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En este proyecto se ha pretendido introducir a estudiantes de grado a la computación cuántica práctica, mediante la incorporación de recursos educativos adecuados a los ordenadores cuánticos en desarrollo accesibles a través de servicios en la nube.

The purpose of this Thesis is to improve our understanding of the strong-field regime of gravitational interactions, where deviations from the theory of General Relativity (GR) are expected to be found on theoretical grounds. In particular, our investigations have been concerned with the formulation and application of junction conditions (which govern stellar collapse, black-hole formation and the dynamics of more exotic compact objects), as well as with other viability criteria necessary for modified gravity theories and their solutions to be physically admissible (such as stability or the avoidance of singularities). We will concentrate on two paradigmatic modifications of GR, namely, f (R) theories (specially on the metric formulation) and the ghost-free sub-class of Poincaré Gauge Gravity..., El propósito de esta Tesis es mejorar nuestro entendimiento del régimen de campo fuerte de las interacciones gravitacionales, donde, desde un punto de vista teórico, se espera encontrar desviaciones de la teoría de la Relatividad General (RG). En particular, nuestras investigaciones se han centrado en la formulación y aplicación de las condiciones de pegado (que gobiernan el colapso gravitacional, la formación de agujeros negros y la dinámica de objetos compactos más exóticos), así como en otros criterios de viabilidad necesarios para que las teorías de gravedad modificada y sus soluciones sean físicamente admisibles (como la estabilidad o la evasión de singularidades). Nos concentraremos en dos modificaciones paradigmáticas de la RG, a saber, las teorías f (R) (especialmente en su formulación métrica) y en la subclase libre de ghosts de la Gravedad Gauge Poincaré...

© 2023 American Physical Society The authors thank J. A. Oller for reading the manuscript and useful comments. This research is partly supported by the Ministerio de Ciencia e Innovacion under research Grants No. PID2019-108655 GB-I00, No. PID2019- 105614 GB-C21, and No. PID2021-124473NB-I00 (R. L. Delgado) and the "Unit of Excellence Maria de Maeztu 2020-2023" award to the Institute of Cosmos Sciences (CEX2019-000918-M), and the Grant No. 2017-SGR-929 from Generalitat de Catalunya. R. L. Delgado was also financially supported by the Ramon Areces Foundation postdoctoral fellowship, the Istituto Nazionale di Fisica Nucleare (INFN) postdoctoral Fellowship No. AAOO DGF-2019-0000329., Some effective field theories exhibit dynamical resonances that, when properly included, mitigate their bad behavior at high energies. Unitarization of the partial wave amplitudes is the preferred method to unveil such resonances. Interpreting the Einstein-Hilbert theory in the spirit of effective Lagrangians, we implement the inverse amplitude method and unitarize the one-loop level graviton-graviton scattering in pure gravity. Due to the presence of infrared divergences, the analysis requires a careful treatment of the infrared region and the introduction of infrared regulators, carefully selected in order to fulfill perturbative unitarity., Ministerio de Ciencia e Innovación (MICINN), Generalitat de Catalunya, Unidad de Excelencia María de Maeztu (MICINN), Istituto Nazionale di Fisica Nucleare (INFN), Fundación Ramón Areces, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©1992 The American Physical Society. One of the authors (A.D.) would like to thank S. Dimopoulos and M. J. Herrero for continuous encouragement and T. N. Truong for useful discussions on the unitarity problem. A.D. thanks also the CERN TH-Division for hospitality at the early and Anal parts of this work. This work has been supported in part by the Ministerio de Educacion y Ciencia (Spain) (CICYT Project No. AEN90-0034)., If the symmetry-breaking sector of the standard model is strongly interacting, the low-energy dynamics of the longitudinal components of the weak bosons can be described by a nonlinear-sigma-model with two free parameters. For a large range of these parameters the model supports finite-energy solitons called weak Skyrmions or technibaryons. Technibaryons could be produced at the Superconducting Super Collider giving rise to exotic experimental signatures since they are stable, heavy, and in some cases, fractional-charged particles., Ministerio de Educacion y Ciencia (Spain), CICYT, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©2003 The American Physical Society, We consider a general brane-world model parametrized by the brane tension scale f and the branon mass M. For a low tension compared to the fundamental gravitational scale, we calculate the relic branon abundance and its contribution to the cosmological dark matter. We compare this result with the current observational