AdS Black Hole Background Research Articles

Holographic Higgs phases

We discuss phases of gauge theories in the holographic context, and formulate a criterion for the existence of a Higgs phase, where the gauge redundancy is "spontaneously broken", in purely bulk language. This condition, the existence of a finite tension solitonic string representing a narrow magnetic flux tube, is necessary for a bulk theory to be interpreted as a Higgs phase of a boundary gauge theory. We demonstrate the existence of such solitons in both top-down and bottom-up examples of holographic theories. In particular, we numerically construct new solitonic solutions in AdS black hole background, for various values of the boundary gauge coupling, which are used to demonstrate that the bulk theory models a superconductor, rather than a superfluid. The criterion we find is expected to be useful in finding holographic duals of color superconducting phases of gauge theories at finite density.

Vortex and droplet in holographic D-wave superconductors

We investigate non-trivial localized solutions of the condensate in a (2+1)-dimensional D-wave holographic superconductor model in the presence of a background magnetic field. The calculation is done in the context of the (3+1)-dimensional dual gravity theory of a charged massive spin-2 field in an AdS black hole background. By using numeric techniques, we find both vortex and droplet solutions. These solutions are important for studying the full phase diagram of D-wave superconductors.

Various types of phase transitions in the AdS soliton background

We study the basic holographic insulator and superconductor phase transition in the AdS soliton background by generalizing the spontaneous breaking of a global U(1) symmetry to occur via Stückelberg mechanism. We construct the soliton solutions with backreaction and examine the effects of the backreaction on the condensation of the scalar hair in the generalized Stückelberg Lagrangian. We disclose rich physics in various phase transitions. In addition to the AdS soliton configuration, we also examine the property of the phase transition in the AdS black hole background.

Holographic phase transition from dyons in an AdS black hole background

We construct a dyon solution for a Yang-Mills-Higgs theory in a 4 dimensional Schwarzschild-anti-de Sitter black hole background with temperature T. We then apply the AdS/CFT correspondence to describe the strong coupling regime of a 2+1 quantum field theory which undergoes a phase transition exhibiting the condensation of a composite charge operator below a critical temperature $T_c$.

The Dirac equation in Kerr–Newman–Ads black hole background

We consider the Dirac equation on the Kerr–Newman–AdS black hole background. We first perform the variable separation for the Dirac equation and define the Hamiltonian operator Ĥ. Then we show that for a massive Dirac field with mass μ≥1/(2l), where l is linked to the cosmological constant Λ by Λ≕−3/l2, essential self-adjointness of Ĥ on C0∞((r+,∞)×S2)4 is obtained even in presence of the boundarylike behavior of infinity in an asymptotically AdS black hole background. Furthermore, qualitative spectral properties of the Hamiltonian are taken into account and in agreement with the existing results concerning the case of stationary axisymmetric asymptotically flat black holes we infer the absence of time-periodic and normalizable solutions of the Dirac equation around the black hole in the nonextremal case.

Flavor superconductivity from gauge/gravity duality

We give a detailed account and extensions of a holographic flavor supercon- ductivity model which we have proposed recently. The model has an explicit field theory realization as strongly coupled N = 2 Super Yang-Mills theory with fundamental matter at finite temperature and finite isospin chemical potential. Using gauge/gravity duality, i.e. a probe of two flavor D7-branes in the AdS black hole background, we show that the system undergoes a second order phase transition with critical exponent 1/2. The new ground state may be interpreted as a ρ meson superfluid. It shows signatures known from superconductivity, such as an infinite dc conductivity and a gap in the frequency-dependent conductivity. We present a stringy picture of the condensation mechanism in terms of a recombination of strings. We give a detailed account of the evaluation of the non-Abelian Dirac-Born-Infeld action involved using two different methods. Finally we also consider the case of massive flavors and discuss the holographic Meissner-Ochsenfeld effect in our scenario.

