Cosmological implications of a light dilaton

Supersymmetric Peccei-Quinn symmetry and string theory predict a complex scalar field comprising a dilaton and an axion. These fields are massless at high energies, but it is known since long that the axion is stabilized in an instanton dominated vacuum. Instantons and axions together also provide a mechanism to stabilize a dilaton, thus accounting for a dilaton as a possible cold dark matter component accompanying the axion. We briefly review the prospects of this scenario and point out further implications.Comment: LaTeX, 9 pages incl. 1 figure, reference adde

Induced inflation from a 5D purely kinetic scalar field formalism on warped product spaces

Considering a separable and purely kinetic 5D scalar field on a warped product metric background we propose a new and more general approach for inducing 4D scalar potentials on a 4D constant foliation of the 5D space-time. We obtain an induced potential for a true 4D scalar field instead of a potential for an effective 4D scalar field. In this formalism we can recover the usual 4D inflationary formalism with a geometrically induced inflationary potential. In addition the quantum confinement of the inflaton modes is obtained naturally from the model for at least a class of warping factors. Besides the 4D inflationary physics that results of this formalism is independent of the 4D-hypersurface chosen.Comment: 8 pages Accepted for publication in European Physical Journal

Cosmic Microwave Background Anisotropy with Cosine-Type Quintessence

We study the Cosmic Microwave Background (CMB) anisotropies produced by cosine-type quintessence models. In our analysis, effects of the adiabatic and isocurvature fluctuations are both taken into account. For purely adiabatic fluctuations with scale invariant spectrum, we obtain a stringent constraint on the model parameters using the CMB data from COBE, BOOMERanG and MAXIMA. Furthermore, it is shown that isocurvature fluctuations have significant effects on the CMB angular power spectrum at low multipoles in some parameter space, which may be detectable in future satellite experiments. Such a signal may be used to test the cosine-type quintessence models.Comment: 21 pages, 9 figure

Acceleration of the universe, vacuum metamorphosis, and the large-time asymptotic form of the heat kernel

We investigate the possibility that the late acceleration observed in the rate of expansion of the universe is due to vacuum quantum effects arising in curved spacetime. The theoretical basis of the vacuum cold dark matter (VCDM), or vacuum metamorphosis, cosmological model of Parker and Raval is revisited and improved. We show, by means of a manifestly nonperturbative approach, how the infrared behavior of the propagator (related to the large-time asymptotic form of the heat kernel) of a free scalar field in curved spacetime causes the vacuum expectation value of its energy-momentum tensor to exhibit a resonance effect when the scalar curvature R of the spacetime reaches a particular value related to the mass of the field. we show that the back reaction caused by this resonance drives the universe through a transition to an accelerating expansion phase, very much in the same way as originally proposed by Parker and Raval. Our analysis includes higher derivatives that were neglected in the earlier analysis, and takes into account the possible runaway solutions that can follow from these higher-derivative terms. We find that the runaway solutions do not occur if the universe was described by the usual classical FRW solution prior to the growth of vacuum energy-density and negative pressure (i.e., vacuum metamorphosis) that causes the transition to an accelerating expansion of the universe in this theory.Comment: 33 pages, 3 figures. Submitted to Physical Review D15 (Dec 23, 2003). v2: 1 reference added. No other change