jueves, 2 de agosto de 2012

2 de agosto de 2012

1208.0021 Observational Constraints on Nfields Phantom Power-Law

IftikharAhmad , Farah Naz. Institute of Physics and Mathematical Sciences,
Department of Mathematics, University of Gujrat. Gujrat, Pakistan.

Abstract: In the multi-fields Phantom power law we investigate the analytical behavior of many scalar fields working collectively, where 'i is the ith scalar field. Furthermore, we evaluate its parameter values by applying certain constraints on our model parameters, and then compare these values with current observational data from Observational data of CMB, BAO and H0. Through our results, we deeply observe that in the dark-energy EOS parameter at the Big Rip always finite with the pressure and dark energy density divergence.
Keywords: phantom power-law Cosmology, multi-fields.

1208.0025 Stability of a non-minimally conformally coupled scalar field in F(T )cosmology

Mubasher Jamil,1, 2, ∗ D. Momeni,2, † and Ratbay Myrzakulov2, ‡
1Center for Advanced Mathematics and Physics (CAMP), National University of Sciences and Technology (NUST), H-12, Islamabad, Pakistan
2Eurasian International Center for Theoretical Physics,
L.N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan

Abstract: In this paper, we introduce a non-minimally conformally coupled scalar field and dark matter in F(T ) cosmology and study their dynamics. We investigate the stability and phase space behavior of the parameters of the scalar field by choosing an exponential potential and cosmologically viable form of F(T ). We found that the dynamical system of equations admit two unstable critical points, thus no attractor solutions exist in this cosmology. Furthermore taking into account the scalar field mimicking as quintessence and phantom energy, we discuss the corresponding cosmic evolution for both small and large times. We investigate the cosmological implications of the model via equation of state and deceleration parameters of our model and show that the late time Universe will be dominated by phantom energy and moreover phantom crossing is possible. Our results have no explicit predictions for inflation and early Universe era.

Keywords: Cosmology; torsion; stability; scalar fields; quintessence; phantom energy.
PACS numbers: 04.20.Fy; 04.50.+h; 98.80.-k

Eur. Phys. J. C (2012) 72:2075

1208.00615 Quintom phase-space: beyond the exponential potential
Genly Leon. Departamento de Matemática, Universidad Central de Las Villas, C. P. 53840, Santa Clara, Cuba and Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4950, Valparaíso, Chile.
Yoelsy Leyva† and J. Socorro‡. Departamento de Física, DCI, Universidad de Guanajuato-Campus León, C.P. 37150, Le´on, Guanajuato, México.

Abstract: We investigate the phase-space structure of the quintom dark energy paradigm in the framework of spatially flat and homogeneous universe. Considering arbitrary decoupled potentials, we find certain general conditions under which the the phantom dominated solution is late time attractor, generalizing previous results found for the case of exponential potential. Center Manifold Theory is employed to obtain sufficient conditions for the instability of de Sitter solution either with phantom or quintessence potential dominance. Another important issue is concerning the existence of a point corresponding to the standard quintessence dominated solution, which under certain condition on the potential, can mimic the dark matter behavior. This feature has important cosmological consequences to address de unified description of dark matter and dark energy in a single field.

1208.00103 Galileon Black Holes
Massimiliano Rinaldi. Namur Center for Complex systems (naXys), University of Namur, Belgium

Abstract: We study the spherically symmetric solutions to the gravitational field equations with a derivative coupling to a massless scalar field. This configuration is motivated by Galileon gravity as it preserves shift invariance in the scalar sector. We obtain exact black hole solutions that are similar to asymptotically de Sitter or anti-de Sitter black holes, according to the sign of the coupling constant
of the Galileon term. We examine the spacetime structure and the thermodynamical properties of these solutions, and we reveal the non-perturbative nature of the coupling constant. We find a phase transition, similar to the one described by Hawking and Page, which occurs at a critical temperature determined by both the black hole mass and by the strength of the coupling.

No hay comentarios:

Publicar un comentario