arXiv subjects

Andy O'Bannon

Publications and source records attributed to Andy O'Bannon.

43 records · Page 3Linked to original sources

arXiv2008

Toward a Holographic Model of Superconducting Fermions

We use the AdS/CFT correspondence to study N=4 supersymmetric SU(Nc) Yang-Mills theory, in the limits of large Nc and large 't Hooft coupling, coupled to a number Nf of massless hypermultiplet fields in the fundamental representation of the gauge group. We identify a U(1) subgroup of the R-symmetry under which the fermions in the hypermultiplet are charged but the scalars are not. All the hypermultiplet fields are also charged under a U(1) baryon number symmetry. We introduce an external magnetic field for the baryon number U(1), which triggers the spontaneous breaking of the U(1) R-symmetry, and we then introduce a chemical potential for the U(1) R-charge, producing a state with a nonzero density of the U(1) R-charge. The system should then exhibit superconductivity of the U(1) R-charge. The dual supergravity description is a number Nf of D7-branes in AdS5 x S5 with angular momentum on the S5 and a worldvolume magnetic field. We study the zero-temperature thermodynamics of the system, and find that for sufficiently large magnetic field the system prefers to be in the symmetry-broken phase. For smaller magnetic fields we find a discontinuous free energy, indicating that our gravitational setup does not capture all equilibrium states of the field theory.

hep-th↗

arXiv2008

Holographic Thermodynamics and Transport of Flavor Fields

We use gauge-gravity duality to study a strongly-coupled non-Abelian gauge theory with flavor fields, i.e. fields transforming in the fundamental representation of the gauge group. We first study the thermodynamics of the flavor fields. In the grand canonical ensemble at zero temperature, we find a second-order transition when the mass of the flavor fields equals the chemical potential. We then study the transport properties of the flavor fields at finite temperature and density. We introduce external electric and magnetic fields and compute the resulting current of flavor charge. From this current we extract the conductivity, using Ohm's law. In addition, we compute the drag force on the flavor fields at large mass, in the presence of a finite baryon density and external electric and magnetic fields.

hep-th↗

arXiv2007

Holographic Thermodynamics at Finite Baryon Density: Some Exact Results

We use the AdS/CFT correspondence to study the thermodynamics of massive N=2 supersymmetric hypermultiplets coupled to N=4 supersymmetric SU(Nc) Yang-Mills theory in the limits of large Nc and large 't Hooft coupling. In particular, we study the theory at finite baryon number density. At zero temperature, we present an exact expression for the hypermultiplets' leading-order contribution to the free energy, and in the supergravity description we clarify which D-brane configuration is appropriate for any given value of the chemical potential. We find a second-order phase transition when the chemical potential equals the mass. At finite temperature, we present an exact expression for the hypermultiplets' leading-order contribution to the free energy at zero mass.

hep-th↗

arXiv2007

Metallic AdS/CFT

We use the AdS/CFT correspondence to compute the conductivity of massive N=2 hypermultiplet fields at finite baryon number density in an N=4 SU(N_c) super-Yang-Mills theory plasma in the large N_c, large 't Hooft coupling limit. The finite baryon density provides charge carriers analogous to electrons in a metal. An external electric field then induces a finite current which we determine directly. Our result for the conductivity is good for all values of the mass, external field and density, modulo statements about the yet-incomplete phase diagram. In the appropriate limits it agrees with known results obtained from analyzing small fluctuations around equilibrium. For large mass, where we expect a good quasi-particle description, we compute the drag force on the charge carriers and find that the answer is unchanged from the zero density case. Our method easily generalizes to a wide class of systems of probe branes in various backgrounds.

hep-th↗

arXiv2007

Hall Conductivity of Flavor Fields from AdS/CFT

We use the AdS/CFT correspondence to compute a conductivity associated with massive N=2 supersymmetric hypermultiplet fields at finite baryon density, propagating through an N=4 supersymmetric SU(Nc) Yang-Mills plasma in the large Nc, large 't Hooft coupling limit. We do so by introducing external electric and magnetic fields coupled to baryon number and computing the resulting induced current, from which we extract the conductivity tensor. At large hypermultiplet mass we compute the drag force on the charge carriers. We also compute the product of the drag coefficient with the kinetic mass, and find that the answer is unchanged from the zero density case. The gravitational dual is a probe D7-brane, with a nontrivial worldvolume gauge field configuration, in an AdS-Schwarzschild background. We identify an effective horizon on the D7-brane worldvolume analogous to the worldsheet horizon observed for strings moving in the same background. We generalize our results to a class of theories described by probe D-branes in various backgrounds.

hep-th↗

arXiv2006

Chiral Transition of N=4 Super Yang-Mills with Flavor on a 3-Sphere

We use the AdS/CFT correspondence to perform a numerical study of a phase transition in strongly-coupled large-Nc N = 4 Super-Yang-Mills theory on a 3-sphere coupled to a finite number Nf of massive N = 2 hypermultiplets in the fundamental representation of the gauge group. The gravity dual system is a number Nf of probe D7-branes embedded in AdS_5 x S^5. We draw the phase diagram for this theory in the plane of hypermultiplet mass versus temperature and identify for temperatures above the Hawking-Page deconfinement temperature a first-order phase transition line across which the chiral condensate jumps discontinuously.

hep-th↗

arXiv2006

Holographic Renormalization of Probe D-Branes in AdS/CFT

We perform holographic renormalization for probe branes in AdS_5 x S^5. We show that for four known probe D-branes wrapping an AdS_m x S^n, the counterterms needed to render the action finite are identical to those for the free, massive scalar in AdS_m plus counterterms for the renormalization of the volume of AdS_m. The four cases we consider are the probe D7, two different probe D5's and a probe D3. In the D7 case there are scheme-dependent finite counterterms that can be fixed by supersymmetry.

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