2,802 research outputs found
Disk and elliptical galaxies within renormalization group improved gravity
The paper is about possible effects of infrared quantum contributions to
General Relativity on disk and elliptical galaxies. The Renormalization Group
corrected General Relativity (RGGR model) is used to parametrize these quantum
effects. The new RGGR results presented here concern the elliptical galaxy NGC
4374 and the dwarf disk galaxy DDO 47. Using the effective approach to Quantum
Field Theory in curved background, one can argue that the proper RG energy
scale, in the weak field limit, should be related to the Newtonian potential.
In the context of galaxies, this led to a remarkably small variation of the
gravitational coupling G, while also capable of generating galaxy rotation and
dispersion curves of similar quality to the the best dark matter profiles
(i.e., the profiles that have a core).Comment: 5 pages. This paper is based on a talk given by D.C. Rodrigues at the
I CosmoSul meeting (Rio de Janeiro, RJ - Brazil. August, 01-05, 2011). To be
published in AIP conference Proceeding
Vacuum effective action and inflation
We consider vacuum quantum effects in the Early Universe, which may lead to
inflation. The inflation is a direct consequence of the supposition that, at
high energies, all the particles can be described by the weakly interacting,
massless, conformally invariant fields. We discuss, from the effective field
theory point of view, the stability of inflation, transition to the FRW
solution, and also possibility to study metric and density perturbations.Comment: 6 pages, LaTeX, no figures. Contribution to the Proceedings of the X
Jorge Andre Swieca school in Particles and Fields. To be published in World
Scientifi
Modified gravity models and the central cusp of dark matter haloes in galaxies
The N-body dark matter (DM) simulations point that DM density profiles, e.g. the Navarro Frenk White (NFW) halo, should be cuspy in its centre, but observations disfavour this kind of DM profile. Here we consider whether the observed rotation curves close to the galactic centre can favour modified gravity models in comparison to the NFW halo, and how to quantify such difference. Two explicit modified gravity models are considered, Modified Newtonian Dynamics (MOND) and a more recent approach renormalization group effects in general relativity (RGGR). It is also the purpose of this work to significantly extend the sample on which RGGR has been tested in comparison to other approaches. By analysing 62 galaxies from five samples, we find that (i) there is a radius, given by half the disc scale length, below which RGGR and MOND can match the data about as well or better than NFW, albeit the formers have fewer free parameters; (ii) considering the complete rotation curve data, RGGR could achieve fits with better agreement than MOND, and almost as good as a NFW halo with two free parameters (NFW and RGGR have, respectively, two and one more free parameters than MOND)
Perturbative analysis of generalized Einstein's theories
The hypothesis that the energy-momentum tensor of ordinary matter is not
conserved separately, leads to a non-adiabatic expansion and, in many cases, to
an Universe older than usual. This may provide a solution for the entropy and
age problems of the Standard Cosmological Model. We consider two different
theories of this type, and we perform a perturbative analysis, leading to
analytical expressions for the evolution of gravitational waves, rotational
modes and density perturbations. One of these theories exhibits satisfactory
properties at this level, while the other one should be discarded.Comment: 14 pages, Latex fil
Renormalization Group approach to Gravity: the running of G and L inside galaxies and additional details on the elliptical NGC 4494
We explore the phenomenology of nontrivial quantum effects on low-energy
gravity. These effects come from the running of the gravitational coupling
parameter G and the cosmological constant L in the Einstein-Hilbert action, as
induced by the Renormalization Group (RG). The Renormalization Group corrected
General Relativity (RGGR model) is used to parametrize these quantum effects,
and it is assumed that the dominant dark matter-like effects inside galaxies is
due to these nontrivial RG effects. Here we present additional details on the
RGGR model application, in particular on the Poisson equation extension that
defines the effective potential, also we re-analyse the ordinary elliptical
galaxy NGC 4494 using a slightly different model for its baryonic contribution,
and explicit solutions are presented for the running of G and L. The values of
the NGC 4494 parameters as shown here have a better agreement with the general
RGGR picture for galaxies, and suggest a larger radial anisotropy than the
previously published result.Comment: 9 pages, 2 figs. Based on a talk presented at the VIII International
Workshop on the Dark Side of the Universe, June 10-15, 2012, Buzios, RJ,
Brazil. v2: typos removed, matches published versio
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