107 research outputs found
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
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 where k is the level of the U(1) current. This is an AdS_2 analog of
the Brown-Henneaux formula 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 . 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
- âŠ