Soft inflation

The cosmology resulting from two coupled scalar fields was studied, one which is either a new inflation or chaotic type inflation, and the other which has an exponentially decaying potential. Such a potential may appear in the conformally transformed frame of generalized Einstein theories like the Jordan-Brans-Dicke theory. The constraints necessary for successful inflation are examined. Conventional GUT models such as SU(5) were found to be compatible with new inflation, while restrictions on the self-coupling constant are significantly loosened for chaotic inflation

Extended Inflation with a Curvature-Coupled Inflaton

We examine extended inflation models enhanced by the addition of a coupling between the inflaton field and the space-time curvature. We examine two types of model, where the underlying inflaton potential takes on second-order and first-order form respectively. One aim is to provide models which satisfy the solar system constraints on the Brans--Dicke parameter $\omega$. This constraint has proven very problematic in previous extended inflation models, and we find circumstances where it can be successfully evaded, though the constraint must be carefully assessed in our model and can be much stronger than the usual $\omega > 500$. In the simplest versions of the model, one may avoid the need to introduce a mass for the Brans--Dicke field in order to ensure that it takes on the correct value at the present epoch, as seems to be required in hyperextended inflation. We also briefly discuss aspects of the formation of topological defects in the inflaton field itself.Comment: 24 pages, LaTeX (no figures), to appear, Physical Review D, mishandling of the solar system constraint on extended gravity theories corrected, SUSSEX-AST 93/6-

Coleman-Weinberg Symmetry Breaking in a Bianchi I Universe

The one-loop effective potential for a massive, quartically self- interacting scalar field nonminimally coupled to gravity is calculated in a Bianchi I universe with small anisotropy. The kernel of a Schrodinger-like equation is found, and its coincidence limit used to obtain the determinant of the Klein-Gordon operator. The effects of the anisotropy on symmetry breaking and the viability of new inflation are considered, with the value of the coupling to gravity ¸ found to play a crucial role. Classically, a positive ¸ restores symmetry and helps inflation, while opposite effects are found for negative coupling. Quantum effects depend on the value of ¸ relative to the conformal value 1/6. For small coupling, the quantum term may dominate, which tends to restore symmetry and aid inflation. Comparison to previous work is made, and differences discussed. February, 1992 (*) Current address: Jet Propulsion Laboratory, 4800 Oak Grove Drive, M/S 183-501, Pasadena, CA 91109. Email: berkin@kra..

Multiple Field Scalar-Tensor Theories of Gravity and Cosmology

We consider multiple scalar fields coupled to gravity, with special attention given to two-field theories. First, the conditions necessary for these theories to exactly meet solar system tests are given. We find, in particular, that these constraints require that some scalar kinetic terms be non-positive-definite. Next, we investigate the cosmological evolution of the fields to see if these conditions can be met. Solutions are found in the dust era, as well as radiation and cosmological constant dominated epochs. The possibility of inflation in these theories is discussed. While power law growth of the scalar fields can yield the appropriate conditions to meet solar system constraints, these solutions are unstable. October, 1993 (*) Email: [email protected] (**) Email: [email protected] 1 Introduction Scalar-tensor (ST) theories are alternative models of gravity which provide a theoretical framework within which general relativity (GR) may be tested. Many important test..

PAST STUDIES....................................................................................... 6

LOSS HARVESTING AND HIFO...............................................................

3-Form Induced Potentials, Dilaton Stabilization, and Running Moduli

We study the potential induced by imaginary self-dual 3-forms in compactifications of string theory and the cosmological evolution associated with it. The potential contains exponentials of the volume moduli of the compactification, and we demonstrate that the exponential form of the potential leads to a power law for the scale factor of the universe. This power law does not support accelerated expansion. We explain this result in terms of supersymmetry and comment on corrections to the potential that could lead to inflation or quintessence