arXiv subjects

Javier Mas

Publications and source records attributed to Javier Mas.

At least 37 records · Page 2Linked to original sources

arXiv2014

Holographic Relaxation of Finite Size Isolated Quantum Systems

We study holographically the out of equilibrium dynamics of a finite size closed quantum system in 2+1 dimensions, modelled by the collapse of a shell of a massless scalar field in AdS4. In global coordinates there exists a variety of evolutions towards final black hole formation which we relate with different patterns of relaxation in the dual field theory. For large scalar initial data rapid thermalization is achieved as a priori expected. Interesting phenomena appear for small enough amplitudes. Such shells do not generate a black hole by direct collapse, but quite generically an apparent horizon emerges after enough bounces off the AdS boundary. We relate this bulk evolution with relaxation processes at strong coupling which delay in reaching an ergodic stage. Besides the dynamics of bulk fields, we monitor the entanglement entropy, finding that it oscillates quasi-periodically before final equilibration. The radial position of the traveling shell is brought into correspondence with the evolution of the entanglement pattern in the dual field theory. The entanglement entropy is not only able to portrait the streaming of entangled excitations, but it is also a useful probe of interaction effects.

hep-th↗

arXiv2012

Thermodynamics of the brane in Chern-Simons matter theories with flavor

We study the holographic dual of flavors in a Chern-Simons matter theory at non-zero temperature, realized as D6-branes in the type IIA black hole dual in the ABJM background geometry. We consider both massive and massless flavors. The former are treated in the quenched approximation, whereas the massless ones are considered as dynamical objects and their backreaction on the geometry is included in the black hole background. We compute the holographically renormalized action of the probe by imposing several physical conditions. In the limit of massless flavors the free energy and entropy of the probe match non-trivially the first variation of these quantities for the backreacted background when the number of flavors is increased by one unit. We compute several thermodynamical functions for the system and analyze the meson melting phase transition between Minkowski and black hole embeddings.

hep-th↗

arXiv2011

Holographic Duals of Quark Gluon Plasmas with Unquenched Flavors

We review the construction of gravitational solutions holographically dual to N=1 quiver gauge theories with dynamical flavor multiplets. We focus on the D3-D7 construction and consider the finite temperature, finite quark chemical potential case where there is a charged black hole in the dual solution. Discussed physical outputs of the model include its thermodynamics (with susceptibilities) and general hydrodynamic properties.

hep-th↗

arXiv2011

D3-D7 Quark-Gluon Plasmas at Finite Baryon Density

We present the string dual to SU(Nc) N=4 SYM, coupled to Nf massless fundamental flavors, at finite temperature and baryon density. The solution is determined by two dimensionless parameters, both depending on the 't Hooft coupling $λ_h$ at the scale set by the temperature T: $ε_h\simλ_h Nf/Nc$, weighting the backreaction of the flavor fields and $\tildeδ\simλ_h^{-1/2}nb/(Nf T^3)$, where $nb$ is the baryon density. For small values of these two parameters the solution is given analytically up to second order. We study the thermodynamics of the system in the canonical and grand-canonical ensembles. We then analyze the energy loss of partons moving through the plasma, computing the jet quenching parameter and studying its dependence on the baryon density. Finally, we analyze certain "optical" properties of the plasma. The whole setup is generalized to non abelian strongly coupled plasmas engineered on D3-D7 systems with D3-branes placed at the tip of a generic singular Calabi-Yau cone. In all the cases, fundamental matter fields are introduced by means of homogeneously smeared D7-branes and the flavor symmetry group is thus a product of abelian factors.

hep-th↗

arXiv2011

Sum rules, plasma frequencies and Hall phenomenology in holographic plasmas

We study the AC optical and hall conductivities of Dp/Dq-branes intersections in the probe approximation and use sum-rules to study various associated transport coefficients. We determine that the presence of massive fundamental matter, as compared to massless fundamental matter described holographically by a theory with no dimensional defects, reduces the plasma frequency. We further show that this is not the case when the brane intersections include defects. We discuss in detail how to implement correctly the regularization of retarded Green's functions so that the dispersion relations are satisfied and the low energy behaviour of the system is physically realistic.

