arXiv subjects

Sante Carloni

Publications and source records attributed to Sante Carloni.

80 records · Page 5Linked to original sources

arXiv2007

An analysis of the shear dynamics in Bianchi I cosmologies with $R^n$-gravity

We consider the case of $R^n$-gravity and perform a detailed analysis of the dynamics in Bianchi I cosmologies which exhibit {\it local rotational symmetry} (LRS). We find exact solutions and study their behaviour and stability in terms of the values of the parameter $n$. In particular, we found a set of cosmic histories in which the universe is initially isotropic, then develops shear anisotropies which approaches a constant value.

gr-qc↗

arXiv2006

The evolution of tensor perturbations in scalar-tensor theories of gravity

The evolution equations for tensor perturbations in a generic scalar tensor theory of gravity are presented. Exact solution are given for a specific class of theories and Friedmann-Lemaître-Robertson-Walker backgrounds. In these cases it is shown that, although the evolution of tensor models depends on the choice of parameters of the theory, no amplification is possible if the gravitational interaction is attractive.

gr-qc↗

arXiv2006

A dynamical system approach to higher order gravity

The dynamical system approach has recently acquired great importance in the investigation on higher order theories of gravity. In this talk I review the main results and I give brief comments on the perspectives for further developments.

gr-qc↗

arXiv2006

Gauge invariant perturbations of Scalar-Tensor Cosmologies: The vacuum case

The covariant gauge invariant perturbation theory of scalar cosmological perturbations is developed for a general Scalar-Tensor Friedmann-Lemaitre-Robertson-Walker cosmology in a vacuum. The perturbation equations are then solved exactly in the long wavelength limit for a specific coupling, potential and background. Differences with the minimally coupled case are briefly discussed.

gr-qc↗

arXiv2006

Shear dynamics in Bianchi I cosmologies with R^n-gravity

We give the equations governing the shear evolution in Bianchi spacetimes for general f(R)-theories of gravity. We consider the case of R^n-gravity and perform a detailed analysis of the dynamics in Bianchi I cosmologies which exhibit local rotational symmetry. We find exact solutions and study their behaviour and stability in terms of the values of the parameter n. In particular, we found a set of cosmic histories in which the universe is initially isotropic, then develops shear anisotropies which approaches a constant value.

gr-qc↗

arXiv2005

Bounce Conditions in f(R) Cosmologies

We investigate the conditions for a bounce to occur in Friedmann-Robertson-Walker cosmologies for the class of fourth order gravity theories. The general bounce criterion is determined and constraints on the parameters of three specific models are given in order to obtain bounces solutions. It is found that unlike the case of General Relativity, a bounce appears to be possible in open and flat cosmologies.

gr-qc↗

arXiv2004

Neutrino mixing as a source for cosmological constant

We report on recent results showing that neutrino mixing may lead to a non-zero contribution to the cosmological constant. This contribution is of a completely different nature with respect to the usual one by a massive spinor field. We also study the problem of field mixing in Quantum Field Theory in curved space-time, for the case of a scalar field in the Friedmann-Robertson-Walker metric.

hep-th↗

arXiv2004

Neutrino mixing and cosmological constant

We report on the recent result that the non--perturbative vacuum structure associated with neutrino mixing leads to a non--zero contribution to the value of the cosmological constant. Its value is estimated by using the natural cut--off appearing in the quantum field theory formalism for neutrino mixing.

hep-th↗