limits on the total and hot dark matter energy densities and derive the corresponding bounds on f and M. Using the nucleosynthesis bounds on the number of relativistic species, we also set a limit on the number of light branons in terms of the brane tension. Finally, we estimate the bounds coming from the energy loss rate in supernovae explosions due to massive branon emission., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 1996 Elsevier Science B.V.. This work has been supported in part by the Ministerio de Education y Ciencia (Spain) (CICYT AEN93- 0776) and COLCIENCIAS (Colombia). The authors thank F. Cornet, J.F. Donoghue, J. Gasser and J.R. Pelaez for useful information and discussions., In this work we present the results of a complete calculation of the gamma gamma --> pi(0) pi(0) amplitude to leading order in the large N approximation (N being the number of Goldstone bosons) up to order m(pi)(2)/F-2, The amplitude turns to be proportional a to that of pi(+)pi(-) --> pi(0) pi(0). In spite of the fact that this factorization property cannot hold in general (as it was recently pointed our by Morgan and Penington), it appears here since in the large N limit only the I = J = 0 channel contributes to the gamma gamma --> pi(0) pi(0) reaction. Moreover it seems to be a reasonable approximation in this case since it is possible to reproduce, as a prediction, the experimental data starting from a one-parameter fit of the pi pi scattering data., Ministerio de Education y Ciencia (Spain), CICYT, COLCIENCIAS (Colombia), Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 The American Physical Society, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© SISSA 2005 We thank D.T. Son, R. Pisarski and L. Yaffe for very useful discussions. C.M. thanks the I.N.T. at the University of Washington for its hospitality and partial support during the completion of this article. This work has been supported by grants FPA 2000-0956, BFM 2002-01003, FPA2001-3031 from MCYT (Spain), We compute the mean free path and shear viscosity in the color-flavor locked (CFL) phase of dense quark matter at low temperature T, when the contributions of mesons, quarks and gluons to the transport coefficients are Boltzmann suppressed. CFL quark matter displays superfluid properties, and transport phenomena in such cold regime are dominated by phonon-phonon scattering. We study superfluid phonons within thermal field theory and compute the mean free path associated to their most relevant collision processes. Small-angle processes turn out to be more efficient in slowing transport phenomena in the CFL matter, while the mean free path relevant for the shear viscosity is less sensitive to collinear scattering due to the presence of zero modes in the Boltzmann equation. In analogy with superfluid He-4, we find the same T power law for the superfluid phonon damping rate and mean free path. Our results are relevant for the study of rotational properties of compact stars, and correct wrong estimates existing in the literature., MCYT (Spain), Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 American Institute of Physics. We thank the organizers of the XIII Mexican School of Particles and Fields for this very successful meeting. Mexican Workshop on Particles and Fields (13. 2008. Hermosillo, Méjico). We thank the organizers of the XIII Mexican School of Particles and Fields for this very successful meeting. Work supported by grants BSCH-PR34/07-15875, FPA 2004 02602,FPA 2005-02327, and Accion Integrada Hispano-Portuguesa HP2006-0018., The viscosity over entropy density ratio, or KSS number, can help isolate the critical point in the hadron phase-diagram in Relativistic Heavy Ion Collisions. We argue that this quantity does have a minimum at a phase transition or crossover. Although indications from conventional non-relativistic gases point out to even a divergence in eta/s when the phase-transition is first-order, since the critical exponent is rather low, this will be more difficult to ascertain in RHIC or FAIR. The experimental data are more likely to reveal a discontinuity for a first order phase transition or a smooth minimum at a crossover., Accion Integrada Hispano-Portuguesa, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 IOP Publishing Ltd and SISSA. This work has been partially supported by the DGICYT (Spain) under projects FPA200402602, FPA2005-02327 and CAM/UCM 910309, by UCM-Santander PR34/07-15875 and by DOE grant DOE/DE-FG02-94ER40823., One of the most striking features found in the cosmic microwave background data is the presence of an anomalous cold spot (CS) in the temperature maps made by the Wilkinson Microwave Anisotropy Probe (WMAP). This CS has been interpreted as the result of the presence of a collapsing texture, perhaps coming from some early universe grand unified theory (GUT) phase transition. In this work we propose an alternative explanation based on a completely different kind of texture which