Noncompact gaugings, chiral reduction and dual sigma models in supergravity

We show that the half-maximal SU(2) gauged supergravity with topological mass term admits coupling of an arbitrary number of n vector multiplets. The chiral circle reduction of the ungauged theory in the dual 2-form formulation gives N=(1,0) supergravity in 6D coupled to 3p scalars that parametrize the coset SO(p,3)/SO(p)x SO(3), a dilaton and (p+3) axions with p < n+1. Demanding that R-symmetry gauging survives in 6D is shown to put severe restrictions on the 7D model, in particular requiring noncompact gaugings. We find that the SO(2,2) and SO(3,1) gauged 7D supergravities give a U(1)_R, and the SO(2,1) gauged 7D supergravity gives an Sp(1)_R gauged chiral 6D supergravities coupled to certain matter multiplets. In the 6D models obtained, with or without gauging, we show that the scalar fields of the matter sector parametrize the coset SO(p+1,4)/SO(p+1)x SO(4), with the (p+3) axions corresponding to its abelian isometries. In the ungauged 6D models, upon dualizing the axions to 4-form potentials, we obtain coupling of p linear multiplets and one special linear multiplet to chiral 6D supergravity.Comment: 41 pages, late

Gauged D=7 Supergravity on the S**1/Z_2 Orbifold

We construct the most general couplings of a bulk seven-dimensional Yang-Mills-Einstein N=2 supergravity with a boundary six-dimensional chiral N=(0,1) theory of vectors and charged hypermultiplets. The boundary consists of two brane worlds sitting at the fixed points of an S^1/Z_2 compactification of the seven-dimensional bulk supergravity. The resulting 6D massless spectrum surviving the orbifold projection is anomalous. By introducing boundary fields at the orbifold fixed points, we show that all anomalies are cancelled by a Green-Schwarz mechanism. In addition, all couplings of the boundary fields to the bulk are completely specified by supersymmetry. We emphasize that there is no bulk Chern-Simons term to cancel the anomalies. The latter is traded for a Green-Schwarz term which emerges in the boundary theory after a duality transformation implemented to construct the bulk supergravity.Comment: LaTeX, 42 pages; typos corrected, reference added, version to appear in Phys. Rev.

Flux compactifications and supersymmetry breaking in 6D gauged supergravity

We review on a recent construction of the on-shell supersymmetric brane action for the codimension-two branes with nonzero tension in the flux compactification of a 6D chiral gauged supergravity. On dimesionally reducing on 4D gauged supergravity for a new supersymmetric unwarped background with conical branes, we consider the modulus stabilization for determining the soft masses of the scalars localized on the branes and show that the bulk U(1)_R provides a new mechanism for mediating the SUSY breaking.Comment: 12 pages, no figures, Invited review for Modern Physics Letters A, Published versio

Non-singlet Baryons in Less Supersymmetric Backgrounds

We analyze the holographic description of non-singlet baryons in various backgrounds with reduced supersymmetries and/or confinement. We show that they exist in all AdS_5xY_5 backgrounds with Y_5 an Einstein manifold bearing five form flux, for a number of quarks 5N/8< k< N, independently on the supersymmetries preserved. This result still holds for gamma_i deformations. In the confining Maldacena-Nunez background non-singlet baryons also exist, although in this case the interval for the number of quarks is reduced as compared to the conformal case. We generalize these configurations to include a non-vanishing magnetic flux such that a complementary microscopical description can be given in terms of lower dimensional branes expanding into fuzzy baryons. This description is a first step towards exploring the finite 't Hooft coupling region.Comment: 36 Pages, 1 figure, Latex, v2: few minor changes, JHEP versio

Three-dimensional AdS gravity and extremal CFTs at c=8m

We note that Witten's proposed duality between extremal c=24k CFTs and three-dimensional anti-de Sitter gravity may possibly be extended to central charges that are multiples of 8, for which extremal self-dual CFTs are known to exist up to c=40. All CFTs of this type with central charge 24 or higher, provided that they exist, have the required mass gap and may serve as candidate duals to three-dimensional gravity at the corresponding values of the cosmological constant. Here, we compute the genus one partition function of these theories up to c=88, we give exact and approximate formulas for the degeneracies of states, and we determine the genus two partition functions of the theories up to c=40.Comment: 17 pages, harvmac; v2: references added, version accepted in JHE

