We consider two-dimensional Brans-Dicke theory to study the initial singularity problem. It turns out that the initial curvature singularity can be finite for a certain Brans-Dicke constant ω by considering the quantum back reaction of the geometry. For ω = 1, the universe starts with the finite curvature scalar and evolves into the flat spacetime. Furthermore the divergent gravitational coupli...

We consider two-dimensional Brans-Dicke theory to study the initial singularity problem. It turns out that the initial curvature singularity can be finite for a certain Brans-Dicke constant ω by considering the quantum back reaction of the geometry. For ω = 1, the universe starts with the finite curvature scalar and evolves into the flat spacetime. Furthermore the divergent gravitational coupli...

We study the effect of the solitonic degree of freedom in string cosmology following the line of Rama. The gas of solitonic p-brane is treated as a perfect fluid in a Brans-Dicke type theory. In this paper, we find exact cosmological solutions for any Brans-Dicke parameter ω and for general parameter γ of equation of state and classify the the cosmology of the solutions according to the paramet...

Inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold M = M 0 × n i=1 M i (n ≥ 1) are investigated under dimensional reduction to a D 0-dimensional effective non-minimally coupled σ-model which generalizes the familiar Brans-Dicke model. It is argued that the Einstein frame should be considered as the physical one. The general prescription for the Eins...

We study the dynamics of false vacuum bubbles in the Brans-Dicke theory of gravity by using the thin shell or thin wall approximation. We consider a false vacuum bubble that has a different value for the Brans-Dicke field between the inside false vacuum region and the outside true vacuum region. Within a certain limit of field values, the difference of field values makes the effective tension o...

We investigate the stability of a family of spherically symmetric static solutions in vacuum Brans-Dicke theory ~with v50) recently described by van Putten. Using linear perturbation theory, we find one exponentially growing mode for every member of the family of solutions, and thus conclude that the solutions are not stable. Using a previously constructed code for spherically symmetric Brans-D...

The bounded orbital motion of a massive spinless test particle in the background of a Kerr Brans-Dicke geometry is analysed in terms of worldlines that are auto-parallels of different metric compatible spacetime connections. In one case the connection is that of Levi-Civita with zero-torsion. In the second case the connection has torsion determined by the gradient of the Brans-Dicke background ...

We argue that the geodesic hypothesis based on auto-parallels of the Levi-Civita connection may need refinement in theories of gravity with additional scalar fields. This argument is illustrated with a reformulation of the Brans-Dicke theory in terms of a spacetime connection with torsion determined dynamically in terms of the gradient of the Brans-Dicke scalar field. The perihelion shift in th...

The qualitative properties of spatially homogeneous stiff perfect fluid and minimally coupled massless scalar field models within general relativity are discussed. Consequently, by exploiting the formal equivalence under conformal transformations and field redefinitions of certain classes of theories of gravity, the asymptotic properties of spatially homogeneous models in a class of scalar-tens...

We present the static, spherically symmetric solutions of the low energy d = 4 string. They form a simple generalisation of the Schwarzschild solution and describe the gravitational field of a spherical star in perturbative string theory. If the Robertson parameter γ is different from one, these solutions describe singular objects with naked singularities at their horizons, and whose Hawking te...