appears in a natural way in a broad class of brane-world models. This type of texture, known as a brane-skyrmion, can be understood as a hole in the brane which makes it possible to pass through them along the extra-dimensional space. The typical scales needed for the proposed brane-skyrmions to correctly describe the observed CS can be as low as the electroweak scale., DGICYT (Spain), UCM-Santander, DOE, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2010 IOP Publishing Ltd. Spanish Relativity Meeting (2009). This work has been supported by the MICINN (Spain) project numbers FIS 2008-01323 and FPA 2008-00592, UCM-Santander PR34/07-15875 and UCM-BSCH GR58/08 910309, In the context of f(R) gravity theories, the issue of finding static and spherically symmetric black hole solutions is addressed. Two approaches to study the existence of such solutions are considered: first, constant curvature solutions, and second, the general case (without imposing constant curvature) is also studied. Performing a perturbative expansion around the Einstein-Hilbert action, it is found that only solutions of the Schwarzschild-(Anti-) de Sitter type are present (up to second order in perturbations) and the explicit expressions for these solutions are provided in terms of the f(R) function. Finally we consider the thermodynamics of black holes in Anti-de Sitter space-time and study their local and global stability., MICINN (Spain), UCM-Santander, UCM-BSCH, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society. This work is partially supported by DGICYT (Spain) under project numbers FPA 2004-02602 and BFM 2002- 01003, by NSF grant No. PHY-0239817 and by the Fulbright-MEC (Spain) program., We study the possibility to explain the nonbaryonic dark matter abundance and improve the present fits on the muon anomalous magnetic moment through the same new physics. In this work we show that massive brane fluctuations (branons) in large extra-dimensions models can provide an economical way to deal with these two issues. This is so because the low-energy branon physics depends effectively on essentially only three parameters. Next collider experiments, such as LHC or ILC, will be sensitive to branon phenomenology in the natural parameter region where the theory is able to account for the two effects., DGICYT (Spain), NSF grant, Fulbright-MEC (Spain), Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 1996 The American Physical Society. The authors thank L. Alvarez-Gaumé for useful discussions. We would also like to thank A. Gómez Nicola for his suggestions. This work was partially supported by the Ministerio de Educación y Ciencia (Spain) (CICYT AEN95-1285-E)., Using the Fujikawa and the heat-kernel methods we make a complete and detailed computation of the global, gauge, and gravitational anomalies in the standard model defined on a curved space-time with torsion. We find new contributions coming from the curvature and the torsion to the leptonic number anomaly (so that B-L is not conserved anymore) to the U(1)(Y) gauge and to the mixed U(1)(Y)-gravitational anomalies. However, neither gauge nor gravitational new anomaly cancellation conditions for the hypercharges arise., Ministerio de Educación y Ciencia (Spain), CICYT, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© Springer. Conference on Network for Ultra Violet Astronomy (2007. Madrid, España). This work has been partially supported by the DGICYT (Spain) under the project numbers FPA 2004-02602 and FPA 2005-02327 and by the Universidad Complutense/CAM: project number 910309. A.D. thanks Ana I. Gómez de Castro for her kind invitation to participate in the NUVA Conference, In this work we review briefly the origin and history of the cosmological constant and its recent reincarnation in the form of the dark energy component of the universe. We also comment on the fundamental problems associated to its existence and magnitude which require an urgent solution for the sake of the internal consistency of theoretical physics., DGICYT (Spain), Universidad Complutense/CAM, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society. We would like to thank J. A. R. Cembranos and very specially A. L. Maroto for useful comments and discussions. We also thank S. D. Odintsov for bringing to our attention [13], where special functions are also considered as f(R)candidates for cosmologically viable models. This work has been partially supported by the DGICYT (Spain) under the project No. FPA2005-02327., In this work we consider the possibility of describing the current evolution of the universe, without the introduction of any cosmological constant or dark energy (DE), by modifying the Einstein-Hilbert (EH) action. In the context of the f(R) gravities within the metric formalism, we show that it is possible to find an action without cosmological constant which exactly reproduces the behavior of the EH action with cosmological constant. In addition the f(R) action is analytical at the origin having Minkowski and Schwarzschild solutions as vacuum solutions. The found f(R) action is highly nontrivial and must be written in terms of hypergeometric functions but, in spite of looking somewhat artificial, it shows that the cosmological constant, or more generally the DE, is not a logical necessity., DGICYT (Spain), Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

