The Ups and Downs of Cyclic Universes (2007)
We investigate homogeneous and isotropic oscillating cosmologies with multiple fluid components. Transfer of energy between these fluids is included in order to model the effects of non-equilibrium...
Islands in the landscape (2007)
Clifton, T., Linde, Andrei, Sivanandam, Navin
The string theory landscape consists of many metastable de Sitter vacua, populated by eternal inflation. Tunneling between these vacua gives rise to a dynamical system, which asymptotically settles...
Alternative Theories of Gravity (2006)
This work investigates alternative theories of gravity, the solutions to their field equations and the constraints that can be imposed upon them from observation and experiment. Specifically, we...
Alternative Theories of Gravity (2006)
This work investigates alternative theories of gravity, the solutions to their field equations and the constraints that can be imposed upon them from observation and experiment. Specifically, we...
Spherically Symmetric Solutions to Fourth-Order Theories of Gravity (2006)
Gravitational theories generated from Lagrangians of the form f(R) are considered. The spherically symmetric solutions to these equations are discussed, paying particular attention to features that...
Cosmologies with Energy Exchange (2006)
We provide a simple mathematical description of the exchange of energy between two fluids in an expanding Friedmann universe with zero spatial curvature. The evolution can be reduced to a single...
We consider the possibility of energy being exchanged between the scalar and matter fields in scalar-tensor theories of gravity. Such an exchange provides a new mechanism which can drive variations...
Further Exact Cosmological Solutions to Higher-Order Gravity Theories (2006)
We investigate the effect of deviations from general relativity on approach to the initial singularity by finding exact cosmological solutions to a wide class of fourth-order gravity theories. We...
The Existence of Godel, Einstein and de Sitter Universes (2005)
We determine the general conditions for the existence of Godel, Einstein static, and de Sitter universes in gravity theories derived from a Lagrangian that is an arbitrary function of the scalar...
Exact cosmological solutions of scale-invariant gravity theories (2005)
We have found new anisotropic vacuum solutions for the scale-invariant gravity theories which generalise Einstein's general relativity to a theory derived from the Lagrangian $R^{1+\delta}$. These...
Constraints on the Variation of G from Primordial Nucleosynthesis (2005)
Clifton, T., Barrow, J. D., Scherrer, R. J.
We study here the effect of a varying G on the evolution of the early Universe and, in particular, on primordial nucleosynthesis. This variation of G is modelled using the Brans-Dicke theory as well...
Clifton, T., Mota, D. F., Barrow, J. D.
We study the inhomogeneous cosmological evolution of the Newtonian gravitational 'constant' G in the framework of scalar-tensor theories. We investigate the differences that arise between the...