Related papers: Brans-Dicke Cosmology Corrected for a Quantum Effe…
We propose a gravitational model with a Brans-Dicke-type scalar field having, in the would-be action, a "wrong-sign" kinetic term and a quartic interaction term. In a cosmological context, we obtain, depending on the boundary conditions,…
We find a static solution for the scale-factor in a Brans-Dicke generalized theory where the scalar field and the coupling constant vary with time. We find also that in the early Universe there may be amplification of gravitational waves.
We study the Brans-Dicke model in the presence of an axion. The dynamical equations are solved when the fields are space independent and the metric is spatially flat. It is found that at late time the scale factor undergoes decelerated…
The loop quantization of Brans-Dicke theory (with coupling parameter $\omega\neq-3/2$) is studied. In the geometry-dynamical formalism, the canonical structure and constraint algebra of this theory are similar to those of general relativity…
We consider an extended scalar-tensor theory of gravity where the action has two interacting scalar fields, a Brans-Dicke field which makes the effective Newtonian constant a function of coordinates and a Higgs field which has derivative…
We show that Brans-Dicke (BD) theory in 5D may explain the present cosmic accelerated expansion without recurring to matter fields in 5D or dark energy in 4D. Without making any assumption on the nature of the extra coordinate or the matter…
Time-dependent scalar fields provide a candidate explanation for the dark energy. For these to vary on cosmological time scales, the derivative of the scalar potential in Planck units should have roughly the same magnitude as the potential…
We present a brief review of the modified Brans-Dicke theory (MBDT) in arbitrary dimensions, whereby the ($N+1$)-dimensional field equations reduce to the $N$-dimensional $(ND)$ configuration with sources and an effective induced scalar…
A five-dimensional solution to Einstein's equations coupled to a scalar field has been proposed as a partial solution to the cosmological constant problem: the effect of arbitrary vacuum energy (tension) of a 3-brane is cancelled; however,…
An analysis of the solutions for the field equations of generalized scalar-tensor theories of gravitation is performed through the study of the geometry of the phase space and the stability of the solutions, with special interest in the…
The dynamics of the Brans-Dicke theory with a scalar field potential function is investigated. We show that the system with a barotropic matter content can be reduced to an autonomous three-dimensional dynamical system. For an arbitrary…
We study the cosmology of the Brans-Dicke(BD) theory coupled to perfect fluid type matter. In our previous works, the case where matter is coming from the Ramond-Ramond sector of the string theory was studied. Here, we study the case where…
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 $\omega$ by considering the quantum back reaction…
To inherit more features of full loop quantum Brans-Dicke theory, the Euclidean and Lorentzian terms of the Hamiltonian constraint are quantized independently in loop quantum Brans-Dicke cosmology. An alternative Hamiltonian constraint…
Brane worlds are theories with extra spatial dimensions in which ordinary matter is localized on a (3+1) dimensional submanifold. Such theories could have interesting consequences for particle physics and gravitational physics. In this…
Quantum effects play an essential role in modern cosmology. Perhaps the most striking example comes from large-scale structures, generally assumed to originate from vacuum quantum fluctuations and stretched by an expansion phase. Inflation…
We study the classical and quantum cosmology of a universe in which the matter source is a massive Dirac spinor field and consider cases where such fields are either free or self-interacting. We focus attention on the spatially flat…
Scalar field models with non-standard kinetic terms have been proposed in the context of k-inflation, of Born-Infeld lagrangians, of phantom energy and, more in general, of low-energy string theory. In general, scalar fields are expected to…
It has long been demonstrated that the vacuum scalar-tensor theory in the Jordan-frame Brans-Dicke parametrization is form-invariant under conformal transformations, provided that a suitable transformation of the coupling parameter $\omega$…
Given that the simple wave equation of Brans-Dicke theory for the scalar field is preserved, we have investigated, through exhaustively analyzing the Bianchi identities, the consistent theories which violate the exact energy conservation…