Open Access, © The Authors. AD thanks useful conversations with D. Espriu, M. J. Herrero and J. J. Sanz-Cillero. The work has been supported by the spanish grant FPA2011-27853-C02-01 and by the grant BES-2012-056054 (RLD)., By including the recently discovered Higgs-like scalar phi in the Electroweak Chiral Lagrangian, and using the Equivalence Theorem, we carry out the complete one-loop computation of the elastic scattering amplitude for the longitudinal components of the gauge bosons V = W, Z at high energy. We also compute phi phi -> phi phi and the inelastic process V V -> phi phi, and identify the counterterms needed to cancel the divergences, namely the well known a(4) and a(5) chiral parameters plus three additional ones only superficially treated in the literature because of their dimension 8. Finally we compute all the partial waves and discuss the limitations of the one-loop computation due to only approximate unitarity., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2003 The American Physical Society. This work has been partially supported by the DGICYT (Spain) under Projects No. FPA 2000-0956 and No. BFM2000-1326., We show that, in the context of brane-world scenarios with low tension [tau]=f^4, massive brane fluctuations (branons) are natural dark matter candidates. We calculate the present abundances for both hot (warm) and cold branons in terms of the branon mass M and the tension scale f. The results are compared with the current experimental bounds on these parameters. We also study the prospects for their detection in direct search experiments and comment on their characteristic signals in the indirect ones., DGICYT (Spain), Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 Elsevier Science B.V. All rights reserved. This work has been partially supported by the Ministerio de Educación y Ciencia (Spain) (CICYT AEN 97-1693 and PB98-0782)., We study, within the recently proposed brane-world scenario, the effective action for the low-energy brane excitations. These modes are understood as Goldstone bosons associated to the spontaneous isometry breaking, induced on the bulk space by the presence of the brane. Starting from the Nambu-Goto action for the brane, we obtain a non-lineal sigma model describing the low-energy interactions of the Goldstone bosons and extend the calculation up to O(p(4)). We also discuss the Higgs-like mechanism in which the Kaluza-Klein gauge fields absorb the Goldstone bosons and acquire mass. Finally, we present the explicit Form of the effective action describing the low-energy interactions between the three-brane Goldstone bosons and the particles present in the Standard Model., Ministerio de Educación y Ciencia (Spain), CICYT, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

We analyze the finite temperature (T) extension of the Wess-Zumino-Witten functional, discussed in a previous work, to one loop in chiral perturbation theory. As a phenomenological application, we calculate finite temperature corrections to the amplitude of pi0 decay into two photons. This calculation is performed in three limits : i) T/M(pi) << 1, ii) the chiral limit at finite T and iii) T/M(pi) >> 1 (M(pi) being the pion mass). The T-corrections tend to vanish in the chiral limit, where only the kaon contribution remains (although it is exponentially suppressed)., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

We develop an alternative formulation of the symmetry breaking sector of the Standard Model as a gauged non-linear sigma model (NLSM) following the philosophy of the Chiral lagrangian approach, which is the only compatible with all the experimental and theoretical constraints. We derive the BRS symmetry of the model and the corresponding quantum lagrangian, which is a generalization of the standard Faddeev-Popov method, in a way which is covariant with respect to the reparametrizations of the coset space of the NLSM. Then we use the BRS invariance of the quantum lagrangian to state the Equivalence Theorem for the renormalized S-matrix elements calculated as a chiral expansion., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© American Physical Society. We would like to thank A. Starobinsky for useful comments and J. A. R. Cembranos and J. Beltrán n for their continuous encouragement. This work has been partially supported by the DGICYT (Spain) under projects FPA 2004-02602, FPA 2005-02327, and CAM/UCM 910309 and by UCM-Santander PR34/07-15875., In the context of f(R) theories of gravity, we study the evolution of scalar cosmological perturbations in the metric