Search

We study gravity models in the language of scalar-tensor (ST) theories. The correspondence between gravity and ST theories is revisited since gravity is a subclass of Brans-Dicke models, with a vanishing coupling constant (). In this treatment, four toy models are used to analyze the early-universe cosmology, when the scalar field dominates over standard matter. We have obtained solutions to the Klein-Gordon equation for those models. It is found that for the first model , as time increases the scalar field decreases and decays asymptotically. For the second model , it was found that the function crosses the -axis at different values for different values of . For the third model , when the value of is small, the potential behaves like the standard inflationary potential. For the fourth model , we show that there is a transition between . The behavior of the potentials with is totally different from those with . The slow-roll approximation is applied to each of the four models and we obtain the respective expressions for the spectral index and the tensor-to-scalar ratio . [ABSTRACT FROM AUTHOR]

We consider a nonlinear sigma-model-like theory of bulk scalar fields coupled to the five-dimensional Einstein gravity. In Robertson-Walker spacetimes, we find some power-law cosmological solutions for the scale factor when the expansion rate of an extra dimension is proportional to one of our (3+1)-dimensional universe. Among them, the solution with a decreasing warp factor could be related to the one-brane model of Randall and Sundrum. [ABSTRACT FROM AUTHOR]

We compute the cosmological constant in a scale invariant scalar field theory. The gravitational action is also suitably modified to respect scale invariance. Due to scale invariance, the theory does not admit a cosmological constant term. The scale invariance is broken by a recently introduced mechanism called cosmological symmetry breaking. This leads to a nonzero cosmological constant. We compute the one-loop corrections to the cosmological constant and show that it is finite. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study braneworld cosmologies in the presence of stringy corrections coupled to a canonical scalar field. Two independent models are explored which in their own right provide cosmologies exhibiting the present cosmic acceleration of the universe. The evolution of the cosmological scale factor is studied in four and ten-dimensional space–times. The four-dimensional model is preformed in the context of the nonminimal Maxwell–Gauss–Bonnet gravity while the ten-dimensional model is constructed from the implications of Kaluza–Klein cosmology together with the Gauss–Bonnet Lagrangian in the action with matter fields nonminimally coupled to gravity. Both the low energy and high energy limits are discussed for the two models and many interesting features are described in some detail. [ABSTRACT FROM AUTHOR]