Lensing by gravitational waves in scalar-tensor gravity: Einstein frame analysis

The amplification of a light beam due to intervening gravitational waves is studied. The previous Jordan frame result according to which the amplification is many orders of magnitude larger in scalar-tensor gravity than in general relativity does not hold in the Einstein conformal frame. Lensing by gravitational waves is discussed in relation to the ongoing and proposed VLBI observations aimed at detecting the scintillation effect.Comment: 12 pages, LaTeX, to appear in Astronomy & Astrophysic

Tales of tails in cosmology

Late time mild inflation (LTMI) proposes to solve the age of the universe problem and the discrepancy between locally and globally measured values of the Hubble parameter. However, the mechanism proposed to achieve LTMI is found to be physically pathological by applying the theory of tails for the solutions of wave equations in curved spaces. Alternative mechanisms for LTMI are discussed, and the relevance of scalar wave tails for cosmology is emphasized.Comment: 16 pages, LaTeX, no figures, to apper in Int. J. Mod. Phys.

Inflationary cosmology with two-component fluid and thermodynamics

We present a simple and self-consistent cosmology with a phenomenological model of quantum creation of radiation and matter due to decay of the cosmological constant $\Lambda$. The decay drives a non-isentropic inflationary epoch, which exits smoothly to the radiation-dominated era, without reheating, and then evolves to the dust era. The initial vacuum for radiation and matter is a regular Minkowski vacuum. The created radiation and matter obeys standard thermodynamic laws, and the total entropy produced is consistent with the accepted value. This paper is an extension of the model with the decaying cosmological constant considered previously. We compare our model with the quantum field theory approach to creation of particles in curved space.Comment: 16 pages Late

Stochastic Conservation Laws?

We examine conservation laws, typically the conservation of linear momentum, in the light of a recent successful formulation of fermions as Kerr-Newman type Black Holes, which are created fluctuationally from a background Zero Point Field. We conclude that these conservation laws are to be taken in the spirit of thermodynamic laws.Comment: 5 pages, Te

Superinflation, quintessence, and nonsingular cosmologies

The dynamics of a universe dominated by a self-interacting nonminimally coupled scalar field are considered. The structure of the phase space and complete phase portraits are given. New dynamical behaviors include superinflation ($\dot{H}>0$), avoidance of big bang singularities through classical birth of the universe, and spontaneous entry into and exit from inflation. This model is promising for describing quintessence as a nonminimally coupled scalar field.Comment: 4 pages, 2 figure

A note on dualities in Einstein's gravity in the presence of a non-minimally coupled scalar field

We show that the action of Einstein's gravity with a scalar field coupled in a generic way to spacetime curvature is invariant under a particular set of conformal transformations. These transformations relate dual theories for which the effective couplings of the theory are scaled uniformly. In the simplest case, this class of dualities reduce to the S-duality of low-energy effective action of string theory.Comment: 12 page

On the stability of gravity in the presence of a non-minimally coupled scalar field

We show that Einstein's gravity coupled to a non-minimally coupled scalar field is stable even for high values of the scalar field, when the sign of the Einstein-Hilbert action is reversed. We also discuss inflationary solutions and a possible new mechanism of reheating.Comment: References and some clarifications added; 11 pages, 1 figure; submitted to Physics Letters