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Montiel A.,Research Center Estudios Avanzados Del | Breton N.,Research Center Estudios Avanzados Del | Salzano V.,University of the Basque Country
General Relativity and Gravitation | Year: 2014

The cosmological model consisting of a nonlinear magnetic field obeying the Lagrangian L= γ Fα being the electromagnetic invariant, coupled to a Robertson-Walker geometry is tested with observational data of Type Ia Supernovae, Long Gamma-Ray Bursts and Hubble parameter measurements. The statistical analysis show that the inclusion of nonlinear electromagnetic matter is enough to produce the observed accelerated expansion, with not need of including a dark energy component. The electromagnetic matter with abundance ΩB, gives as best fit from the combination of all observational data sets Ω B=0.562+0.037 -0.038 for the scenario in which α =-1, ΩB=0.654+0.040 -0.040 for the scenario with α =-1/4 and ΩB=0.683+0.039 -0.043 for the one with α =-1/8. These results indicate that nonlinear electromagnetic matter could play the role of dark energy, with the theoretical advantage of being a mensurable field. © 2014 Springer Science+Business Media New York.

Lazkoz R.,University of the Basque Country | Montiel A.,Research Center Estudios Avanzados Del | Salzano V.,University of the Basque Country
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

In this paper we set observational constraints of the superfluid Chaplygin gas model, which gives a unified description of the dark sector of the Universe as a Bose-Einstein condensate that behaves as dark energy while it is in the ground state and as dark matter when it is in the excited state. We first show and perform the various steps leading to a form of the equations suitable for the observational tests to be carried out. Then, by using a Markov Chain MonteCarlo code, we constrain the model with a sample of cosmology-independent long gamma-ray bursts calibrated using their type I fundamental plane, as well as the Union2.1 set and observational Hubble parameter data. In this analysis, using our cosmological constraints, we sketch the effective equation of state parameter and the deceleration parameter, and we also obtain the redshift of the transition from deceleration to acceleration z t. © 2012 American Physical Society.

Montiel A.,Research Center Estudios Avanzados Del | Lazkoz R.,University of the Basque Country | Sendra I.,University of the Basque Country | Escamilla-Rivera C.,University of the Basque Country | Salzano V.,University of the Basque Country
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

In this work we present a nonparametric approach, which works on minimal assumptions, to reconstruct the cosmic expansion of the Universe. We propose to combine a locally weighted scatterplot smoothing method and a simulation-extrapolation method. The first one (LOESS) is a nonparametric approach that allows us to obtain smoothed curves with no prior knowledge of the functional relationship between variables or of the cosmological quantities. The second one (SIMEX) takes into account the effect of measurement errors on a variable via a simulation process. For the reconstructions we use as raw data the Union2.1 type Ia supernovae compilation, as well as recent Hubble parameter measurements. This work aims to illustrate the approach, which turns out to be a self-sufficient technique in the sense that we do not have to choose anything by hand. We examine the details of the method, among them the amount of observational data needed to perform the locally weighted fit which will define the robustness of our reconstruction. In view of our results, we believe that our proposal offers a promising alternative for reconstructing global trends of cosmological data when there is little intuition on the relationship between the variables and we also think it even presents good prospects to generate reliable mock data points where the original sample is poor. © 2014 American Physical Society.

Velten H.,Bielefeld University | Montiel A.,Research Center Estudios Avanzados Del | Carneiro S.,Federal University of Bahia
Monthly Notices of the Royal Astronomical Society | Year: 2013

In previous papers, a cosmological model with constant rate particle creation and vacuum term decaying linearly with the Hubble parameter was shown to lead to a good concordance when tested against precise observations: the position of the first peak in the spectrum of anisotropies of the cosmic microwave background (CMB), the Hubble diagram for Type Ia supernovae (SNe Ia), the distribution of large-scale structures and the distance to the baryonic acoustic oscillations (BAO). That model has the same number of parameters as the spatially flat standard model and seems to alleviate some observational/theoretical tensions appearing in the latter. In this paper, we complement those tests with 109 gamma-ray bursts (GRBs), 59 of them with redshifts above z = 1.4, which permits to extend the Hubble diagram to redshifts up to z ≈ 8. For the calibration of the 50 GRBs with z < 1.4, we use the 288 supernovae of the Sloan Digital Sky Survey project, calibrated with the MLCS2k2 fitter, less model-dependent than other samples like Union2. Our results show a good concordance with the previous tests and, again, less tensions between SNe Ia and GRB best fits as compared to the standard model. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Breton N.,Research Center Estudios Avanzados Del | Bergliaffa S.E.P.,State University of Rio de Janeiro
Annals of Physics | Year: 2015

We analyze the thermodynamical stability of static and spherically symmetric black hole solutions with nonlinear electromagnetism as a source, and show that any sequence of such black holes in isolation that includes the Schwarzschild black hole is stable in the (βM, M) plane for any nonlinear Lagrangian describing the electromagnetic field. The study of three exact solutions (which include the Schwarzschild solution in some limit) in the (βQ, Q) plane show that they are stable in the microcanonical ensemble, and unstable or less unstable (due to the existence of a turning point) in the canonical ensemble. If the less unstable configurations are stable, our results indicate that they would be in equilibrium with a reservoir at a higher temperature than the corresponding Reissner-Nordstrom configuration. An expression for the heat capacity at constant charge valid for any Lagrangian describing nonlinear electromagnetism is also presented. It displays a divergence with a change of sign that occurs precisely at the turning point obtained by the Poincarè method. © 2015 Elsevier Inc.

