Particle theory

Abstract:

Precision measurements of anisotropies in the cosmic microwave background and of the clustering of largescale structure have supposedly confirmed that the primordial density perturbation has a (nearly) scale-invariant spectrum. However this conclusion is based on assumptions about the world model and the nature of the dark matter. Physical models of inflation suggest that the spectrum may not in fact be scale-free, which would imply rather different cosmological parameters on the basis of the same observational data.

Abstract:

We study the effective D=4, N=1 supergravity description of five-dimensional heterotic M theory in the presence of an M5 brane, and derive the Killing vectors and isometry group for the Kähler moduli-space metric. The group is found to be a non-semi-simple maximal parabolic subgroup of Sp(4,R), containing a nontrivial SL(2,R) factor. The underlying moduli space is then naturally realized as the group space Sp(4,R)/U(2), but equipped with a nonhomogeneous metric that is invariant only under that maximal parabolic group. This nonhomogeneous metric space can also be derived via field truncations and identifications performed on Sp(8,R)/U(4) with its standard homogeneous metric. In a companion paper we use these symmetries to derive new cosmological solutions from known ones. © 2005 The American Physical Society.

Abstract:

Quasinormal frequencies of electromagnetic and gravitational perturbations in asymptotically anti-de Sitter spacetime can be identified with poles of the corresponding real-time Green's functions in a holographically dual finite temperature field theory. The quasinormal modes are defined for gauge-invariant quantities which obey an incoming-wave boundary condition at the horizon and a Dirichlet condition at the boundary. As an application, we explicitly find poles of retarded correlation functions of R-symmetry currents and the energy-momentum tensor in strongly coupled finite temperature N=4 supersymmetric SU(Nc) Yang-Mills theory in the limit of large Nc. © 2005 The American Physical Society.