Publications (78)122.22 Total impact
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ABSTRACT: We study electric and magnetic monopoles in static, spherically symmetric and constant curvature geometries in the context of the inverse electrodynamics model. We prove that this U(1) invariant Lagrangian density is able to support the standard metric of a ReissnerNordstrom Black Hole, but with more complex thermodynamical properties than in the standard case. By employing the Euclidean Action approach we perform a complete analysis of its phase space depending on the sign and singularities of the heat capacity and the Helmholtz free energy.07/2014; 
Article: The largescale structure of vacuum
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ABSTRACT: The vacuum state in quantum field theory is known to exhibit an important number of fundamental physical features. In this work we explore the possibility that this state could also present a nontrivial spacetime structure on large scales. In particular, we will show that by imposing the renormalized vacuum energymomentum tensor to be conserved and compatible with cosmological observations, the vacuum energy of sufficiently heavy fields behaves at late times as nonrelativistic matter rather than as a cosmological constant. In this limit, the vacuum state supports perturbations whose speed of sound is negligible and accordingly allows the growth of structures in the vacuum energy itself. This largescale structure of vacuum could seed the formation of galaxies and clusters very much in the same way as cold dark matter does.05/2014; 
Article: Vacuum energy as dark matter
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ABSTRACT: We consider the vacuum energy of massive quantum fields in an expanding universe. We define a conserved renormalized energymomentum tensor by means of a comoving cutoff regularization. Using exact solutions for de Sitter spacetime, we show that in a certain range of mass and renormalization scales there is a contribution to the vacuum energy density that scales as nonrelativistic matter and that such a contribution becomes dominant at late times. By means of the WKB approximation, we find that these results can be extended to arbitrary RobertsonWalker geometries. We study the range of parameters in which the vacuum energy density would be compatible with current limits on dark matter abundance. Finally, by calculating the vacuum energy in a perturbed RobertsonWalker background, we obtain the speed of sound of density perturbations and show that the vacuum energy density contrast can grow on subHubble scales as in standard cold dark matter scenarios.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present a study of the Galactic Center region as a possible source of both secondary gammaray and neutrino fluxes from annihilating dark matter. We have studied the gammaray flux observed by the High Energy Stereoscopic System (HESS) from the J1745290 Galactic Center source. The data are well fitted as annihilating dark matter in combination with an astrophysical background. The analysis was performed by means of simulated gamma spectra produced by Monte Carlo event generators packages. We analyze the differences in the spectra obtained by the various Monte Carlo codes developed so far in particle physics. We show that, within some uncertainty, the HESS data can be fitted as a signal from a heavy dark matter density distribution peaked at the Galactic Center, with a powerlaw for the background with a spectral index which is compatible with the FermiLarge Area Telescope (LAT) data from the same region. If this kind of dark matter distribution generates the gammaray flux observed by HESS, we also expect to observe a neutrino flux. We show prospective results for the observation of secondary neutrinos with the Astronomy with a Neutrino Telescope and Abyss environmental RESearch project (ANTARES), Ice Cube Neutrino Observatory (Ice Cube) and the Cubic Kilometer Neutrino Telescope (KM3NeT). Prospects solely depend on the device resolution angle when its effective area and the minimum energy threshold are fixed.04/2014; 
Article: Vacuum energy as dark matter
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ABSTRACT: We consider the vacuum energy of massive quantum fields in an expanding universe. We define a conserved renormalized energymomentum tensor by means of a comoving cutoff regularization. Using exact solutions for de Sitter spacetime, we show that in a certain range of mass and renormalization scales there is a contribution to the vacuum energy density that scales as nonrelativistic matter and that such a contribution becomes dominant at late times. By means of the WKB approximation, we find that these results can be extended to arbitrary RobertsonWalker geometries. We study the range of parameters in which the vacuum energy density would be compatible with current limits on dark matter abundance. Finally, by calculating the vacuum energy in a perturbed RobertsonWalker background, we obtain the speed of sound of density perturbations and show that the vacuum energy density contrast can grow on subHubble scales as in standard cold dark matter scenarios.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The spectral study of the HESS J1745290 high energy gammaray cutoff from the galactic center is compatible with a signal of Dark Matter (DM) annihilation or decay. If this is the case, a neutrino flux from that source is also expected. We analyze the neutrino flux predicted by DM particles able to originate the HESS J1745290 gammarays observations. We focus on the electroweak and hadronic channels, which are favoured by present measurements. In particular, we study DM annihilating into W+W and uubar with DM masses of 48.8 and 27.9 TeV respectively. We estimate the resolution angle and exposition time necessary to test the DM hypothesis as the origin of the commented gamma signal.