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We construct a family of closed string solutions with kinks in a subspace of AdS_5 x S^5 and study their properties. In certain limits these solutions become folded pulsating strings, although in general they are made of multiple pulsating rectangles. One unusual feature of these solutions is that their monodromy matrices are trivial, leading to vanishing quasi-momenta. Exact Backlund transformations of these solutions are found, again giving vanishing higher conserved charges. We also consider the fluctuation modes around these solutions as well as the semiclassical splitting of these strings., Comment: 35 pages, 6 figures; Version 2 references added

We study a spherical antimembrane in the eleven dimensional pp wave. In this background, a single antimembrane breaks all the supersymmetries because its dipole is misaligned with the background flux. Using the BMN matrix theory we compute the one-loop potential for the antimembrane. Then we put the antimembrane in the field produced by a source spherical membrane and compute the velocity-dependent part of the interaction between them on both the supergravity side and the BMN matrix theory side. Despite the aforementioned nonsupersymmetry of the antimembrane, it is found that the results on the two sides completely agree., Comment: 14 pages REVTeX and AMSLaTeX, plus appendices, for a total of 29 pages; v2: reference added; v3: minor changes (footnote and clarification added)

We examine the dynamics of extended branes, carrying lower dimensional brane charges, wrapping black holes and black hole microstates in M and Type II string theory. We show that they have a universal dispersion relation typical of threshold bound states with a total energy equal to the sum of the contributions from the charges. In near-horizon geometries of black holes, these are BPS states, and the dispersion relation follows from supersymmetry as well as properties of the conformal algebra. However they break all supersymmetries of the full asymptotic geometries of black holes and microstates. We comment on a recent proposal which uses these states to explain black hole entropy., Comment: 41 pages, 2 figures;v2: references added

We investigate the gauge/gravity duality in the interaction between two spherical membranes in the 11-dimensional pp-wave background. On the supergravity side, we find the solution to the field equations at locations close to a spherical source membrane, and use it to obtain the light cone Lagrangian of a spherical probe membrane very close to the source, i.e., with their separation much smaller than their radii. On the gauge theory side, using the BMN matrix model, we compute the one-loop effective potential between two membrane fuzzy spheres. Perfect agreement is found between the two sides. Moreover, the one-loop effective potential we obtain on the gauge theory side is valid beyond the small-separation approximation, giving the full interpolation between interactions of membrane-like objects and that of graviton-like objects., Comment: 34 pages

In a certain kinematic limit, where the effects of spacetime curvature (and other background fields) greatly simplify, the light-cone gauge world-sheet action for a type IIB superstring on AdS_5 x S^5 reduces to that of a free field theory. It has been conjectured by Berenstein, Maldacena, and Nastase that the energy spectrum of this string theory matches the dimensions of operators in the appropriately defined large R-charge large-N_c sector of N=4 supersymmetric Yang--Mills theory in four dimensions. This holographic equivalence is thought to be exact, independent of any simplifying kinematic limits. As a step toward verifying this larger conjecture, we have computed the complete set of first curvature corrections to the spectrum of light-cone gauge string theory that arises in the expansion of AdS_5 x S^5 about the plane-wave limit. The resulting spectrum has the complete dependence on lambda = g_YM^2 N_c; corresponding results in the gauge theory are known only to second order in lambda. We find precise agreement to this order, including the N=4 extended supermultiplet structure. In the process, we demonstrate that the complicated schemes put forward in recent years for defining the Green--Schwarz superstring action in background Ramond-Ramond fields can be reduced to a practical (and correct) method for quantizing the string., Comment: 39 pages; substantial improvements

We compute the two-body one-loop effective action for the matrix theory in the pp-wave background, and compare it to the effective action on the supergravity side in the same background. Agreement is found for the effective actions on both sides. This points to the existence of a supersymmetric nonrenormalization theorem in the pp-wave background., Comment: 28 pages, LaTex, no figures; references added, to appear in Nuclear Physics B

We study vortex-creating, or monopole, operators in 3d CFTs which are the infrared limit of N=2 and N=4 supersymmetric QEDs in three dimensions. Using large-Nf expansion, we construct monopole operators which are primaries of short representations of the superconformal algebra. Mirror symmetry in three dimensions makes a number of predictions about such operators, and our results confirm these predictions. Furthermore, we argue that some of our large-Nf results are exact. This implies, in particular, that certain monopole operators in N=4 d=3 SQED with Nf=1 are free fields. This amounts to a proof of 3d mirror symmetry in a special case., Comment: 30 pages, latex. v2: references added

Many abelian gauge theories in three dimensions flow to interacting conformal field theories in the infrared. We define a new class of local operators in these conformal field theories which are not polynomial in the fundamental fields and create topological disorder. They can be regarded as higher-dimensional analogues of twist and winding-state operators in free 2d CFTs. We call them monopole operators for reasons explained in the text. The importance of monopole operators is that in the Higgs phase, they create Abrikosov-Nielsen-Olesen vortices. We study properties of these operators in three-dimensional QED using large N_f expansion. In particular, we show that monopole operators belong to representations of the conformal group whose primaries have dimension of order N_f. We also show that monopole operators transform non-trivially under the flavor symmetry group, with the precise representation depending on the value of the Chern-Simons coupling., Comment: 24 pages, latex. v2: a reference to prior work has been added