Effective interactions from q-deformed inspired transformations

From the mass term for the transformed quark fields, we obtain effective contact interactions of the NJL type. The parameters of the model that maps a system of non-interacting transformed fields into quarks interacting via NJL contact terms are discussed

On the q-deformation of the NJL model

Using a q-deformed fermionic algebra we perform explicitly a deformation of the Nambu-Jona-Lasinio (NJL) Hamiltonian. In the Bogoliubov-Valatin approach we obtain the deformed version of the functional for the total energy, which is minimized to obtain the corresponding gap equation. The breaking of chiral symmetry and its restoration in the limit $q \to 0$ are then discussed.Comment: 5 eps figure

Accessing the Acceleration of the Universe with Sunyaev-Zel'dovich and X-ray Data from Galaxy Clusters

By using exclusively the Sunyaev-Zel'dovich effect and X-ray surface brightness data from 25 galaxy clusters in the redshift range 0.023< z < 0.784 we access cosmic acceleration employing a kinematic description. Such result is fully independent on the validity of any metric gravity theory, the possible matter-energy contents filling the Universe, as well as on the SNe Ia Hubble diagram.Comment: 3 pages, 4 figures, To appear in the Proceedings of the Twelfth Marcel Grossmann Meeting on General Relativit

Are Galaxy Clusters Suggesting an Accelerating Universe?

The present cosmic accelerating stage is discussed through a new kinematic method based on the Sunyaev- Zel'dovich effect (SZE) and X-ray surface brightness data from galaxy clusters. By using the SZE/X-ray data from 38 galaxy clusters in the redshift range $0.14 \leq z \leq 0.89$ [Bonamente et al., Astrop. J. {\bf 647}, 25 (2006)] it is found that the present Universe is accelerating and that the transition from an earlier decelerating to a late time accelerating regime is relatively recent. The ability of the ongoing Planck satellite mission to obtain tighter constraints on the expansion history through SZE/X-ray angular diameters is also discussed. Our results are fully independent on the validity of any metric gravity theory, the possible matter- energy contents filling the Universe, as well as on the SNe Ia Hubble diagram from which the presenting accelerating stage was inferred.Comment: 6 pages, 6 figures, AIP Conf. Proc. Invisible Universe: Proceedings of the Conferenc

On the algebraic Bethe ansatz: Periodic boundary conditions

In this paper, the algebraic Bethe ansatz with periodic boundary conditions is used to investigate trigonometric vertex models associated with the fundamental representations of the non-exceptional Lie algebras. This formulation allow us to present explicit expressions for the eigenvectors and eigenvalues of the respective transfer matrices.Comment: 36 pages, LaTex, Minor Revisio

Clustering, Angular Size and Dark Energy

The influence of dark matter inhomogeneities on the angular size-redshift test is investigated for a large class of flat cosmological models driven by dark energy plus a cold dark matter component (XCDM model). The results are presented in two steps. First, the mass inhomogeneities are modeled by a generalized Zeldovich-Kantowski-Dyer-Roeder (ZKDR) distance which is characterized by a smoothness parameter $\alpha(z)$ and a power index $\gamma$, and, second, we provide a statistical analysis to angular size data for a large sample of milliarcsecond compact radio sources. As a general result, we have found that the $\alpha$ parameter is totally unconstrained by this sample of angular diameter data.Comment: 9 pages, 7 figures, accepted in Physical Review

Physical approximations for the nonlinear evolution of perturbations in dark energy scenarios

The abundance and distribution of collapsed objects such as galaxy clusters will become an important tool to investigate the nature of dark energy and dark matter. Number counts of very massive objects are sensitive not only to the equation of state of dark energy, which parametrizes the smooth component of its pressure, but also to the sound speed of dark energy as well, which determines the amount of pressure in inhomogeneous and collapsed structures. Since the evolution of these structures must be followed well into the nonlinear regime, and a fully relativistic framework for this regime does not exist yet, we compare two approximate schemes: the widely used spherical collapse model, and the pseudo-Newtonian approach. We show that both approximation schemes convey identical equations for the density contrast, when the pressure perturbation of dark energy is parametrized in terms of an effective sound speed. We also make a comparison of these approximate approaches to general relativity in the linearized regime, which lends some support to the approximations.Comment: 15 pages, 2 figure

Brane World Dynamics and Adiabatic Matter creation

We have treated the adiabatic matter creation process in various three-brane models by applying thermodynamics of open systems. The matter creation rate is found to affect the evolution of scale factor and energy density of the universe. We find modification at early stages of cosmic dynamics. In GB and RS brane worlds, by chosing appropriate parameters we obtain standard scenario, while the warped DGP model has different Friedmann equations. During later stages, since the matter creation is negligible the evolution reduces to FRW expansion, in RS and GB models.Comment: Replaced with TEX file,No figures, Corrected References and typos. Accepted in IJMP