Note on New Massive Gravity in AdS3AdS_3

In this note we study the properties of linearized gravitational excitations in the new massive gravity theory in asymptotically $AdS_3$ spacetime and find that there is also a critical point for the mass parameter at which massive gravitons become massless as in topological massive gravity in $AdS_3$. However, at this critical point in the new massive gravity the energy of all branches of highest weight gravitons vanish and the central charges also vanish within the Brown-Henneaux boundary conditions. The new massive gravity in asymptotically $AdS_3$ spacetime seems to be trivial at this critical point under the Brown-Henneaux boundary conditions if the Brown-Henneaux boundary conditions can be consistent with this theory. At this point, the boundary conditions of log gravity may be preferred.Comment: v3 typos corrected, refs added, version to appear in JHE

Heavy ion collisions and AdS/CFT

We review some recent applications of the AdS/CFT correspondence to heavy ion collisions including a calculation of the jet quenching parameter in N=4 super-Yang-Mills theory and quarkonium suppression from velocity scaling of the screening length for a heavy quark-antiquark pair. We also briefly discuss differences and similarities between QCD and N=4 Super-Yang-Mills theory.Comment: Plenary talk given at Quark Matter 2006, Shanghai, China, 14-20 Nov 2006; to appear in the conference proceedin

Electrified BPS Giants: BPS configurations on Giant Gravitons with Static Electric Field

We consider D3-brane action in the maximally supersymmetric type IIB plane-wave background. Upon fixing the light-cone gauge, we obtain the light-cone Hamiltonian which is manifestly supersymmetric. The 1/2 BPS solutions of this theory (solutions which preserve 16 supercharges) are either of the form of spherical three branes, the giant gravitons, or zero size point like branes. We then construct specific classes of 1/4 BPS solutions of this theory in which static electric field on the brane is turned on. These solutions are deformations about either of the two 1/2 BPS solutions. In particular, we study in some detail 1/4 BPS configurations with electric dipole on the three sphere giant, i.e. BIons on the giant gravitons, which we hence call BIGGons. We also study BPS configurations corresponding to turning on a background uniform constant electric field. As a result of this background electric field the three sphere giant is deformed to squashed sphere, while the zero size point like branes turn into circular or straight fundamental strings in the plane-wave background, with their tension equal to the background electric field.Comment: 32 pages, 1 eps figure; v2: Presentation of derivation of light-cone Hamiltonian improved, Refs adde

Towards multi-scale dynamics on the baryonic branch of Klebanov-Strassler

We construct explicitly a new class of backgrounds in type-IIB supergravity which generalize the baryonic branch of Klebanov-Strassler. We apply a solution-generating technique that, starting from a large class of solutions of the wrapped-D5 system, yields the new solutions, and then proceed to study in detail their properties, both in the IR and in the UV. We propose a simple intuitive field theory interpretation of the rotation procedure and of the meaning of our new solutions within the Papadopoulos-Tseytlin ansatz, in particular in relation to the duality cascade in the Klebanov-Strassler solution. The presence in the field theory of different VEVs for operators of dimensions 2, 3 and 6 suggests that this is an important step towards the construction of the string dual of a genuinely multi-scale (strongly coupled) dynamical model.Comment: 37 pages, 7 figures. References added, version to appear in JHE

Probing strongly coupled anisotropic plasma

We calculate the static potential, the drag force and the jet quenching parameter in strongly coupled anisotropic N=4 super Yang-Mills plasma. We find that the jet quenching is in general enhanced in presence of anisotropy compared to the isotropic case and that its value depends strongly on the direction of the moving quark and the direction along which the momentum broadening occurs. The jet quenching is strongly enhanced for a quark moving along the anisotropic direction and momentum broadening happens along the transverse one. The parameter gets lower for a quark moving along the transverse direction and the momentum broadening considered along the anisotropic one. Finally, a weaker enhancement is observed when the quark moves in the transverse plane and the broadening occurs on the same plane. The drag force for quark motion parallel to the anisotropy is always enhanced. For motion in the transverse space the drag force is enhanced compared to the isotropic case only for quarks having velocity above a critical value. Below this critical value the force is decreased. Moreover, the drag force along the anisotropic direction is always stronger than the force in the transverse space. The diffusion time follows exactly the inverse relations of the drag forces. The static potential is decreased and stronger decrease observed for quark-antiquark pair aligned along the anisotropic direction than the transverse one. We finally comment on our results and elaborate on their similarities and differences with the weakly coupled plasmas.Comment: 1+44 pages, 18 Figures; Added results on static force; Added references; version published in JHE