Umut Gursoy

Thermal Transport and Drag Force in Improved Holographic QCD

We calculate the bulk viscosity, drag force and jet quenching parameter in Improved Holographic QCD. We find that the bulk viscosity rises near the phase transition but does not exceed the shear viscosity. The drag force shows the effects of asymptotic freedom both as a function of velocity and temperature. It indicates diffusion times of heavy quarks in rough agreement with data. The jet quenching parameter values computed via the light-like Wilson loop are in the lower range suggested by data.

Holography and thermodynamics of 5D dilaton-gravity

The asymptotically-logarithmically-AdS black-hole solutions of 5D dilaton gravity with a monotonic dilaton potential are analyzed in detail. Such theories are holographically very close to pure Yang-Mills theory in four dimensions. The existence and uniqueness of black-hole solutions is shown. It is also shown that a Hawking-Page transition exists at finite temperature if and only if the potential corresponds to a confining theory. The physics of the transition matches in detail with that of deconfinement of the Yang-Mills theory. The high-temperature phase asymptotes to a free gluon gas at high temperature matching the expected behavior from asymptotic freedom. The thermal gluon condensate is calculated and shown to be crucial for the existence of a non-trivial deconfining transition. The condensate of the topological charge is shown to vanish in the deconfined phase.

Improved holographic Yang–Mills at finite temperature: comparison with data

Abstract The semi-phenomenological improved holographic model for QCD is confronted with data of the pure glue, large- N c gauge theory. After fitting two phenomenological parameters in the potential, the model can reproduce in detail all thermodynamic functions at finite temperature. It also reproduces in detail all known spin-0 and spin-2 glueball observables at zero temperature and predicts the rest of the 0 + + and 2 + + towers. A similar two parameter fit in the CP-odd sector postdicts the correct second 0 + − glueball mass, and predicts the rest of the 0 + − tower.

Improved Holographic QCD

We provide a review to holographic models based on Einstein-dilaton gravity with a potential in five dimensions. Such theories, for a judicious choice of potential are very close to the physics of large-N YM theory both at zero and finite temperature. The zero temperature glueball spectra as well as their finite temperature thermodynamic functions compare well with lattice data. The model can be used to calculate transport coefficients, like bulk viscosity, the drag force and jet quenching parameters, relevant for the physics of the Quark–Gluon Plasma.

RG flows from spin(7), CY 4 fold and HK manifolds to AdS, Penrose limits and pp waves

We obtain explicit realizations of holographic renormalization group (RG) flows from M-theory, from E2,1 × Spin(7) at UV to AdS4 × 7 (squashed S7) at IR, from E2,1 × CY4 at UV to AdS4 × Q1,1,1 at IR, and from E2,1 × HK (hyperKahler) at UV to AdS4 × N0,1,0 at IR. The dual type-IIA string theory configurations correspond to D2-D6 brane systems where D6-branes wrap supersymmetric four-cycles. We also study the Penrose limits and obtain the pp-wave backgrounds for the above configurations. Besides, we study some examples of non-supersymmetric and supersymmetric flows in five-dimensional gauge theories.

Dipole deformations of N=1 SYM and supergravity backgrounds with U(1)×U(1) global symmetry

We study SL(3,R) deformations of a type IIB background based on D5 branes that is conjectured to be dual to N=1 SYM. We argue that this deformation of the geometry correspond to turning on a dipole deformation in the field theory on the D5 branes. We give evidence that this deformation only affects the KK-sector of the dual field theory and helps decoupling the KK dynamics from the pure gauge dynamics. Similar deformations of the geometry that is dual to N=2 SYM are studied. Finally, we also study a deformation that leaves us with a possible candidate for a dual to N=0 YM theory.

Vector operators in the BMN correspondence

We consider a BMN operator with one scalar, and one vector, DμZ, impurity field and compute the anomalous dimension both at planar and torus levels. This mixed operator corresponds to a string state with two creation operators which belong to different SO(4) sectors of the background. The anomalous dimension at both levels is found to be the same as the scalar impurity BMN operator. At planar level this constitutes a consistency check of BMN conjecture. Agreement at the torus level can be explained by an argument using supersymmetry and supression in the BMN limit. The same argument implies that a class of fermionic BMN operators also have the same planar and torus level anomalous dimensions. Implications of the results for the map from = 4 SYM theory to string theory in the pp-wave background are discussed.We consider a BMN operator with one scalar, φ and one vector, DμZ, impurity field and compute the anomalous dimension both at planar and torus levels. This mixed operator corresponds to a string state with two creation operators which belong to different SO(4) sectors of the background. The anomalous dimension at both levels is found to be the same as the scalar impurity BMN operator. At planar level this constitutes a consistency check of BMN conjecture. Agreement at the torus level can be explained by an argument using supersymmetry and supression in the BMN limit. The same argument implies that a class of fermionic BMN operators also have the same planar and torus level anomalous dimensions. Implications of the results for the map from N = 4 SYM theory to string theory in the pp-wave background are discussed.

Dipole deformations of N=1 SYM and supergravity backgrounds with U(1) x U(1) global symmetry

We study SL(3,R) deformations of a type IIB background based on D5 branes that is conjectured to be dual to N=1 SYM. We argue that this deformation of the geometry correspond to turning on a dipole deformation in the field theory on the D5 branes. We give evidence that this deformation only affects the KK-sector of the dual field theory and helps decoupling the KK dynamics from the pure gauge dynamics. Similar deformations of the geometry that is dual to N=2 SYM are studied. Finally, we also study a deformation that leaves us with a possible candidate for a dual to N=0 YM theory.

Magnetohydrodynamics, charged currents, and directed flow in heavy ion collisions

The hot QCD matter produced in any heavy ion collision with a nonzero impact parameter is produced within a strong magnetic field. We study the imprint that these fields leave on the azimuthal distributions and correlations of the produced charged hadrons. The magnetic field is time-dependent and the medium is expanding, which leads to the induction of charged currents due to the combination of Faraday and Hall effects. We find that these currents result in a charge- dependent directed flow v1 that is odd in rapidity and odd under charge exchange. It can be detected by measuring correlations between the directed flow of charged hadrons at different rapidities,

Comments on the beta-deformed N=4 SYM Theory

\langle v_1^\pm(y_1)v_1^\pm(y_2)\rangle