UC Research Repository Collection:http://hdl.handle.net/10092/242014-04-13T03:09:32Z2014-04-13T03:09:32ZCosmic acceleration from M theory on twisted spacesNeupane, I.P.Wiltshire, D.L.http://hdl.handle.net/10092/90452014-04-02T11:37:25Z2005-01-01T00:00:00ZTitle: Cosmic acceleration from M theory on twisted spaces
Authors: Neupane, I.P.; Wiltshire, D.L.
Abstract: In a recent paper [I. P. Neupane and D. L. Wiltshire, Phys. Lett. B 619, 201 (2005).] we have found a new class of accelerating cosmologies arising from a time-dependent compactification of classical supergravity on product spaces that include one or more geometric twists along with nontrivial curved internal spaces. With such effects, a scalar potential can have a local minimum with positive vacuum energy. The existence of such a minimum generically predicts a period of accelerated expansion in the four-dimensional Einstein conformal frame. Here we extend our knowledge of these cosmological solutions by presenting new examples and discuss the properties of the solutions in a more general setting. We also relate the known (asymptotic) solutions for multiscalar fields with exponential potentials to the accelerating solutions arising from simple (or twisted) product spaces for internal manifolds.
Description: doi: 10.1103/PhysRevD.72.0835092005-01-01T00:00:00ZAccelerating cosmologies from compactification with a twistNeupane, I.P.Wiltshire, D.L.http://hdl.handle.net/10092/90432014-04-02T11:36:55Z2005-01-01T00:00:00ZTitle: Accelerating cosmologies from compactification with a twist
Authors: Neupane, I.P.; Wiltshire, D.L.
Abstract: It is demonstrated by explicit solutions of the 4+n–dimensional vacuum Einstein equations that
accelerating cosmologies in the Einstein conformal frame can be obtained by a time–dependent compactification
of string/M–theory, even in the case that internal dimensions are Ricci–flat, provided
one includes one or more geometric twists. Such acceleration is transient. When both compact
hyperbolic internal spaces and geometric twists are included, however, the period of accelerated
expansion may be made arbitrarily large.
Description: DOI: 10.1016/j.physletb.2005.06.0082005-01-01T00:00:00ZSuper p-branesAchúcarro, A.Evans, J.M.Townsend, P.K.Wiltshire, D.L.http://hdl.handle.net/10092/90412014-04-02T11:36:24Z1987-01-01T00:00:00ZTitle: Super p-branes
Authors: Achúcarro, A.; Evans, J.M.; Townsend, P.K.; Wiltshire, D.L.
Abstract: It is shown that the extension of the spacetime supersymmetric Green-
Schwarz covariant superstring action to p-dimensional extended objects (p-branes) is possible if and only if the on-shell p-dimensional bose and fermi
degrees of freedom are equal. This is further evidence for world-tube supersymmetry
in these models. All the p-brane models are related to superstring
actions in d = 3, 4, 6 or 10 dimensions by double dimensional reduction, (which
we generalise to reduction on arbitrary compact spaces), and we also show how
they may be considered as topological defects of supergravity theories.1987-01-01T00:00:00ZCosmological equivalence principle and the weak-field limitWiltshire, D.L.http://hdl.handle.net/10092/90402014-04-02T11:35:54Z2008-01-01T00:00:00ZTitle: Cosmological equivalence principle and the weak-field limit
Authors: Wiltshire, D.L.
Abstract: The strong equivalence principle is extended in application to averaged dynamical fields in cosmology to include the role of the average density in the determination of inertial frames. The resulting cosmological equivalence principle is applied to the problem of synchronization of clocks in the observed universe. Once density perturbations grow to give density contrasts of order 1 on scales of tens of megaparsecs, the integrated deceleration of the local background regions of voids relative to galaxies must be accounted for in the relative synchronization of clocks of ideal observers who measure an isotropic cosmic microwave background. The relative deceleration of the background can be expected to represent a scale in which weak-field Newtonian dynamics should be modified to account for dynamical gradients in the Ricci scalar curvature of space. This acceleration scale is estimated using the best-fit nonlinear bubble model of the universe with backreaction. At redshifts z<~0.25 the scale is found to coincide with the empirical acceleration scale of modified Newtonian dynamics. At larger redshifts the scale varies in a manner which is likely to be important for understanding dynamics of galaxy clusters, and structure formation. Although the relative deceleration, typically of order 10⁻¹⁰ms⁻², is small, when integrated over the lifetime of the universe it amounts to an accumulated relative difference of 38% in the rate of average clocks in galaxies as compared to volume-average clocks in the emptiness of voids. A number of foundational aspects of the cosmological equivalence principle are also discussed, including its relation to Mach's principle, the Weyl curvature hypothesis, and the initial conditions of the universe.2008-01-01T00:00:00Z