in Au+Au collisions at RHIC energy

Prediction for transverse energy dependence of $J/\psi$ to Drell-Yan ratio in Au+Au collisions at RHIC energy was obtained in a model which assume 100% absorption of $J/\psi$ above a threshold density. The threshold density was obtained by fitting the NA50 data on $J/\psi$ suppression in Pb+Pb collisions at SPS energy. At RHIC energy, hard processes may be important. Prediction of $J/\psi$ suppression with and without hard processes were obtained. With hard processes included, $J/\psi$'s are strongly suppressed.Comment: 4 pages, 2 figures (revised version

Charged particle's elliptic flow in 2+1D viscous hydrodynamics at LHC (s\sqrt{s}= 2.76 TeV) energy in Pb+Pb collision

In the Israel-Stewart's theory of second order hydrodynamics, we have simulated $\sqrt{s}$=2.76 TeV Pb+Pb collisions. ALICE data for the centrality dependence of charged particles multiplicity, $p_T$ spectra in 0-5% collisions, centrality dependence of integrated and differential elliptic flow are analysed. Analysis indicate that while ALICE data on charged particles multiplicity or $p_T$ spectra do not demand any viscosity, viscosity is demanded by the elliptic flow data. From a simulataneous fit to all the data sets, viscosity to entropy ratio in $\sqrt{s}_{NN}$=2.76 TeV Pb+Pb collisions is extracted as, $\eta/s=0.06\pm 0.02$.Comment: Significantly revised version. New figures are added. Accepted in Phys. Lett. B. 6 pages, 6 figure

Spacetime Reduction of Large N Flavor Models: A Fundamental Theory of Emergent Local Geometry?

We introduce a novel spacetime reduction procedure for the fields of a supergravity-Yang-Mills theory in generic curved spacetime background, and with large N flavor group, to linearized forms on an infinitesimal patch of local tangent space at a point in the spacetime manifold. Our new prescription for spacetime reduction preserves all of the local symmetries of the continuum field theory Lagrangian in the resulting zero-dimensional matrix Lagrangian, thereby obviating difficulties encountered in previous matrix proposals for emergent spacetime in recovering the full nonlinear symmetries of Einstein gravity. We conjecture that the zero-dimensional matrix model obtained by this prescription for spacetime reduction of the circle-compactified type I-I'-mIIA-IIB-heterotic supergravity-Yang-Mills theory with sixteen supercharges and large N flavor group, and inclusive of the full spectrum of Dpbrane charges, offers a potentially complete framework for nonperturbative string/M theory. We explain the relationship of our conjecture for a fundamental theory of emergent local spacetime geometry to recent investigations of the hidden symmetry algebra of M theory, stressing insights that are to be gained from the algebraic perspective. We conclude with a list of open questions and directions for future work.Comment: 30pgs. v6: Ref [4] added, some terminology corrected in Intro, sections 5,6. Footnote 2 clarifies the relation to hep-th/0201129v1. Acknowledgments adde