Spyros D. Avramis

Supergravity and the jet quenching parameter in the presence of R-charge densities

Following a recent proposal, we employ the AdS/CFT correspondence to compute the jet quenching parameter for = 4 Yang-Mills theory at nonzero R-charge densities. Using as dual supergravity backgrounds non-extremal rotating branes, we find that the presence of the R-charges generically enhances the jet quenching phenomenon. However, at fixed temperature, this enhancement might or might not be a monotonically increasing function of the R-charge density and depends on the number of independent angular momenta describing the solution. We perform our analysis for the canonical as well as for the grand canonical ensemble which give qualitatively similar results.

On the velocity and chemical-potential dependence of the heavy-quark interaction in N=4 SYM plasmas

We consider the interaction of a heavy quark-antiquark pair moving in N=4 SYM plasma in the presence of non-vanishing chemical potentials. Of particular importance is the maximal length beyond which the interaction is practically turned off. We propose a simple phenomenological law that takes into account the velocity dependence of this screening length beyond the leading order and in addition its dependence on the R-charge. Our proposal is based on studies using rotating D3-branes.

Stability of strings dual to flux tubes between static quarks in N=4 SYM

Abstract Computing heavy quark–antiquark potentials within the AdS/CFT correspondence often leads to behaviors that differ from what one expects on general physical grounds and field-theory considerations. To isolate the configurations of physical interest, it is of utmost importance to examine the stability of the string solutions dual to the flux tubes between the quark and antiquark. Here, we formulate and prove several general statements concerning the perturbative stability of such string solutions, relevant for static quark–antiquark pairs in a general class of backgrounds, and we apply the results to N = 4 SYM at finite temperature and at generic points of the Coulomb branch. In all cases, the problematic regions are found to be unstable and hence physically irrelevant.

A systematic search for anomaly-free supergravities in six dimensions

We conduct a systematic search for anomaly-free six-dimensional = 1 chiral supergravity theories. Under a certain set of restrictions on the allowed gauge groups and the representations of the hypermultiplets, we enumerate all possible Poincare and gauged supergravities with one tensor multiplet satisfying the 6D anomaly cancellation criteria.

Stability of string configurations dual to quarkonium states in AdS/CFT

Abstract We extend our earlier work, regarding the perturbative stability of string configurations used for computing the interaction potential of heavy quarks within the gauge/gravity correspondence, to cover a more general class of gravity duals. We provide results, mostly based on analytic methods and corroborated by numerical calculations, which apply to strings in a general class of backgrounds that encompass boosted, spinning and marginally-deformed D3-brane backgrounds. For the case of spinning branes we demonstrate in a few examples that perturbative stability of strings may require strong conditions complementing those following by thermodynamic stability of the dual field theories. For marginally-deformed backgrounds, we find that even in the conformal case stability requires an upper value for the imaginary part σ of the deformation parameter, whereas in regions of the Coulomb branch where there exists linear confinement we find that there exist stable string configurations for certain ranges of values of the parameter σ . We finally discuss the case of open strings with fixed endpoints propagating in Rindler space, which turns out to have an exact classical-mechanical analog.

A NEW ANOMALY-FREE GAUGED SUPERGRAVITY IN SIX DIMENSIONS

We present a new anomaly-free gauged = 1 supergravity model in six dimensions. The gauge group is E7 × G2 × U(1)R, with all hyperinos transforming in the product representation (56,14). The theory admits monopole compactifications to 4 × S2, leading to D = 4 effective theories with broken supersymmetry and massless fermions.

Complex marginal deformations of D3-brane geometries, their Penrose limits and giant gravitons

We apply the Lunin--Maldacena construction of gravity duals to beta-deformed gauge theories to a class of Type IIB backgrounds with U(1)^3 global symmetry, which include the multicenter D3-brane backgrounds dual to the Coulomb branch of N=4 super Yang-Mills and the rotating D3-brane backgrounds dual to the theory at finite temperature and chemical potential. After a general discussion, we present the full form of the deformed metrics for three special cases, which can be used for the study of various aspects of the marginally-deformed gauge theories. We also construct the Penrose limits of the solutions dual to the Coulomb branch along a certain set of geodesics and, for the resulting PP--wave metrics, we examine the effect of beta-deformations on the giant graviton states. We find that giant gravitons exist only up to a critical value of the sigma-deformation parameter, are not degenerate in energy with the point graviton, and remain perturbatively stable. Finally, we probe the sigma-deformed multicenter solutions by examining the static heavy-quark potential by means of Wilson loops. We find situations that give rise to complete screening as well as linear confinement, with the latter arising is an intriguing way reminiscent of phase transitions in statistical systems.

Gauged D = 7 supergravity on the S**1 / Z(2)orbifold

We construct the most general couplings of a bulk seven-dimensional Yang-Mills-Einstein

Three-dimensional AdS gravity and extremal CFTs at c = 8m

\mathcal{N}=2

Gauged D=7 supergravity on the S{sup 1}/Z{sub 2} orbifold

supergravity with a boundary six-dimensional chiral