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: In this work we address the issue of studying the conditions required to guarantee the Focusing Theorem for both null and timelike geodesic congruences by using the Raychaudhuri equation. In particular we study the case of FriedmannRobertsonWalker as well as more general Bianchi Type I spacetimes. The fulfillment of the Focusing Theorem is mandatory in small scales since it accounts for the attractive character of gravity. However, the Focusing Theorem is not satisfied at cosmological scales due to the measured negative deceleration parameter. The study of the conditions needed for congruences convergence is not only relevant at the fundamental level but also to derive the viability conditions to be imposed on extended theories of gravity describing the different expansion regimes of the universe. We illustrate this idea for f(R) gravity theories.Journal of Cosmology and Astroparticle Physics 01/2014; 2014(03). · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We show that the energymomentum tensor of homogeneous fields of arbitrary spin in an expanding universe is always isotropic in average provided the fields remain bounded and evolve rapidly compared to the rate of expansion. An analytic expression for the average equation of state is obtained for Lagrangians with generic powerlaw kinetic and potential terms. As an example we consider the behavior of a spintwo field in the standard FierzPauli theory of massive gravity. The results can be extended to general spacetime geometries for locally inertial observers.Journal of Cosmology and Astroparticle Physics 11/2013; 2014(03). · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The gammaray fluxes observed by the High Energy Stereoscopic System (HESS) from the J1745290 Galactic Center source is well fitted by the secondary photons coming from Dark Matter (DM) annihilation in particleantiparticle standard model pairs over a diffuse powerlaw background. The spectral features of the signal are consistent with different channels: light quarks, electroweak gauge bosons and topantitop production. The amount of photons and morphology of the signal localized within a region of few parsecs, require compressed DM profiles as those resulting from baryonic contraction, which offer large enhancements in the signal over DM alone simulations. The fits return a heavy WIMP, with a mass above 10 TeV, but well below the unitarity limit for thermal relic annihilation. The fitted background spectral index is compatible with the FermiLarge Area Telescope (LAT) data from the same region. This possibility can be potentially tested with the observations of other high energy cosmic rays.10/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We study the possibility of testing some generic properties of brane world scenarios at the LHC. In particular, we pay attention to KaluzaKlein graviton and branon production. Both signals can be dominant depending on the value of the brane tension. We analyze the differences between these two signatures. Finally, we use recent data in the single photon channel from the ATLAS Collaboration to constrain the parameter space of both phenomenologies.Physical Review D 10/2013; 88(7). · 4.69 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Gauge bosons associated to new gauge symmetries under which the standard model particles are not charged are predicted in many extensions of the standard model of particles and interactions. We show that under very general conditions, the average energymomentum tensor of these rapidly oscillating vector fields is isotropic for any locally inertial observer. This result has a fundamental importance in order to consider coherent vector fields as a viable alternative to support models of dark matter, dark energy or inflation.09/2013;  [Show abstract] [Hide abstract]
ABSTRACT: Superweakly interacting massive particles produced in the late decays of weakly interacting massive particles (WIMPs) are generic in large regions of supersymmetric parameter space and other frameworks for physics beyond the standard model. If their masses are similar to that of the decaying WIMP, then they could naturally account for all of the cosmological dark matter abundance. Their astrophysical consequences and collider signatures are distinct and different from WIMP candidates. In particular, they could modify Big Bang Nucleosynthesis, distort the Cosmic Microwave Background, reduce galactic substructure and lower central densities of lowmass galaxies.08/2013;  [Show abstract] [Hide abstract]
ABSTRACT: In the context of scalartensor theories we study the evolution of the density contrast for JordanFierzBransDicke theories in a FriedmannLemaitreRobertsonWalker Universe. Calculations are performed in the Einstein Frame with the cosmological background described as LambdaCold Dark Matter (LambdaCDM) and supplemented by a JordanFierzBransDicke field. By using a completely general procedure valid for all scalartensor theories, we obtain the exact fourthorder differential equation for the density contrast evolution in modes of arbitrary size. In the case of subHubble modes, the expression reduces to a simpler but still fourthorder equation that is then compared with the standard (quasistatic) approximation. Differences with respect to the evolution as predicted by the standard Concordance LambdaCDM model are observed depending on the value of the coupling.Physical Review D 07/2013; · 4.69 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the differences in the gamma ray spectra simulated by four Monte Carlo event generator packages developed in particle physics. Two different versions of PYTHIA and two of HERWIG are analyzed, namely PYTHIA 6.418 and HERWIG 6.5.10 in Fortran and PYTHIA 8.165 and HERWIG 2.6.1 in C++. For all the studied channels, the intrinsic differences between them are shown to be significative and may play an important role in misunderstanding dark matter signals.05/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We study the main spectral features of the gammaray fluxes observed by the High Energy Stereoscopic System (HESS) from the J1745290 Galactic Center source during the years 2004, 2005 and 2006. In particular, we show that these data are well fitted as the secondary gammarays photons generated from dark matter annihilating into Standard Model particles in combination with a simple power law background. We present explicit analyses for annihilation in a single standard model particleantiparticle pair. In this case, the best fits are obtained for the u and d quarkantiquark channels and for the WW and ZZ gauge bosons, with background spectral index compatible with the FermiLarge Area Telescope (LAT) data from the same region. The fits return a heavy WIMP, with a mass above 10 TeV approximately, but well below the unitarity limit for thermal relic annihilation.Journal of Cosmology and Astroparticle Physics 02/2013; 2013(04). · 6.04 Impact Factor 
