Luis O. Pimentel

New Exact Vacuum Solutions in Brans–Dicke Theory

A family of exact solutions to vacuum Brans–Dicke theory with spherical symmetry is found. In the limit of large ω this family reduces to the solutions obtained in general relativity with a scalar field. The solutions show curvature singularities for all times, therefore they do not represent the gravitational collapse of a physical system with regular initial data in the theory. One would like to interpret it as an inhomogeneous dynamical cosmology, but the lack of a regular spacelike slice forbids it. For a special value of an integration constant we have an isotropic cosmological model without the problems mentioned above.

Exact solutions in Brans-Dicke theory with bulk viscosity

The effect of bulk viscosity on the evolution of the homogeneous and isotropic cosmological models in the Brans-Dicke theory of gravitation is studied. Solutions are found, with a baratropic equation of state, a time-independent bulk viscosity, the gravitational “constant” inversely proportional to the age of the universe, and the mass of the universe (in the closed model) proportional to the square of its age; the expansion factor is a linear function of the cosmological time. For flat space, power law expansions are found, among them one that is related to extended inflation.

Exact self-creation cosmological solutions

Under the assumption of a power law between the expansion factor of the Universe and the scalar field of the second self-creation theory proposed by G. A. Barber, the cosmological equations are reduces to quadratures. Several exact solutions are obtained, among them linearly expanding and inflationary universes with a barotropic equation of state.

Noncommutative quantum cosmology

We consider noncommutative quantum cosmology in the case of the low-energy string effective theory. Exact solutions are found and compared with the commutative case.

Exact cosmological solutions in the scalar-tensor theory with cosmological constant

Under the assumption of a power-law between the expansion factor of the Universe, and the scalar field (πan=c=const.) tensor theory with cosmological constant are reduced to quadrature. Several exact solutions are obtained, among them inflationary universes that have barotropic equation of state.

Exact cosmological solution with particle creation in JBD theory

Exact solutions are sought by taking the generated particles of spin 1/2 (according to the creation rate of Schäfer and Dehnen [1]) as matter sources of the Cosmological equations of JBD theory. There exists one exact solution for which the “gravitational constant” decreases linearly with time and the mass of the universe increases proportionally to the square of its age (Diracs hypotheses). The radius of curvature increases linearly with time while the density decreases inversely with it. It is found that for an age of the universe ≃ 10−22 sec only two particles have populated the universe. This is assumed to be the initial state of the model. The calculated present particle number and their density are in agreement with the observed data. This model implies that all present matter (excluding the two initial particles) has been created by the expansion of the universe.

Cosmological models with dynamical Lambda in scalar tensor theories

In the context of a family of scalar-tensor theories with a dynamical

Third quantization of Brans–Dicke cosmology

\ensuremath{\Lambda}

REQUIRED CONDITIONS FOR LATE TIME ACCELERATION AND EARLY TIME DECELERATION IN GENERALIZED SCALAR–TENSOR THEORIES

that is a binomial on the scalar field, the cosmological equations are considered. A general baryotropic state equation

Gravitational potential of a point mass in a brane world

p=(\ensuremath{\gamma}\ensuremath{-}1)\ensuremath{\rho},