Curved dilatonic brane-worlds and the cosmological constant problem

We construct a model for dilatonic brane worlds with constant curvature on the brane, i.e. a non-zero four-dimensional cosmological constant, given in function of the dilaton coupling and the cosmological constant of the bulk. We compare this family of solutions to other known dilatonic domain wall solutions and apply a self-tunning mechanism to check the stability of our solutions under quantum fluctuations living on the brane.Comment: latex, 6 pages. (v2): considerable changes in the conclusion. (v3): added new discussion on the solutions and some references; version to appear in CQ

The Near-Horizon Limit of the Extreme Rotating d=5 Black Hole as a Homogenous Spacetime

We show that the spacetime of the near-horizon limit of the extreme rotating d=5 black hole, which is maximally supersymmetric in N=2,d=5 supergravity for any value of the rotation parameter j in [-1,1], is locally isomorphic to a homogeneous non-symmetric spacetime corresponding to an element of the 1-parameter family of coset spaces SO(2,1)x SO(3)/SO(2)_j in which the subgroup SO(2)_j is a combination of the two SO(2) subgroups of SO(2,1) and SO(3).Comment: Some points clarified and misprints corrected. Version to be published in Classical and Quantum Gravit

E11 and Spheric Vacuum Solutions of Eleven- and Ten dimensional Supergravity Theories

In view of the newly conjectured Kac-Moody symmetries of supergravity theories placed in eleven and ten dimensions, the relation between these symmetry groups and possible compactifications are examined. In particular, we identify the relevant group cosets that parametrise the vacuum solutions of AdS x S type.Comment: discussion improve

Central Charge for AdS_2 Quantum Gravity

Two-dimensional Maxwell-dilaton quantum gravity on AdS_2 with radius $\ell$ and a constant electric field E is studied. In conformal gauge, this is equivalent to a CFT on a strip. In order to maintain consistent boundary conditions, the usual conformal diffeomorphisms must be accompanied by a certain U(1) gauge transformation. The resulting conformal transformations are generated by a twisted stress tensor, which has a central charge $c={3k E^2 \ell^4/4}$ where k is the level of the U(1) current. This is an AdS_2 analog of the Brown-Henneaux formula $c = 3\ell/2G$ for the central charge of quantum gravity on AdS_3

Wrapped M2/M5 Duality

A microscopic accounting of the entropy of a generic 5D supersymmetric rotating black hole, arising from wrapped M2-branes in Calabi-Yau compactified M-theory, is an outstanding unsolved problem. In this paper we consider an expansion around the zero-entropy, zero-temperature, maximally rotating ground state for which the angular momentum J_L and graviphoton charge Q are related by J_L^2=Q^3. At J_L=0 the near horizon geometry is AdS_2 x S^3. As J_L^2 goes to Q^3 it becomes a singular quotient of AdS_3 x S^2: more precisely, a quotient of the near horizon geometry of an M5 wrapped on a 4-cycle whose self-intersection is the 2-cycle associated to the wrapped-M2 black hole. The singularity of the AdS_3 quotient is identified as the usual one associated to the zero-temperature limit, suggesting that the (0,4) wrapped-M5 CFT is dual near maximality to the wrapped-M2 black hole. As evidence for this, the microscopic (0,4) CFT entropy and the macroscopic rotating black hole entropy are found to agree to leading order away from maximality.Comment: 10 pages, no figure

Higher Dimensional Taub-NUTs and Taub-Bolts in Einstein-Maxwell Gravity

We present a class of higher dimensional solutions to Einstein-Maxwell equations in d-dimensions. These solutions are asymptotically locally flat, de-Sitter, or anti-de Sitter space-times. The solutions we obtained depend on two extra parameters other than the mass and the nut charge. These two parameters are the electric charge, q and the electric potential at infinity, V, which has a non-trivial contribution. We Analyze the conditions one can impose to obtain Taub-Nut or Taub-Bolt space-times, including the four-dimensional case. We found that in the nut case these conditions coincide with that coming from the regularity of the one-form potential at the horizon. Furthermore, the mass parameter for the higher dimensional solutions depends on the nut charge and the electric charge or the potential at infinity.Comment: 11 pages, LaTe

Compactifications with S-Duality Twists

We consider generalised Scherk Schwarz reductions of supergravity and superstring theories with twists by electromagnetic dualities that are symmetries of the equations of motion but not of the action, such as the S-duality of D=4, N=4 super-Yang-Mills coupled to supergravity. The reduction cannot be done on the action itself, but must be done either on the field equations or on a duality invariant form of the action, such as one in the doubled formalism in which potentials are introduced for both electric and magnetic fields. The resulting theory in odd-dimensions has massive form fields satisfying a self-duality condition $dA \sim m*A$. We construct such theories in D=3,5,7.Comment: Latex, 26 pages. References adde

Kaehler forms and cosmological solutions in type II supergravities

We consider cosmological solutions to type II supergravity theories where the spacetime is split into a FRW universe and a K\"ahler space, which may be taken to be Calabi-Yau. The various 2-forms present in the theories are taken to be proportional to the K\"ahler form associated to the K\"ahler space.Comment: 6 pages, LaTeX2