S^1-wrapped D3-branes on Conifolds

We construct a D3-brane wrapped on S^1, which is fibred over the resolved conifold as its transverse space. Whereas a fractional D3-brane on the resolved conifold is not supersymmetric and has a naked singularity, our solution is supersymmetric and regular everywhere. We also consider an $S^1$-wrapped D3-brane on the resolved cone over T^{1,1}/Z_2, as well as on the deformed conifold. In the former case, we obtain a regular supergravity dual to a certain four-dimensional field theory whose Lorentz and conformal symmetries are broken in the IR region and restored in the UV limit.Comment: Latex, 14 pages, minor correction

Smooth Cosmologies from M-theory

We review two ways in which smooth cosmological evolution between two de Sitter phases can be obtained from M/string-theory. Firstly, we perform a hyperbolic reduction of massive IIA* theory to D=6 N=(1,1) SU(2)xU(1) gauged de Sitter supergravity, which supports smooth cosmological evolution between dS_4 x S^2 and a dS_6-type geometry. Secondly, we obtain four-dimensional de Sitter gravity with SU(2) Yang-Mills gauge fields from a hyperbolic reduction of standard eleven-dimensional supergravity. The four-dimensional theory supports smooth cosmological evolution between dS_2 x S^2 and a dS_4-type geometry. Although time-dependent, these solutions arise from a first-order system via a superpotential construction. For appropriate choices of charges, these solutions describe an expanding universe whose expansion rate is significantly larger in the past than in the future, as required for an inflationary model.Comment: Latex, 7 pages, Contribution to Quantum Theory and Symmetries

Non-singular Twisted S-branes From Rotating Branes

We show that rotating p-brane solutions admit an analytical continuation to become twisted Sp-branes. Although a rotating p-brane has a naked singularity for large angular momenta, the corresponding S-brane configuration is regular everywhere and exhibits a smooth bounce between two phases of Minkowski spacetime. If the foliating hyperbolic space of the transverse space is of even dimension, such as for the twisted SM5-brane, then for an appropriate choice of parameters the solution smoothly flows from a warped product of two-dimensional de Sitter spacetime, five-dimensional Euclidean space and a hyperbolic 4-space in the infinite past to Minkowski spacetime in the infinite future. We also show that non-singular S-Kerr solutions can arise from higher-dimensional Kerr black holes, so long as all (all but one) angular momenta are non-vanishing for even (odd) dimensions.Comment: Latex, 20 page

C-metrics in Gauged STU Supergravity and Beyond

We construct charged generalizations of the dilaton C-metric in various four-dimensional theories, including STU gauged supergravity as well as a one-parameter family of Einstein-Maxwell-dilaton theories whose scalar potential can be expressed in terms of a superpotential. In addition, we present time-dependent generalizations of the dilaton C-metric and dilaton Ernst solutions, for which the time evolution is driven by the dilaton. These C-metric solutions provide holographic descriptions of a strongly-coupled three-dimensional field theory on the background of a black hole, a gravitational soliton, and a black hole undergoing time evolution.Comment: 26 pages, comments and references adde

Absorption by Extremal D3-branes

The absorption in the extremal D3-brane background is studied for a class of massless fields whose linear perturbations leave the ten-dimensional background metric unperturbed, as well as the minimally-coupled massive scalar. We find that various fields have the same absorption probability as that of the dilaton-axion system, which is given exactly via the Mathieu equation. We analyze the features of the absorption cross-sections in terms of effective Schr\"odinger potentials, conjecture a general form of the dual effective potentials, and provide explicit numerical results for the whole energy range. As expected, all partial-wave absorption probabilities tend to zero (one) at low (large) energies, and exhibit an oscillatory pattern as a function of energy. The equivalence of absorption probabilities for various modes has implications for the correlation functions on the field, including subleading contributions on the field-theory side. In particular, certain half-integer and integer spin fields have identical absorption probabilities, thus providing evidence that the corresponding operator pairs on the field theory side belong to the same supermultiplets.Comment: Latex, 9 figures and 17 page

Using particle shape to induce tilted and bistable liquid crystal anchoring

We use Monte Carlo simulations of hard Gaussian overlap (HGO) particles symmetrically confined in slab geometry to investigate the role of particle-substrate interactions on liquid crystalline anchoring. Despite the restriction here to purely steric interactions and smooth substrates, a range of behaviours are captured, including tilted anchoring and homeotropic-planar bistability. These macroscopic behaviours are all achieved through appropriate tuning of the microscopics of the HGO-substrate interaction, based upon non-additive descriptions for the HGO-substrate shape parameter.</p