hep-th↗

arXiv2009

Holographic Operator Mixing and Quasinormal Modes on the Brane

We provide a framework for calculating holographic Green's functions from general bilinear actions and fields obeying coupled differential equations in the bulk. The matrix-valued spectral function is shown to be independent of the radial bulk coordinate. Applying this framework we improve the analysis of fluctuations in the D3/D7 system at finite baryon density, where the longitudinal perturbations of the world-volume gauge field couple to the scalar fluctuations of the brane embedding. We compute the spectral function and show how its properties are related to the quasinormal mode spectrum. We study the crossover from the hydrodynamic diffusive to the reactive regime and the movement of quasinormal modes as functions of temperature and density. We also compute their dispersion relations and find that they asymptote to the lightcone for large momenta.

hep-th↗

arXiv2009

D3-D7 Quark-Gluon Plasmas

We present the string dual to finite temperature SU(Nc) N=4 SYM coupled to massless fundamental matter introduced by Nf D7 branes, with Abelian flavor symmetry. The analytic solution includes the backreaction of the flavors up to second order in the parameter that weighs the internal flavor loops, epsilon_h=(lambda_h Nf)/(8 pi^2 Nc), lambda_h being the 't Hooft coupling at the temperature of the dual Quark-Gluon Plasma. We study the thermodynamics of the system and its departure from conformality, which is a second order effect. We then analyze the energy loss of partons moving through the plasma, finding that the fundamental degrees of freedom enhance the jet quenching. The whole setup is generalized to D3-D7 systems with D3-branes placed at the tip of a generic singular Calabi-Yau cone over a five-dimensional Sasaki-Einstein manifold. We finally provide the equations for the inclusion of massive flavors in the N=4 SYM plasma.

hep-th↗

arXiv2009

A note on conductivity and charge diffusion in holographic flavour systems

We analyze the charge diffusion and conductivity in a Dp/Dq holographic setup that is dual to a supersymmetric Yang-Mills theory in p+1 dimensions with N_f<< N_c flavour degrees of freedom at finite temperature and nonvanishing U(1) baryon number chemical potential. We provide a new derivation of the results that generalize the membrane paradigm to the present context. We perform a numerical analysis in the particular case of the D3/D7 flavor system. The results obtained support the validity of the Einstein relation at finite chemical potential.

hep-th↗

arXiv2009

Enumeration of lifts of commuting elements of a group

Given commuting elements a, b of a group G and a group epimorphism q : G' \to G with finite kernel, the set of commuting lifts of a, b to G' is finite (possibly, empty). The second named author obtained a formula for the number of such lifts in terms of representations of Ker q. We apply this formula to several group epimorphisms q with the same kernel. In particular, we analyze the case where Ker q = Q_8 is the quaternion group. We show that in this case the number in question is equal to 0, 8, 16, 24, or 40. We show that all these numbers are realized by some G,G',q,a,b.

math.GR↗

arXiv2008

On the Einstein Relation in holographic systems at finite baryon density

We study the conductivity, susceptibility and diffusion of a strongly coupled quark gluon plasma from the holographic perspective. We calculate general expressions for these quantities in the presence of finite baryon density and show that in this context, for the D3/D7 intersection the Einstein relation holds, providing another non-trivial check of the holographic correspondence at finite temperature.

hep-th↗

arXiv2008

Holographic Spectral Functions at Finite Baryon Density

Using the AdS/CFT correspondence, we compute the spectral functions of thermal super Yang Mills at large N_c coupled to a small number of flavours of fundamental matter, N_f<<N_c, in the presence of a nonzero baryon density. The holographic dual of such a theory involves the addition of probe D7-branes with a background worldvolume gauge field switched on, embedded in the geometry of a stack of black D3-branes. We perform the analysis in the vector and scalar channels which become coupled for nonzero values of the spatial momentum and baryon density. In addition, we obtain the effect of the presence of net baryon charge on the photon production. We also extract the conductivity and find perfect agreement with the results derived by Karch and O'Bannon in a macroscopic setup.

hep-th↗

arXiv2007

The shear viscosity of the non-commutative plasma

We compute the shear viscosity of the non-commutative N=4 super Yang-Mills quantum field theory at strong coupling using the dual supergravity background. Special interest derives from the fact that the background presents an intrinsic anisotropy in space through the distinction of commutative and non-commutative directions. Despite this anisotropy the analysis exhibits the ubiquitous result η/s = 1/4πfor two different shear channels. In order to derive this result, we show that the boundary energy momentum tensor must couple to the open string metric. As a byproduct we compute the renormalised holographic energy momentum tensor and show that it coincides with one in the commutative theory.