formalism. Using a completely general procedure, we find the exact fourth-order differential equation for the matter density perturbations in the longitudinal gauge. In the case of sub-Hubble modes, the expression reduces to a second-order equation which is compared with the standard (quasistatic) equation used in the literature. We show that for general f(R) functions the quasistatic approximation is not justified. However, for those functions adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it provides a correct description for the evolution of perturbations., DGICYT (Spain), CAM/UCM, UCM-Santander, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2013 American Physical Society. The authors thankfully acknowledge the computer resources, technical expertise, and assistance provided by the Barcelona Supercomputing Centre—Centro Nacional de Supercomputación—and the Tirant supercomputer support staff at Valencia. We are also pleased to thank Professor Antonio L. Maroto and Professor Torbjo¨rn Sjöstrand for their useful help and comments. This work has been supported by MICINN (Spain) Project Nos. FIS 2008-01323, FIS2011-23000, and FPA2011-27853-01 and Consolider-Ingenio MULTIDARK CSD2009-00064. R. L.D. is a fellow of FPI, Ref. BES-2012-056054., We explore the viscosities of a photon gas by means of the Euler-Heisenberg effective theory and quantum electrodynamics at zero electron chemical potential. We find parametric estimates that show a very large shear viscosity and an extremely small bulk viscosity (reflecting the very weak coupling simultaneously with a very approximate dilatation invariance). The system is of some interest because it exemplifies very neatly the influence of the breaking of scale invariance on the bulk viscosity., MICINN (Spain), Consolider-Ingenio MULTIDARK, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2014 IOP Publishing Ltd Printed in the UK. FJLE thanks the hospitality of the NEXT institute and the high energy group at the University of Southampton, ADG thanks the CERN-TH, and both the hospitality of the ECT* at Trento during the final stages of this work. This work was supported by Spanish grant FPA2011- 27853-C02-01 and by the grant BES-2012-056054 that supports RDL., The claimed finding of a light Higgs boson makes the minimal Standard Model unitary. Yet, we recall that the general low-energy dynamics for the minimal electroweak symmetry breaking sector with three Goldstone bosons and one light scalar is not so. We construct the effective Lagrangian for these four particles and their scattering amplitudes, that can be extracted from LHC experiments when longitudinal W, Z modes be properly isolated for E >> M-W (equivalence theorem). We then observe the known increase in interaction strength with energy and explore various unitarization methods in the literature in the absence of other new physics (as LHC experiments fail to report anything up to 600 GeV). Our generic conclusion is that for most of parameter space the high-energy scattering of the longitudinal W's is strongly interacting (with the Minimal Standard Model a remarkable exception). We find and study a second sigma-like scalar pole of the WLWL amplitude, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

This paper attempts at contributing to the ongoing debate on the historical roots of the high economic inequality of contemporary Iberian America. Basically empirical, our approach departs from mainstream scholarship. We show new data on wages and heights in several viceroyalties that: 1) suggest relatively medium to high levels of material welfare among the commoners in Bourbon Hispanic America; 2) allow us to build indexes of economic inequality. An international comparison of those indexes casts some doubts on the widely accepted view that Viceroyal America’s economy was exclusively based on extremely unequal or extractive institutions, as it has been popularized by the influential works by Engerman and Sokoloff (1994, 2002, 2005), Acemoglu et al. (2002).[RESUMEN] Este trabajo pretende contribuir al debate sobre las causas históricas de la alta desigualdad económica en la Iberoamérica contemporénea y lo hace en forma básicamente empírica, lo que es bastante inusual. En él se muestran nuevos datos sobre salarios y estaturas de varios virreinatos que: (1) sugieren niveles de bienestar material relativamente medios o altos para grupos no privilegiados de la Hispanoamérica borbónica; y (2) permiten la construcción de índices de desigualdad económica. La comparación internacional de esos índices arroja dudas sobre la verosimilitud del ampliamente extendido supuesto de que la economía de la América española se basada exclusivamente en instituciones extremadamente desiguales o extractivas, que ha sido popularizada por los influyentes trabajos de Engerman y Sokoloff y Acemoglu et al., Depto. de Economía Aplicada, Estructura e Historia, Fac. de Ciencias Económicas y Empresariales, TRUE, pub