Superconductivity from gauge/gravity duality with flavor

We consider thermal strongly-coupled N=2 SYM theory with fundamental matter at finite isospin chemical potential. Using gauge/gravity duality, i.e. a probe of two flavor D7-branes embedded in the AdS black hole background, we find a critical temperature at which the system undergoes a second order phase transition. The critical exponent of this transition is one half and coincides with the result from mean field theory. In the thermodynamically favored phase, a flavor current acquires a vev and breaks an Abelian symmetry spontaneously. This new phase shows signatures known from superconductivity, such as an infinite dc conductivity and a gap in the frequency-dependent conductivity. The gravity setup allows for an explicit identification of the degrees of freedom in the dual field theory, as well as for a dual string picture of the condensation process.

FRW cosmology and equations of state on the brane

In this talk we want to point out an interesting connection between the equations of state of a field theory living on a four-dimensional brane and the FRW equations describing the cosmological evolution of the brane in the background of a five-dimensional charged AdS-black hole. This presentation is based on [G.L. Cardoso and V. Grass, Nucl. Phys. B803 (2008) 209–233 [ 0803.2819 ]].

Hydrodynamics of holographic superconductors

We study the poles of the retarded Green functions of a holographic superconductor. The model shows a second order phase transition where a charged scalar operator condenses and a U(1) symmetry is spontaneously broken. The poles of the holographic Green functions are the quasinormal modes in an AdS black hole background. We study the spectrum of quasinormal frequencies in the broken phase, where we establish the appearance of a massless or hydrodynamic mode at the critical temperature as expected for a second order phase transition. In the broken phase we find the pole representing second sound. We compute the speed of second sound and its attenuation length as function of the temperature. In addition we find a pseudo diffusion mode, whose frequencies are purely imaginary but with a non-zero gap at zero momentum. This gap goes to zero at the critical temperature. As a technical side result we explain how to calculate holographic Green functions and their quasinormal modes for a set of operators that mix under the RG flow.

Temperature versus acceleration: the Unruh effect for holographic models

We analyse the effect of velocity and acceleration on the temperature felt by particles and strings in backgrounds relevant in holographic models. First, we compare accelerated strings and strings at finite temperature. We find that for fixed Unruh temperature felt by the string endpoints, the screening length is smaller for the accelerated Wilson loop than for the static one in a thermal background of the same temperature; hence acceleration provides a ``more efficient'' mechanism for melting of mesons. Secondly, we show that the velocity-dependence of the screening length of the colour force, previously obtained from a moving Wilson loop in a finite temperature background, is not specific for the string, but is a consequence of the generic fact that an observer which moves with constant velocity in a black hole background measures a velocity-dependent temperature. Finally, we analyse accelerated particles and strings in the AdS black hole background, and show that these feel a temperature which increases as a function of time. As a byproduct of our analysis we find a global Minkowski embedding for the planar AdS black hole.

AdS black holes as reflecting cavities

We use the identification between null singularities of correlators in the bulk with time singularities in the boundary correlators to study the analytic structure of time-dependent thermal Green functions using the eikonal approximation for classical solutions in the AdS black hole background. We show that the location of singularities in complex time can be understood in terms of null rays bouncing on the boundaries and singularities of the eternal black hole, giving the picture of a `reflecting cavity'. We can then extract the general analytic expression for the asymptotic values of the frequencies of quasinormal modes in large AdS black holes.

Quantum effects for the Dirac field in a Reissner–Nordström–AdS black hole background

The behavior of a charged massive Dirac field on a Reissner–Nordström–AdS black hole background is investigated. We first analyze the problem of the essential self-adjointness of the Dirac Hamiltonian, which is made difficult by the boundary-like behavior of spatial infinity, and we find that the Hamiltonian is essentially self-adjoint iff ; moreover, we determine the essential spectrum of the Hamiltonian. Then we focus on the analysis of the discharge problem for the case . We follow the Ruffini–Damour–Deruelle approach and, as in the standard Reissner–Nordström black hole case, we find that the existence of level-crossing between the positive and negative energy solutions of the Dirac equation is at the root of the pair-creation process associated with the discharge of the black hole.