hep-th↗

arXiv2007

Hydrodynamics from the Dp-brane

We complete the computation of viscous transport coefficients in the near horizon geometries that arise from a stack of black Dp-branes for p=2,...,6 in the decoupling limit. The main new result is the obtention of the bulk viscosity which, for all p, is found to be related to the speed of sound by the simple relation ζ/η= -2(v_s^2-1/p). For completeness the shear viscosity is rederived from gravitational perturbations in the shear and scalar channels. We comment on technical issues like the counterterms needed, or the possible dependence on the conformal frame.

hep-th↗

arXiv2006

Jet quenching at finite `t Hooft coupling and chemical potential from AdS/CFT

Following the nonperturbative prescription for the jet quenching parameter recently proposed by Liu, Rajagopal and Wiedemann, we compute the first correction in the inverse `t Hooft coupling corresponding to string alpha' corrections in the dual background. We also consider the introduction of a chemical potential for the U(1)^3 gauged R-symmetry. While the former mildly diminishes the jet quenching parameter -this suggesting a smooth interpolation between the strong coupling and perturbative results-, the latter generically increases its value. We comment on the extension of this setup to quarks of finite mass.

hep-ph↗

arXiv2004

Localized Intersections of Non-Extremal p-branes and S-branes

A class of solutions to Supergravity in 10 or 11 dimensions is presented which extends the non-standard or semi-local intersections of Dp-branes to the case of non-extremal p-branes. The type of non-extremal solutions involved in the intersection is free and we provide two examples involving black-branes and/or D-\bar{D} systems. After a rotation among the time coordinate and a relatively transverse radial direction the solutions admit the interpretation of an intersection among D-branes and S-branes. We speculate on the relevance of these configurations both to study time dependent phenomena in the AdS/CFT correspondence as well as to construct cosmological brane-world scenarios within String Theory admitting accelerating expansion of the Universe.

hep-th↗

arXiv2000

Phases of dual superconductivity and confinement in softly broken N=2 supersymmetric Yang-Mills theories

We study the electric flux tubes that undertake color confinement in N=2 supersymmetric Yang-Mills theories softly broken down to N=1 by perturbing with the first two Casimir operators. The relevant Abelian Higgs model is not the standard one due to the presence of an off-diagonal coupling among different magnetic U(1) factors. We perform a preliminary study of this model at a qualitative level. BPS vortices are explicitely obtained for particular values of the soft breaking parameters. Generically however, even in the ultrastrong scaling limit, vortices are not critical but live in a "hybrid" type II phase. Also, ratios among string tensions are seen to follow no simple pattern. We examine the situation at the half Higgsed vacua and find evidence for solutions with the behaviour of superconducting strings. In some cases they are solutions to BPS equations.

hep-th↗

arXiv1999

N=2 supersymmetric gauge theories with massive hypermultiplets and the Whitham hierarchy

We embed the Seiberg-Witten solution for the low energy dynamics of N=2 super Yang-Mills theory with an even number of massive hypermultiplets into the Whitham hierarchy. Expressions for the first and second derivatives of the prepotential in terms of the Riemann theta function are provided which extend previous results obtained by Gorsky, Marshakov, Mironov and Morozov. Checks in favour of the new equations involve both their behaviour under duality transformations and the consistency of their semiclassical expansions.

hep-th↗

arXiv1999

Instanton corrections in N=2 supersymmetric theories with classical gauge groups and fundamental matter hypermultiplets

We compute instanton corrections to the low energy effective prepotential of N=2 supersymmetric theories in a variety of cases, including all classical gauge groups and even number of fundamental matter hypermultiplets. To this end, we take profit of a set of first- and second-order equations for the logarithmic derivatives of the prepotential with respect to the dynamical scale expressed in terms of Riemann's theta-function. These equations emerge in the context of the Whitham hierarchy approach to the low-energy Seiberg--Witten solution of supersymmetric gauge theories. Our procedure is recursive and allows to compute the effective prepotential to arbitrary order in a remarkably straightforward way. General expressions for up to three-instanton corrections are given. We illustrate the method with explicit expressions for several cases.

hep-th↗