No abstract

We construct a black hole geometry dual to a (2+1)-dimensional defect in an ambient (3+1)-dimensional gauge theory at non-zero temperature and quark density. The geometry is a solution to the equations of motion of type IIB supergravity with brane sources, a low energy limit of an intersection of stacks of color D3-branes and flavor D5-branes. We consider the case in which the number of D5-branes is large and they can be homogeneously distributed along the directions orthogonal to the defect, creating in this way a multilayer structure. The quark density is generated by exciting a gauge field in the worldvolume of the dynamic brane sources. We study the thermodynamics of the anisotropic black hole and compute the energy density of the dual theory, as well as the pressures and speeds of sound along the directions parallel and orthogonal to the defect. We also calculate transport coefficients in the shear channel, quark-antiquark potentials, and the entanglement entropies for slab subregions. These analyses give us a good overview on how the degrees of freedom are spread, entangled, and behave in this unquenched system in the deconfining phase at strong coupling.

We study the response of a (2+1)-dimensional gauge theory to an external rotating electric field. In the strong coupling regime such system is formulated holographically in a top-down model constructed by intersecting D3- and D5-branes along 2+1 dimensions, in the quenched approximation, in which the D5-brane is a probe in the AdS5 × $$ {\mathbbm{S}}^5 $$ S 5 geometry. The system has a non-equilibrium phase diagram with conductive and insulator phases. The external driving induces a rotating current due to vacuum polarization (in the insulator phase) and to Schwinger effect (in the conductive phase). For some particular values of the driving frequency the external field resonates with the vector mesons of the model and a rotating current can be produced even in the limit of vanishing driving field. These features are in common with the (3+1) dimensional setup based on the D3-D7 brane model [26, 27] and hint on some interesting universality. We also compute the conductivities paying special attention to the photovoltaic induced Hall effect, which is only present for massive charged carriers. In the vicinity of the Floquet condensate the optical Hall coefficient persists at zero driving field, signalling time reversal symmetry breaking.

We continue the study in [1] of a strongly coupled (2+1)-dimensional gauge theory subject to an external rotating electric field. The system is modelled holographically as a D3/D5 probe intersection. We add temperature to the D3 background and analyze the phase diagram. Also here, the conductive phase extends down to vanishing external electric field at discrete values of the frequencies where vector meson Floquet condensates form. For all temperatures, at given intercalated frequencies, we find new dual states that we name Floquet suppression points where the vacuum polarization vanishes even in the presence of an electric field. From the data we infer that these states exist both in the conductive and insulating phases. In the massless limit we find a linear and instantaneous conductivity law, recovering known general results in 2+1 dimensions. We also examine the photovoltaic AC and DC current as the response to an oscillating probe electric field and see that rising the temperature suppresses the photovoltaic Hall current. All the results obtained carry over qualitatively unaltered to the case of D3/D7.