Article: CPT analysis with top physics
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ABSTRACT: We discuss the possibility of observing CPT violation from top antitop production in hadronic colliders. We study a general approach by analyzing constraints on the mass difference between the top and antitop quarks. We present current bounds from Tevatron data, and comment on the prospects for improving these bounds at the LHC and the ILC.Hyperfine Interactions 01/2013; 215(13). · 0.21 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In General Relativity without a cosmological constant a nonpositive contribution from the spacetime geometry to Raychaudhuri equation is found provided that particular energy conditions are assumed and regardless the considered solution of the Einstein's equations. This fact is usually interpreted as a manifestation of the attractive character of gravity. Nevertheless, a positive contribution to Raychaudhuri equation from spacetime geometry should occur since this is the case in an accelerated expanding RobertsonWalker model for congruences followed by fundamental observers. Modified gravity theories provide the possibility of a positive contribution although the standard energy conditions are assumed. We address this important issue in the context of f(R) theories, deriving explicit upper bounds for the contribution of spacetime geometry to the Raychaudhuri equation. Then, we examine the parameter constraints for some paradigmatic f(R) models in order to ensure a positive contribution to this equation. Furthermore, we consider the implications of these upper bounds in the equivalent formulation of f(R) theories as a BransDicke model.Journal of Cosmology and Astroparticle Physics 12/2012; 2013(07). · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We consider homogeneous nonabelian vector fields with general potential terms in an expanding universe. We find a mechanical analogy with a system of N interacting particles (with N the dimension of the gauge group) moving in three dimensions under the action of a central potential. In the case of bounded and rapid evolution compared to the rate of expansion, we show by making use of a generalization of the virial theorem that for arbitrary potential and polarization pattern, the average energymomentum tensor is always diagonal and isotropic despite the intrinsic anisotropic evolution of the vector field. We consider also the case in which a gaugefixing term is introduced in the action and show that the average equation of state does not depend on such a term. Finally, we extend the results to arbitrary background geometries and show that the average energymomentum tensor of a rapidly evolving YangMills fields is always isotropic and has the perfect fluid form for any locally inertial observer.Physical review D: Particles and fields 12/2012; 87(4).  [Show abstract] [Hide abstract]
ABSTRACT: The gravitational collapse in fourth order theories of gravity defined by an arbitrary action of the scalar curvature shows significant deviations with General Relativity. The presence of a new scalar mode produces a higher initial contraction that favors the reduction of the collapsing time. However, depending on the particular model, there are fundamental differences when the modifications to the General Relativity collapse leave the linear regime. These analyses can be used to exclude an important region of the parameter space associated with alternative gravitational models.10/2012;  [Show abstract] [Hide abstract]
ABSTRACT: We study the accelerated expansion of the Universe through its consequences on a congruence of geodesics. We make use of the Raychaudhuri equation which describes the evolution of the expansion rate for a congruence of timelike or null geodesics. In particular, we focus on the spacetime geometry contribution to this equation. By straightforward calculation from the metric of a RobertsonWalker cosmological model, it follows that in an accelerated expanding Universe the spacetime contribution to the Raychaudhuri equation is positive for the fundamental congruence, favoring a nonfocusing of the congruence of geodesics. However, the accelerated expansion of the present Universe does not imply a tendency of the fundamental congruence to diverge. It is shown that this is in fact the case for certain congruences of timelike geodesics without vorticity. Therefore, the focusing of geodesics remains feasible in an accelerated expanding Universe. Furthermore, a negative contribution to the Raychaudhuri equation from spacetime geometry which is usually interpreted as the manifestation of the attractive character of gravity is restored in an accelerated expanding RobertsonWalker spacetime at high speeds.Journal of Cosmology and Astroparticle Physics 08/2012; 2012(12). · 6.04 Impact Factor
Publication Stats
1k  Citations  
122.22  Total Impact Points  
Top Journals
Institutions

2001–2014

Complutense University of Madrid
 • Department of Theoretical physics I
 • Departamento de Estadística e Investigación Operativa III
Madrid, Madrid, Spain


2010

St. Cloud State University
Saint Cloud, Minnesota, United States


2008–2010

University of Minnesota Duluth
 Department of Physics
Duluth, Minnesota, United States


2005–2007

University of California, Irvine
 Department of Physics and Astronomy
Irvine, CA, United States