Absorption lengths in the holographic plasma

We consider the effect of a periodic perturbation with frequency $\omega$ on the holographic N=4 plasma represented by the planar AdS black hole. The response of the system is given by exponentially decaying waves. The corresponding complex wave numbers can be found by solving wave equations in the AdS black hole background with infalling boundary conditions on the horizon in an analogous way as in the calculation of quasinormal modes. The complex momentum eigenvalues have an interpretation as poles of the retarded Green's functions, where the inverse of the imaginary part gives an absorption length $\lambda$. At zero frequency we obtain the screening length for a static field. These are directly related to the glueball masses in the dimensionally reduced theory. We also point out that the longest screening length corresponds to an operator with non-vanishing R-charge and thus does not have an interpretation as a QCD3 glueball.

Chiral symmetry breaking and pions in nonsupersymmetric gauge/gravity duals

We study gravity duals of large N non-supersymmetric gauge theories with matter in the fundamental representation by introducing a D7-brane probe into deformed AdS backgrounds. In particular, we consider a D7-brane probe in both the AdS Schwarzschild black hole solution and in the background found by Constable and Myers, which involves a non-constant dilaton and S^5 radius. Both these backgrounds exhibit confinement of fundamental matter and a discrete glueball and meson spectrum. We numerically compute the quark condensate and meson spectrum associated with these backgrounds. In the AdS-black hole background, a quark-bilinear condensate develops only at non-zero quark mass. We speculate on the existence of a third order phase transition at a critical quark mass where the D7 embedding undergoes a geometric transition. In the Constable-Myers background, we find a chiral symmetry breaking condensate as well as the associated Goldstone boson in the limit of small quark mass. The existence of the condensate ensures that the D7-brane never reaches the naked singularity at the origin of the deformed AdS space.

Engineering a Bosonic AdS/CFT Correspondence

We search for a bosonic (nonsupersymmetric) string/gauge theory correspondence by using the ten-dimensional IIB and 0B strings as a guide. Our construction is based on the low-energy bosonic string effective action modified by an extra form flux. We prove that the closed string tachyon can be stabilized in this context, when the AdS scalem L does not exceed a certain critical value, L<L c . The extra form may be nonperturbatively generated as a soliton from 3-string junctions, similarly to the known nonperturbative (Jackiw–Rebbi–'t Hooft–Hasenfratz) mechanism in gauge theories, as was recently argued by David, Minwalla and Núñez. We find a stable AdS 13×S13 solution that implies the existence of a 12-dimensional AdS-boundary conformal field theory with the SO(14) global symmetry in the large N't Hooft limit, which is similar to the recently proposed bosonic M-theory of Horowitz and Susskind. Taking the proposed bosonic AdS/CFT correspondence for granted, we generalize it to finite temperature. The corresponding "glueball" masses in higher space–time dimensions are calculated from the dilaton wave equation in the AdS black hole background.

Orbiting Strings in AdS Black Holes and Script N = 4 SYM at Finite Temperature

Following Gubser, Klebanov and Polyakov [hep-th/0204051], we study strings in AdS black hole backgrounds. With respect to the pure AdS case, rotating strings are replaced by orbiting strings. We interpret these orbiting strings as CFT states of large spin similar to glueballs propagating through a gluon plasma. The energy and the spin of the orbiting string configurations are associated with the energy and the spin of states in the dual finite temperature N=4 SYM theory. We analyse in particular the limiting cases of short and long strings. Moreover, we perform a thermodynamic study of the angular momentum transfer from the glueball to the plasma by considering string orbits around rotating AdS black holes. We find that standard expectations, such as the complete thermal dissociation of the glueball, are borne out after subtle properties of rotating AdS black holes are taken into account.