arXiv subjects

D. Nunez

Publications and source records attributed to D. Nunez.

7 recordsLinked to original sources

arXiv2007

Constraints on mSUGRA through entropy and abundance criteria

We derive an expression for the entropy of a present dark matter halo described by a Navarro-Frenk-White modified model with a central core. The comparison of this entropy with the one of the halo at the freeze-out era allows us to obtain an expression for the relic abundance of neutralinos, which in turn is used to constrain the parameter space in mSUGRA models, when used with the WMAP observations. Moreover, by joning these results with the ones obtained from the usual abundance criteria, we are able to clearly discriminate validity regions among tan beta values of the mSUGRA model, by demanding both criteria to be consistent with the 2 sigma bounds of the WMAP observations for the relic density: 0.112 < Omega h^2 < 0.122. We found that for sign mu positive, small values of tan beta are not favored; only for tan beta ~ 50 are both criteria significantly consistent. The use of both criteria also allows us to put a lower bound on the neutralino mass of > 151 GeV.

astro-ph↗

arXiv2001

Scalar Field Dark Matter

This work is a review of the last results of research on the Scalar Field Dark Matter model of the Universe at cosmological and at galactic level. We present the complete solution to the scalar field cosmological scenario in which the dark matter is modeled by a scalar field $Φ$ with the scalar potential $V(Φ)=V_{0}(cosh {(λ\sqrt{κ_{0}}Φ)}-1)$ and the dark energy is modeled by a scalar field $Ψ$, endowed with the scalar potential $\tilde{V}(Ψ)= \tilde{V_{0}}(\sinh{(α\sqrt{κ_{0}}Ψ)})^β$, which together compose the 95% of the total matter energy in the Universe. The model presents successfully deals with the up to date cosmological observations, and is a good candidate to treat the dark matter problem at the galactic level.

astro-ph↗

arXiv2000

Spherical Scalar Field Halo in Galaxies

We study a spherically symmetric fluctuation of scalar dark matter in the cosmos and show that it could be the dark matter in galaxies, provided that the scalar field has an exponential potential whose overall sign is negative and whose exponent is constrained observationally by the rotation velocities of galaxies. The local space-time of the fluctuation contains a three dimensional space-like hypersurface with surplus of angle.

astro-ph↗

arXiv1994

Dynamics of Massive Shells Ejected in a Supernova Explosion

An expanding shell is accelerated outward by radiation from the remnant star and slowed by ram pressure and accretion as it plows into the interstellar medium. We set up the general relativistic equations of motion for such a shell. In the non-relativistic limit, the reduce to the standard Ostriker-Gunn equations. Furthermore, it is shown that the motion equation can be integrated in general, reducing in this way the study of the dynamics of a shell to a set of four coupled first order differential equations, solvable up to quadrature

astro-ph↗

arXiv1993

Stationary Axisymmetric Fields as Two-Dimensional Geodesics

Einstein's equations for stationary axisymmetric fields are reformulated as the equations for affine geodesics in a two--dimensional space. The affine collineations of this space are investigated and used to relate explicit solutions of Einstein's equations with different physical properties. Particularly, the solutions describing the exterior fields of a dyon and a slowly rotating body are discussed.

gr-qc↗

arXiv1993

Dynamics and Collision of Massive Shells in Curved Backgrounds

We analyse the dynamics of the collision of two spherical massive shells in a generally spherically symmetric background, obtaining an expression from the conservation law that imposes a constraint between the different parameters involved. We study the light-like limit and make some comparisons of the predictions of our master equation with the results obtained in the case of collision of light-like shells, like the short life of white holes or the mass inflation phenomena. We present some particular cases of the constraint equation.

gr-qc↗

arXiv1992

Cauchy horizon singularity without mass inflation

A perturbed Reissner-Nordström-de Sitter solution is used to emphasize the nature of the singularity along the Cauchy horizon of a charged spherically symmetric black hole. For these solutions, conditions may prevail under which the mass function is bounded and yet the curvature scalar $R_{αβγδ} R^{αβγδ}$ diverges.

gr-qc↗