27,841 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
Galaxy rotation curves from General Relativity with Renormalization Group corrections
We consider the application of quantum corrections computed using
renormalization group arguments in the astrophysical domain and show that, for
the most natural interpretation of the renormalization group scale parameter, a
gravitational coupling parameter varying of its value across a
galaxy (which is roughly a variation of per light-year) is
sufficient to generate galaxy rotation curves in agreement with the
observations. The quality of the resulting fit is similar to the Isothermal
profile quality once both the shape of the rotation curve and the mass-to-light
ratios are considered for evaluation. In order to perform the analysis, we use
recent high quality data from nine regular disk galaxies. For the sake of
comparison, the same set of data is modeled also for the Modified Newtonian
Dynamics (MOND) and for the recently proposed Scalar Tensor Vector Gravity
(STVG). At face value, the model based on quantum corrections clearly leads to
better fits than these two alternative theories.Comment: 35 pages, 12 PDF figures. v4: Version accepted in JCAP. Improved
comments on the galactic gas effects to our model, stressed the relevance of
our MOND and STVG fits, slightly extended discussion on our perspectives and
minor additional comments. Ref's added
On duality of the noncommutative extension of the Maxwell-Chern-Simons model
We study issues of duality in 3D field theory models over a canonical
noncommutative spacetime and obtain the noncommutative extension of the
Self-Dual model induced by the Seiberg-Witten map. We apply the dual projection
technique to uncover some properties of the noncommutative Maxwell-Chern-Simons
theory up to first-order in the noncommutative parameter. A duality between
this theory and a model similar to the ordinary self-dual model is
estabilished. The correspondence of the basic fields is obtained and the
equivalence of algebras and equations of motion are directly verified. We also
comment on previous results in this subject.Comment: Revtex, 9 pages, accepted for publication PL
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)
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
The Quantum Algebraic Structure of the Twisted XXZ Chain
We consider the Quantum Inverse Scattering Method with a new R-matrix
depending on two parameters and . We find that the underlying algebraic
structure is the two-parameter deformed algebra enlarged by
introducing an element belonging to the centre. The corresponding Hamiltonian
describes the spin-1/2 XXZ model with twisted periodic boundary conditions.Comment: LateX file, 9 pages, Minor changes (including authors` names in the
hep-th heading
Terrain Database Correlation Assessment Using an Open Source Tool
Configuring networked simulators for training military teams in a distributed
environment requires the usage of a set of terrain databases to represent the
same training area. The results of simulation exercises can be degraded if the
terrain databases are poorly correlated. A number of methodologies for
determining the correlation between terrain databaHowever, there are few
computational tools for this task and most of them were developed to address
government needs, have limited availability, and handle specific digital
formats. The goal of this paper is thus to present a novel open source tool
developed as part of an academic research project.Comment: 12 pages, I/ITSEC 201
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