© 2009 The American Physical Society. We thank useful conversations and exchanges on eta/s with Jochen Wambach, Juan Maldacena, Dam Son, and Tom Cohen. This work has been supported by Grant Nos. FPA 2004-02602, 2005-02327, BSCH-PR34/0715875 (Spain), We present a calculation of eta/s for the meson gas (zero baryon number), with the viscosity computed within unitarized next-to-leading-order chiral perturbation theory, and confirm the observation that eta/s decreases towards the possible phase transition to a quark-gluon plasma/liquid. The value is somewhat higher than previously estimated in leading-order chi PT. We also examine the case of atomic Argon gas to check the discontinuity of eta/s across a first-order phase transition. Our results suggest employing this dimensionless number, sometimes called KSS number (in analogy with other ratios in fluid mechanics such as Reynolds number or Prandtl number) to pin down the phase transition and critical end point to a crossover in strongly interacting nuclear matter between the hadron gas and quark and gluon plasma/liquid., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2007 IOP Publishing Ltd. IRGAC Meeting (2006. Barcelona, España). This work has been partially supported by DGICYT (Spain) under project numbers FPA 2004- 02602 and FPA 2005-02327, by NSF grant no. PHY-0239817 and Fulbright-MEC Award., In this work, we will review the main properties of braneworld models with low tension. Starting from very general principles, it is possible to obtain an effective action for the relevant degrees of freedom at low energies (branons). Using the cross sections for high-energy processes involving branons, we set bounds on the different parameters appearing in these models. We also show that branons provide a WIMP candidate for dark matter in a natural way. We consider cosmological constraints on its thermal and non-thermal relic abundances. We derive direct detection limits and compare those limits with the preferred parameter region in the case in which the EGRET excess in the diffuse galactic gamma rays is due to dark matter annihilation. Finally, we will discuss the constraints coming from the precision tests of the standard model and the muon anomalous magnetic moment., DGICYT (Spain), NSF, Fulbright-MEC Award, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© World Scientic Publishing Company. We are grateful to B. Nodland for his comments to the preliminary version of this letter and also to J. P. Ralston for his suggestions. This work has been supported in part by the Ministerio de Educaci_on y Ciencia (Spain) (CICYT AEN96-1634)., In this letter we provide a simple explanation of the recent finding of anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston. We consider, as a possible origin of such effect, the effective coupling between EM fields and some tiny background torsion field. The coupling is obtained after integrating out charged fermions, it is gauge-invariant and does not require the introduction of any new physics., Ministerio de Educación y Ciencia (Spain), CICYT, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 1993The American Physical Society. This work has been partially supported by the Ministerio de Educacion y Ciencia (Spain) (CICYT AEN 90-0034), We apply the one-loop results of the SU(3)L X SU(3)R chiral perturbation theory supplemented with the inverse-amplitude method to fit the available experimental data on pipi and piK scattering. With essentially only three parameters we describe accurately data corresponding to six different channels: namely, (I,J) = (0,0), (2,0), (1,1), (1/2, 0), (3/2, 0), and (1/2, 1). In addition we reproduce the first resonances of the (1, 1) and (1/2, 1) channel with the right mass corresponding to the rho and the K* (892) particles., Ministerio de Educación y Ciencia (Spain), CICYT, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

We would like to thank the TH division at CERN for financial support and for their kind hospitality. We appreciate the continous encouragement from D. Denegri and thank him for the various discussions and useful comments on this and related subjects. We thank T. Rodrigo and the CMS Collaboration for discussions. This work has been partially supported by the Spanish Ministerio de Education y Ciencia under projects CICYT AEN93-0673, AEN90-0034 and AEN93-0776., In the present work we study the predictions for WZ and ZZ production at the LHC with the Electroweak Chiral Lagrangian (EChL) approach. Our analysis will be focused on the less favored case from the experimental point of view, in which the predictions for the gauge bosons scattering amplitudes are considered in the low energy range where, by construction of the low energy approach, they reveal no resonant behavior. The study includes the complete set of amplitudes for all the polarization states of the initial and/or final gauge bosons and makes no use of the Equivalence Theorem. We express the results in terms