Dimitrios Zoakos

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.

Holographic flavor in = 4 gauge theories in 3d from wrapped branes

We study the addition of flavor to the gravity dual of = 4 three-dimensional gauge theories obtained by wrapping Nc D4-branes on a two-cycle of a non-compact Calabi-Yau two-fold. In this setup the flavor is introduced by adding another set of D4-branes that are extended along the non-compact directions of the Calabi-Yau which are normal to the cycle which the color branes wrap. The analysis is performed both in the quenched and unquenched approximations. In this latter case we compute the backreacted metric and we show that it reproduces the running of the gauge coupling. The meson spectrum and the behavior of Wilson loops are also discussed and the holographic realization of the Higgs branch is analyzed. Other aspects of this system studied are the entanglement entropy and the non-relativistic version of our backgrounds.

Gravity duals for the Coulomb branch of marginally deformed N=4 Yang-Mills

Supergravity backgrounds dual to a class of exactly marginal deformations of N = 4 supersymmetric Yang–Mills can be constructed through an SL(2, R) sequence of T-dualities and coordinate shifts. We apply this transformation to multicenter solutions and derive supergravity backgrounds describing the Coulomb branch of N = 1 theories at strong ’t Hooft coupling as marginal deformations of N = 4 Yang–Mills. For concreteness we concentrate to cases with an SO(4) ×SO(2) symmetry preserved by continuous distributions of D3-branes on a disc and on a three-dimensional spherical shell. We compute the expectation value of the Wilson loop operator and confirm the Coulombic behaviour of the heavy quark-antiquark potential in the conformal case. When the vev is turned on we find situations where a complete screening of the potential arises, as well as a confining regime where a linear or a logarithmic potential prevails depending on the ratio of the quark-antiquark separation to the typical vev scale. The spectra of massless excitations on these backgrounds are analyzed by turning the associated differential equations into Schr¨odinger problems. We find explicit solutions taking into account the entire tower of states related to the reduction of type-IIB supergravity to five dimensions, and hence we go beyond the s-wave approximation that has been considered before for the undeformed case. Arbitrary values of the deformation parameter give rise to the Heun differential equation and the related Inozemtsev integrable system, via a non-standard trigonometric limit as we explicitly demonstrate.

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.

Supersymmetric solutions based on Y^{p,q} and L^{p,q,r}

Abstract We explicitly realize supersymmetric cones based on the five-dimensional Y p , q and L p , q , r Einstein–Sasaki spaces. We use them to construct supersymmetric type IIB supergravity solutions representing a stack of D3- and D5-branes as warped products of the six-dimensional cones and R 1 , 3 .

Supersymmetry and Lorentzian holonomy in various dimensions

We present a systematic method for constructing manifolds with Lorentzian holonomy group that are non-static supersymmetric vacua admitting covariantly constant light-like spinors. It is based on the metric of their Riemannian counterparts and the realization that, when certain conditions are satisfied, it is possible to promote constant moduli parameters into arbitrary functions of the light-cone time. Besides the general formalism, we present in detail several examples in various dimensions.

Supersymmetric solutions based on Yp,q and Lp,q,r

Abstract We explicitly realize supersymmetric cones based on the five-dimensional Y p , q and L p , q , r Einstein–Sasaki spaces. We use them to construct supersymmetric type IIB supergravity solutions representing a stack of D3- and D5-branes as warped products of the six-dimensional cones and R 1 , 3 .

On supersymmetry and other properties of a class of marginally deformed backgrounds

We summarize our recent work on supergravity backgrounds dual to part of the Coulomb branch of N = 1 theories constructed as marginal deformations of N = 4 Yang–Mills. In particular, we present a summary of the behaviour of the heavy quark-antiquark potential which shows confining behaviour in the IR as well as of the spectrum of the wave equation. The reduced supersymmetry is due to the implementation of T-duality in the construction of the deformed supergravity solutions. As a new result we analyze and explicitly solve the Killing spinor equations of the N = 1 background in the superconformal limit.

Entanglement Entropy of the N=4 SYM spin chain

A bstractWe present a detailed study of the Entanglement Entropy (EE) of excited states in all closed rank one subsectors of N=4