4 research outputs found
f(R) theories of gravity in Palatini approach matched with observations
We investigate the viability of f(R) theories in the framework of the
Palatini approach as solutions to the problem of the observed accelerated
expansion of the universe. Two physically motivated popular choices for f(R)
are considered: power law, f(R) = \beta R^n, and logarithmic, f(R) = \alpha
\ln{R}. Under the Palatini approach, both Lagrangians give rise to cosmological
models comprising only standard matter and undergoing a present phase of
accelerated expansion. We use the Hubble diagram of type Ia Supernovae and the
data on the gas mass fraction in relaxed galaxy clusters to see whether these
models are able to reproduce what is observed and to constrain their
parameters. It turns out that they are indeed able to fit the data with values
of the Hubble constant and of the matter density parameter in agreement with
some model independent estimates, but the today deceleration parameter is
higher than what is measured in the concordance LambdaCDM model.Comment: 14 pages, 8 figures, submitted to Physical Review
One-loop f(R) gravity in de Sitter universe
Motivated by the dark energy issue, the one-loop quantization approach for a
family of relativistic cosmological theories is discussed in some detail.
Specifically, general gravity at the one-loop level in a de Sitter
universe is investigated, extending a similar program developed for the case of
pure Einstein gravity. Using generalized zeta regularization, the one-loop
effective action is explicitly obtained off-shell, what allows to study in
detail the possibility of (de)stabilization of the de Sitter background by
quantum effects. The one-loop effective action maybe useful also for the study
of constant curvature black hole nucleation rate and it provides the plausible
way of resolving the cosmological constant problem.Comment: 25 pages, Latex file. Discussion enlarged, new references added.
Version accepted in JCA