Calibrations, Monopoles and Fuzzy Funnels

We present new non-Abelian solitonic configurations in the low energy effective theory describing a collection of N parallel D1--branes. These configurations preserve 1/4, 1/8, 1/16 and 1/32 of the spacetime supersymmetry. They are solutions to a set of generalised Nahm's equations which are related to self-duality equations in eight dimensions. Our solutions represent D1--branes which expand into fuzzy funnel configurations ending on collections of intersecting D3--branes. Supersymmetry dictates that such intersecting D3--branes must lie on a calibrated three-surface of spacetime and we argue that the generalised Nahm's equations encode the data for the construction of magnetic monopoles on the relevant three-surfaces.Comment: 19 pages. Latex. v2: added references and acknowledgmen

Exotic Scalar States in the AdS/CFT Correspondence

We investigate a family of solutions of Type IIb supergravity which asymptotically approach AdS_5 X S^5 but contain a non-constant dilaton and volume scalar for the five-sphere. These solutions preserve an SO(1,3) X SO(6) symmetry. We discuss the solution in the context of the AdS/CFT correspondence, and we find that as well as running coupling from the nontrivial dilaton, the corresponding field theory has no supersymmetry and displays confinement at least for a certain range of parameters.Comment: 18 pages. 3 figures. Revised discussion section, added references. Final version to appear in JHE

Spin-Two Glueballs, Positive Energy Theorems and the AdS/CFT Correspondence

We determine the spectrum of graviton excitations in the background geometry of the AdS soliton in p+2 dimensions. Via the AdS/CFT correspondence this corresponds to determining the spectrum of spin two excitations in the dual effective p-dimensional field theories For the cases of D3- and M5-branes these are the spin two glueballs of QCD_3 and QCD_4 respectively. For all values of p we find an exact degeneracy of the spectra of these tensor states and certain scalar excitations. Our results also extend the perturbative proof of a positive energy conjecture for asymptotically locally AdS spacetimes (originally proposed for p=3) to an arbritrary number of dimensions.Comment: 25 pages, 3 figure

Intersecting Branes, Defect Conformal Field Theories and Tensionless Strings

The defect conformal field theory describing intersecting D3-branes at a C^2/Z_k orbifold is used to (de)construct the theory of intersecting M5-branes, as well as M5-branes wrapping the holomorphic curve xy=c. The possibility of a 't Hooft anomaly due to tensionless strings at the intersection is discussed. This note is based on a talk given by Zachary Guralnik at the 35th International Symposium Ahrenshoop on the Theory of Elementary Particles.Comment: latex, one figure, 9pages. Talk given by Z.G. at the 35th International Symposium Ahrenshoop on the Theory of Elementary Particle

The Entropy of 4D Black Holes and the Enhancon

We consider the physics of enhancons as applied to four dimensional black holes which are constructed by wrapping both D-branes and NS-branes on K3. As was recently shown for the five dimensional black holes, the enhancon is crucial in maintaining consistency with the second law of thermodynamics. This is true for both the D-brane and NS-brane sectors of these black holes. In particular NS5-branes in both type IIA and IIB string theory are found to exhibit enhancon physics when wrapped on a K3 manifold.Comment: 23 pages. 1 figure. Minor typos corrected. Refs added. To appear in PR

Dynamical Stability of Six-Dimensional Warped Brane-Worlds

We study a generalization of the Randall-Sundrum mechanism for generating the weak/Planck hierarchy, which uses two rather than one warped extra dimension, and which requires no negative tension branes. A 4-brane with one exponentially large compact dimension plays the role of the Planck brane. We investigate the dynamical stability with respect to graviton, graviphoton and radion modes. The radion is shown to have a tachyonic instability for certain models of the 4-brane stress-energy, while it is stable in others, and massless in a special case. If stable, its mass is in the milli-eV range, for parameters of the model which solve the hierarchy problem. The radion is shown to couple to matter with gravitational strength, so that it is potentially detectable by submillimeter-range gravity experiments. The radion mass can be increased using a bulk scalar field in the manner of Goldberger and Wise, but only to order MeV, due to the effect of the large extra dimension. The model predicts a natural scale of 10^{13} GeV on the 4-brane, making it a natural setting for inflation from the ultraviolet brane.Comment: 28 pages, 7 figure

The Noncommutative Bion Core

We examine noncommutative solutions of the nonabelian theory on the world-volume of N coincident D-strings. These solutions can be interpreted in terms of noncommutative geometry as funnels describing the nonabelian D-string expanding out into an orthogonal D3-brane. These configurations are `dual' to the bion solutions in the abelian world-volume theory of the D3-brane. In the latter, a charge N magnetic monopole describes N D-strings attached to the D3-brane with a spike deformation of the world-volume. The noncommutative D-string solutions give a reliable account of physics at the core of the monopole, where the bion description is expected to breakdown. In the large N limit, we find good agreement between the two points of view, including the energy, couplings to background fields, and the shape of the funnel. We also study fluctuations traveling along the D-string, again obtaining agreement in the large N limit. At finite N, our results give a limit on the number of modes that can travel to infinity along the N D-strings attached to the D3-brane.Comment: 22 pages, refs adde

(De)constructing Intersecting M5-branes

We describe intersecting M5-branes, as well as M5-branes wrapping the holomorphic curve xy=c, in terms of a limit of a defect conformal field theory with two-dimensional (4,0) supersymmetry. This dCFT describes the low-energy theory of intersecting D3-branes at a C^2/Z_k orbifold. In an appropriate k -> infinity limit, two compact spatial directions are generated. By identifying moduli of the M5-M5 intersection in terms of those of the dCFT, we argue that the SU(2)_L R-symmetry of the (4,0) defect CFT matches the SU(2) R-symmetry of the N =2, d=4 theory of the M5-M5 intersection. We find a 't Hooft anomaly in the SU(2)_L R-symmetry, suggesting that tensionless strings give rise to an anomaly in the SU(2) R-symmetry of intersecting M5-branes.Comment: latex, 25 pages, 4 figure