More on supersymmetric tensionless rotating strings in AdS_5 x S^5

Rotating IIB strings in AdS_5 x S^5 become ultra-relativistic, and hence effectively tensionless, in the limit of large angular momentum on S^5. We have shown previously that such tensionless strings may preserve supersymmetry. Here we extend this result to include a class of supersymmetric tensionless strings with arbitrary SO(6) angular momentum. We close with some general comments on tensionless strings in AdS_5 x S^5.Comment: Contribution to the 3rd International Symposium on Quantum Theory and Symmetries (QTS3), Cincinnati, 10-14 Sep 200

Bright branes for strongly coupled plasmas

We use holographic techniques to study photon production in a class of finite temperature, strongly coupled, large-Nc SU(Nc) quark-gluon plasmas with Nf << Nc quark flavours. Our results are valid to leading order in the electromagnetic coupling constant but non-perturbatively in the SU(Nc) interactions. The spectral function of electromagnetic currents and other related observables exhibit an interesting structure as a function of the photon frequency and the quark mass. We discuss possible implications for heavy ion collision experiments.Comment: 29 pages, 14 figure

Prediction of a Photon Peak in Heavy Ion Collisions

We show that if a flavour-less vector meson remains bound after deconfinement, and if its limiting velocity in the quark-gluon plasma is subluminal, then this meson produces a distinct peak in the spectrum of thermal photons emitted by the plasma. We also demonstrate that this effect is a universal property of all strongly coupled, large-Nc plasmas with a gravity dual. For the J/psi the corresponding peak lies between 3 and 5 GeV and could be observed at LHC.Comment: 4 pages, 5 figures. Minor corrections; references adde

Quarks, gluons i forats negres

El 18 d'abril del 2005 a Tampa, Florida (Estats Units), es va anunciar que un nou estat de matèria, anomenat plasma de quarks i gluons (PQG, en anglès), havia estat creat en col.lisions d'ions pesants al Relativistic Heavy Ion Collider (RHIC) de Brookhaven, a Nova York. Algunes de les propietats del plasma de quarks i gluons (PQG, d'ara endavant), com per exemple la seva petita viscositat, són extremament sorprenents tant per si mateixes com pel fet que semblen estar relacionades amb propietats de forats negres en teoria de cordes, una teoria que unifica totes les forces de la natura, incloent-hi la força gravitatòria. De fet, l'anunci anterior va ser el primer anunci dels resultats d'un experiment de gran magnitud en què es va esmentar la teoria de cordes. Des d'aleshores s'ha produït una explosió d'activitat en el desenvolupament de la connexió entre la física del PQG i la de forats negres. L'objectiu d'aquest article és explicar aquesta connexió i les seves conseqüències i aplicacions potencials

Supercurves

The TST-dual of the general 1/4-supersymmetric D2-brane supertube is identified as a 1/4-supersymmetric IIA `supercurve': a string with arbitrary transverse displacement travelling at the speed of light. A simple proof is given of the classical upper bound on the angular momentum, which is also recovered as the semi-classical limit of a quantum bound. The classical bound is saturated by a `superhelix', while the quantum bound is saturated by a bosonic oscillator state in a unique SO(8) representation.Comment: 1+14 pages, LaTe

Off-diagonal Flavour Susceptibilities from AdS/CFT

We study flavour susceptibilities in the ${\cal N}=4$ SU(N) super Yang-Mills plasma coupled to two quark flavours at strong coupling and large $N$ by means of its gravity dual. The off-diagonal susceptibility is 1/N-suppressed and we compute it as a one-loop effect on the gravity side. Contrary to naive extrapolation from perturbative results, it attains a finite value in the infinite-coupling limit. Moreover, its parametric form is independent of whether or not meson bound states exist in the plasma. We conclude that caution must be exercised when drawing conclusions about the QCD plasma from lattice calculations of quark susceptibilities.Comment: 4 page