Flavor from M5-branes

We study various aspects of the defect conformal field theory that arises when placing a single M5-brane probe in AdS_4 x S^7. We derive the full set of fluctuation modes and dimensions of the corresponding dual operators. We argue that the latter does not depend on the presence of a non-trivial magnetic flux on the M5-brane world-volume. Finally we give a mass to the hypermultiplet living on the defect, and compute the resulting mesonic spectrum.Comment: 19 page

Quantum Critical Superfluid Flows and Anisotropic Domain Walls

We construct charged anisotropic AdS domain walls as solutions of a consistent truncation of type IIB string theory. These are a one-parameter family of solutions that flow to an AdS fixed point in the IR, exhibiting emergent conformal invariance and quantum criticality. They represent the zero-temperature limit of the holographic superfluids at finite superfluid velocity constructed in arXiv:1010.5777. We show that these domain walls exist only for velocities less than a critical value, agreeing in detail with a conjecture made there. We also comment about the IR limits of flows with velocities higher than this critical value, and point out an intriguing similarity between the phase diagrams of holographic superfluid flows and those of ordinary superconductors with imbalanced chemical potential.Comment: 11 pages, 3 figures. V2: Very minor corrections. JHEP versio

Universal Holographic Chiral Dynamics in an External Magnetic Field

In this work we further extend the investigation of holographic gauge theories in external magnetic fields, continuing earlier work. We study the phenomenon of magnetic catalysis of mass generation in 1+3 and 1+2 dimensions, using D3/D7- and D3/D5-brane systems, respectively. We obtain the low energy effective actions of the corresponding pseudo Goldstone bosons and study their dispersion relations. The D3/D7 system exhibits the usual Gell-Mann--Oakes--Renner (GMOR) relation and a relativistic dispersion relation, while the D3/D5 system exhibits a quadratic non-relativistic dispersion relation and a modified linear GMOR relation. The low energy effective action of the D3/D5 system is related to that describing magnon excitations in a ferromagnet. We also study properties of general Dp/Dq systems in an external magnetic field and verify the universality of the magnetic catalysis of dynamical symmetry breaking.Comment: 41 pages, 11 figures, references adde

On unquenched N=2 holographic flavor

The addition of fundamental degrees of freedom to a theory which is dual (at low energies) to N=2 SYM in 1+3 dimensions is studied. The gauge theory lives on a stack of Nc D5 branes wrapping an S^2 with the appropriate twist, while the fundamental hypermultiplets are introduced by adding a different set of Nf D5-branes. In a simple case, a system of first order equations taking into account the backreaction of the flavor branes is derived (Nf/Nc is kept of order 1). From it, the modification of the holomorphic coupling is computed explicitly. Mesonic excitations are also discussed.Comment: 25 pages, 4 figure

Gravity duals of 2d supersymmetric gauge theories

We find new supergravity solutions generated by D5-branes wrapping a four-cycle and preserving four and two supersymmetries. We first consider the configuration in which the fivebranes wrap a four-cycle in a Calabi-Yau threefold, which preserves four supersymmetries and is a gravity dual to the Coulomb branch of two-dimensional gauge theories with N=(2,2) supersymmetry. We also study the case of fivebranes wrapping a co-associative four-cycle in a manifold of G_2-holonomy, which provides a gravity dual of N=(1,1) supersymmetric Yang-Mills theory in two dimensions. We also discuss the addition of unquenched fundamental matter fields to these backgrounds and find the corresponding gravity solutions with flavor brane sources.Comment: 34 pages + appendices; v2: minor improvement

D-brane probes on L^{abc} Superconformal Field Theories

We study supersymmetric embeddings of D-brane probes of different dimensionality in the AdS_5xL^{abc} background of type IIB string theory. In the case of D3-branes, we recover the known three-cycles dual to the dibaryonic operators of the gauge theory and we also find a new family of supersymmetric embeddings. Supersymmetric configurations of D5-branes, representing fractional branes, and of spacetime filling D7-branes (which can be used to add flavor) are also found. Stable non supersymmetric configurations corresponding to fat strings and domain walls are found as well.Comment: 20 pages, LaTeX;v2: minor improvements, references adde

Holographic Josephson Junctions and Berry holonomy from D-branes

We construct a holographic model for Josephson junctions with a defect system of a Dp brane intersecting a D(p+2) brane. In addition to providing a geometrical picture for the holographic dual, this leads us very naturally to suggest the possibility of non-Abelian Josephson junctions characterized in terms of the topological properties of the branes. The difference between the locations of the endpoints of the Dp brane on either side of the defect translates into the phase difference of the condensate in the Josephson junction. We also add a magnetic flux on the D(p+2) brane and allow it evolve adiabatically along a closed curve in the space of the magnetic flux, while generating a non-trivial Berry holonomy.Comment: 20 pages, 2 figure

Holographic flavor on the Higgs branch

In this paper we study the holographic dual, in several spacetime dimensions, of the Higgs branch of gauge theories with fundamental matter. These theories contain defects of various codimensionalities, where the matter fields are located. In the holographic description the matter is added by considering flavor brane probes in the supergravity backgrounds generated by color branes, while the Higgs branch is obtained when the color and flavor branes recombine with each other. We show that, generically, the holographic dual of the Higgs phase is realized by means of the addition of extra flux on the flavor branes and by choosing their appropriate embedding in the background geometry. This suggests a dielectric interpretation in terms of the color branes, whose vacuum solutions precisely match the F- and D-flatness conditions obtained on the field theory side. We further compute the meson mass spectra in several cases and show that when the defect added has codimension greater than zero it becomes continuous and gapless.Comment: 59 pages, 1 figure;v2: references adde

Holographic mesons in various dimensions

We calculate the spectrum of fluctuations of a probe Dk-brane in the background of N Dp-branes, for k=p,p+2,p+4 and p< 5. The result corresponds to the mesonic spectrum of a (p+1)-dimensional super-Yang-Mills (SYM) theory coupled to `dynamical quarks', i.e., fields in the fundamental representation -- the latter are confined to a defect for k=p and p+2. We find a universal behaviour where the spectrum is discrete and the mesons are deeply bound. The mass gap and spectrum are set by the scale M ~ m_q/g_{eff}(m_q), where m_q is the mass of the fundamental fields and g_{eff}(m_q) is the effective coupling evaluated at the quark mass, i.e. g_{eff}^2(m_q)=g_{ym}^2 N m_q^{p-3}. We consider the evolution of the meson spectra into the far infrared of three-dimensional SYM, where the gravity dual lifts to M-theory. We also argue that the mass scale appearing in the meson spectra is dictated by holography.Comment: 44 pages, 2 figures; v2: typos corrected, references adde

Mesons in marginally deformed AdS/CFT

We study the embedding of spacetime filling D7-branes in beta-deformed backgrounds which, according to the AdS/CFT dictionary, corresponds to flavoring beta-deformed N=4 super Yang-Mills. We consider supersymmetric and more general non-supersymmetric three parameter deformations. The equations of motion for quadratic fluctuations of a probe D7-brane wrapped on a deformed three-sphere exhibit a non-trivial coupling between scalar and vector modes induced by the deformation. Nevertheless, we manage to solve them analytically and find that the mesonic mass spectrum is discrete, with a mass gap and a Zeeman-like splitting occurs. Finally we propose the action for the dual field theory as obtained by star-product deformation of super Yang-Mills with fundamental matter.Comment: LaTex, 42 pages, 3 figures, uses JHEP