arXiv subjects

Monica Capone

Publications and source records attributed to Monica Capone.

4 recordsLinked to original sources

arXiv2012

Spiral galaxies rotation curves in the Horava - Lifshitz gravity theory

We focus on a modified version of Horava - Lifschitz theory and, in particular, we consider the impact of its weak - field static spherically symmetric limit on the galaxy dynamics. In a previous paper, we used the modified gravitational potential obtained in this theory to evaluate the Milky Way rotation curve using a spheroidal truncated power - law bulge and a double exponential disc as the only sources of the gravitational field and showed that the modified rotation curved is not in agreement with the data. Making a step forward, we here include also the contribution from a dark matter halo in order to see whether this helps fitting the rotation curve data. As a test case, we consider a sample of spiral galaxies with smooth baryon matter distribution and well measured circular velocity profiles. It turns out that, although a marginal agreement with the data can be found, this can only be obtained if the dark matter halo has an unrealistically small virial mass and incredibly large concentration. Such results can be interpreted as a strong evidence against the reliability of the gravitational potential obtained in the modified version of Horava -Lifschitz theory that we consider.

astro-ph.CO↗

arXiv2010

Accelerating cosmology in Rastall's theory

In an attempt to look for a viable mechanism leading to a present-day accelerated expansion, we investigate the possibility that the observed cosmic speed up may be recovered in the framework of the Rastall's theory, relying on the non-conservativity of the stress-energy tensor, i.e. $T^μ_{ν; μ} \neq 0$. We derive the modified Friedmann equations and show that they correspond to Cardassian-like equations. We also show that, under suitable assumptions on the equation of state of the matter term sourcing the gravitational field, it is indeed possible to get an accelerated expansion, in agreement with the Hubble diagram of both Type Ia Supernovae (SNeIa) and Gamma Ray Bursts (GRBs). Unfortunately, to achieve such a result one has to postulate a matter density parameter much larger than the typical $Ω_M \simeq 0.3$ value inferred from cluster gas mass fraction data.

astro-ph.CO↗

arXiv2010

Jumping from Metric f(R) to Scalar-Tensor Theories and the relations between their post-Newtonian Parameters

We review the dynamical equivalence between $f(R)$ gravity in the metric formalism and scalar-tensor gravity, and use this equivalence to deduce the post-Newtonian parameters $γ$ and $β$ for a $f(R)$ theory, obtaining a result that is different with respect to that known in the literature. Then, we obtain explicit expressions of these paremeters in terms of the mass of the scalar field (or, differently speaking, the mass of the additional scalar degree of freedom associated to a $f(R)$ theory) which can be used to constrain $f(R)$ gravity by means of current observations.

gr-qc↗

arXiv2004

Conformal aspects of Palatini approach in Extended Theories of Gravity

The debate on the physical relevance of conformal transformations can be faced by taking the Palatini approach into account to gravitational theories. We show that conformal transformations are not only a mathematical tool to disentangle gravitational and matter degrees of freedom (passing from the Jordan frame to the Einstein frame) but they acquire a physical meaning considering the bi-metric structure of Palatini approach which allows to distinguish between spacetime structure and geodesic structure. Examples of higher-order and non-minimally coupled theories are worked out and relevant cosmological solutions in Einstein frame and Jordan frames are discussed showing that also the interpretation of cosmological observations can drastically change depending on the adopted frame.

hep-th↗