Manko V.S.,Research Center Estudios Avanzados Del | Ruiz E.,University of Salamanca
Progress of Theoretical and Experimental Physics | Year: 2013

The Kerr-Newman solution with negative mass is shown to develop a massless ring singularity off the symmetry axis. The singularity is located inside the region with closed timelike curves which has the topology of a torus and lies outside the ergoregion. These characteristics are also shared by the charged Tomimatsu-Sato δ = 2 solution with negative total mass to which in particular a simple form in terms of four polynomials is provided. © The Author(s) 2013.

Suarez A.,Research Center Estudios Avanzados Del | Robles V.H.,Research Center Estudios Avanzados Del | Matos T.,Research Center Estudios Avanzados Del
Astrophysics and Space Science Proceedings | Year: 2014

We review the work done so far aimed at modeling in an alternative way the dark matter in the Universe: the scalar field Bose-Einstein condensate dark matter (SFDM/BEC) model.We discuss a number of important achievements and characteristics of the model.We also describe some of our most recent results and predictions of the model compared to those of the standard model of ΛCDM. © Springer International Publishing Switzerland 2014.

Breton N.,Research Center Estudios Avanzados Del | Montiel A.,Research Center Estudios Avanzados Del
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The luminosity distance describing the effect of local inhomogeneities in the propagation of light proposed by Zeldovich, Kantowski, Dyer, and Roeder is tested with two probes for two distinct ranges of redshifts: supernovae Ia in 0.015≤z≤1.414 and gamma-ray bursts in 1.547≤z≤3.57. Our analysis is performed by a Markov chain Monte Carlo code that allows us to constrain the matter density parameter Ωm as well as the smoothness parameter α that measures the inhomogeneous-homogeneous rate of the cosmic fluid in a flat Λ cold dark matter model. The obtained best fits are Ωm=0.285-0.018+0.019, α=0.856-0.176+0.106 from supernovae Ia, and Ωm=0.259-0.028+0.028, α=0.587-0.202+0.201 from gamma-ray bursts, while from the joint analysis the best fits are Ωm=0.284-0.020+0.021, α=0.685-0.171+0.164 with χred2=0.975. The value of the smoothness parameter α indicates a clumped universe; however, it does not have an impact on the amount of dark energy (cosmological constant) needed to fit the observations. This result may be an indication that the Dyer-Roeder approximation does not describe in a precise form the effects of clumpiness in the expansion of the Universe. © 2013 American Physical Society.

Montiel A.,Research Center Estudios Avanzados Del | Breton N.,Research Center Estudios Avanzados Del
Journal of Cosmology and Astroparticle Physics | Year: 2011

In this paper we extend the range of consistency of a constant bulk viscosity model to redshifts up to z ∼ 8.1. In this model the dark sector of the cosmic substratum is a viscous fluid with pressure p = -ζθ, where θ is the fluid-expansion scalar and ζ is the coefficient of bulk viscosity. Using the sample of 59 high-redshift GRBs reported by Wei (2010), we calibrate GRBs at low redshifts with the Union 2 sample of SNe Ia, thus avoiding the circularity problem. Testing the constant bulk viscosity model with GRBs we found the best fit for the viscosity parameter in the range 0 < < 3, so that it be consistent with previous probes; we also determined the deceleration parameter q0 and the redshift of transition to accelerated expansion. Besides, we present an updated analysis of the model with CMB5-year data and CMB7-year data, as well as with the baryon acoustic peak BAO. From the statistics with CMB it turns out that the model does not describe in a feasible way to such a far epoch of recombination of the universe, but is in very good concordance for epochs as far as z ∼ 8.1 till present. © 2011 IOP Publishing Ltd and SISSA.

Torres Martinez D.Y.,CINVESTAV | Castanedo Perez R.,CINVESTAV | Torres Delgado G.,CINVESTAV | Zelaya Angel O.,Research Center Estudios Avanzados Del
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2012

Thin films of the mixed ZnO-SnO 2 system were obtained by employing the sol-gel technique, starting from the mixture of zinc oxide and tin oxide precursor solutions. The tin atomic concentration percentages (X) in the precursor solutions with respect to the ZnO + SnO 2 total growing solution were: 0, 10, 20, 30, 40 and 100 at.%, here, the ZnO atomic percentage is (100-X). The films were deposited by the dip coating method on glass substrates and were sintered at 450, 500 and 550 °C, in an open atmosphere. The X-ray diffraction patterns show the presence of zinc oxide and tin oxide crystals. The optical properties of the films were studied by UV-vis spectroscopy. The photocatalytic activity was quantified by means of the bleaching of methylene blue. The films of the mixed ZnO-SnO 2 system show higher photocatalytic activity than the SnO 2 and ZnO films. © 2012 Elsevier B.V.

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