10 research outputs found
Scaling Cosmologies from Duality Twisted Compactifications
Oscillating moduli fields can support a cosmological scaling solution in the
presence of a perfect fluid when the scalar field potential satisfies
appropriate conditions. We examine when such conditions arise in
higher-dimensional, non-linear sigma-models that are reduced to four dimensions
under a generalized Scherk-Schwarz compactification. We show explicitly that
scaling behaviour is possible when the higher-dimensional action exhibits a
global SL(n,R) or O(2,2) symmetry. These underlying symmetries can be exploited
to generate non-trivial scaling solutions when the moduli fields have
non-canonical kinetic energy. We also consider the compactification of
eleven-dimensional vacuum Einstein gravity on an elliptic twisted torus.Comment: 21 pages, 3 figure
Generating Geodesic Flows and Supergravity Solutions
We consider the geodesic motion on the symmetric moduli spaces that arise
after timelike and spacelike reductions of supergravity theories. The geodesics
correspond to timelike respectively spacelike -brane solutions when they are
lifted over a -dimensional flat space. In particular, we consider the
problem of constructing \emph{the minimal generating solution}: A geodesic with
the minimal number of free parameters such that all other geodesics are
generated through isometries. We give an intrinsic characterization of this
solution in a wide class of orbits for various supergravities in different
dimensions. We apply our method to three cases: (i) Einstein vacuum solutions,
(ii) extreme and non-extreme D=4 black holes in N=8 supergravity and their
relation to N=2 STU black holes and (iii) Euclidean wormholes in . In
case (iii) we present an easy and general criterium for the existence of
regular wormholes for a given scalar coset.Comment: Fixed a typo in table 3, page 27, results unchange
Geodesic Flows in Cosmology
In this brief note we discuss geodesic flows that correspond to cosmological solutions in higher-dimensional supergravity. On the one hand, we explain that S-brane solutions are in one-to-one correspondence with geodesic curves on the moduli space through dimensional reduction over the brane worldvolume. On the other hand, reduction over the transversal space gives rise to a scalar potential for the moduli and the geodesic motion is deformed. Nonetheless, in most cases, the scalar flow becomes geodesic asymptotically in which case the solution is described by a multi-field scaling cosmology.
Generating Geodesic Flows and Supergravity Solutions
We consider the geodesic motion on the symmetric moduli spaces that arise after timelike and spacellike reductions of supergravity theories. The geodesics correspond to timelike respectively spacelike p-brane Solutions when they are lifted over a p-dimensional flat space. In particular, we consider the problem of constructing the minimal generating solution: A geodesic with the minimal number of free parameters such that all other geodesics are generated through isometrics. We give an intrinsic characterization of this solution in a wide class of orbits for various supergravities in different dimensions. We apply our method to three cases: (i) Einstein vacuum solutions, (ii) extreme and non-extreme D = 4 black holes in N = 8 supergravity and their relation to N = 2 STU black holes and (iii) Euclidean wormholes in D >= 3. In case (iii) we present an easy and general criterium for the existence of regular wormholes for a given scalar coset