of the range of values of the chiral parameters that will be accessible at the LHC., Spanish Ministerio de Education y Ciencia, CICYT, CERN TH division, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 1997 The American Physical Society. J.R.P would like to thank the Theory Group at Berkeley for their kind hospitality, the Jaime del Amo fundation for financial support, as well as M.J. Herrero and H.J. He for helpful discussions on the subject. This work has been partially supported by the Ministerio de Educación y Ciencia (Spain) Grant No. CICYT AEN93-0776)., In this work we study the applicability of the equivalence theorem, either for unitary models or within an effective Lagrangian approach. There are two types of limitations: the existence of a validity energy window and the use of the lowest order in the electroweak constants. For the first kind, we consider some methods, based on dispersion theory or the large N limit, that allow us to extend the applicability. For the second, we obtain numerical estimates of the effect of neglecting higher orders in the perturbative expansion. [S0556-2821(97)04421-4]., Ministerio de Educación y Ciencia (Spain), CICYT, Jaime del Amo fundation, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

This work is supported by the DGICYT (Spain) project BPA2005-02327, by the Universidad Complutense/CAM projects 910309 and CCG06-UCM/ESP-137, and by the MEC (Spain) projects CTQ2005-09185-C02-02 and FIS2004-03267. The work of PB was supported by the FPI grant BES-2006-11976 from the Spanish MEC. The authors would like to thank A. L. Maroto and R. Pérez de Tudela for useful discussions., We examine the effect of cold dark matter on the discrimination between the two enantiomers of a chiral molecule. We estimate the energy difference between the two enantiomers due to the interaction between fermionic WIMPs (weak interacting massive particles) and molecular electrons on the basis that electrons have opposite helicities in opposite enantiomers. It is found that this energy difference is completely negligible. Dark matter could then be discarded as an inductor of chiroselection between enantiomers and then of biological homochirality. However, the effect of cosmological neutrinos, revisited with the currently accepted neutrino density, would reach, in the most favorable case, an upper bound of the same order of magnitude as the energy difference obtained from the well-known electroweak electron-nucleus interaction in some molecules., DGICYT (Spain), Universidad Complutense/CAM, MEC (Spain), Depto. de Óptica, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© Springer-Verlag 1999, The possibility of a heavy supersymmetric spectrum at the Minimal Supersymmetric Standard Model is considered and the decoupling from the low energy electroweak scale is analyzed in detail. The formal proof of decoupling of supersymmetric particles from low energy physics is stated in terms of the effective action for the particles of the Standard Model that results by integrating out all the sparticles in the limit where their masses are larger than the electroweak scale. The computation of the effective action for the standard electroweak gauge bosons W+/-, Z and gamma is performed by integrating out all the squarks, sleptons, charginos and neutralinos to one-loop. The Higgs sector is not considered in this paper. The large sparticle masses limit is also analyzed in detail. Explicit analytical formulae for the two-point functions of the electroweak gauge bosons to be Valid in that limit are presented. Finally, the decoupling of sparticles in the S, T and U parameters is studied analitically. A discussion on how the decoupling takes place in terms of both the physical sparticle masses and the not-physical mass parameters as the mu-parameter and the soft-breaking parameters is included., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2011 American Physical Society. This work has been supported in part by MICINN (Spain) Projects No. FIS 2008-01323 and No. FPA 2008-00592, CAM/UCM 910309, MEC Grant No. BES-2006-12059, DOE Grant No. DE-FG02-94ER40823 and MICINN Consolider-Ingenio MULTIDARK CSD2009-00064. We are particularly grateful to Professor Jonathan Feng for his continuous and encouraging help at UC Irvine during the summer of 2007. We would also like to thank Dr. Mario Bondioli for his preliminary help with simulation software and Dr. Mirco Cannoni, Professor Mario E. Gómez and Professor Mikhail Voloshin for interesting discussions about different aspects of the physical meaning of the spectra behavior. Dr. Abelardo Moralejo drew our attention of some particular aspects of bremsstrahlung. Finally, fruitful discussions were held with Daniel Nieto about detectors' technicalities and improvement of the numerical codes. R. L. acknowledges financial support given by Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR), by the University of Torino (UniTO), by the Istituto Nazionale di Fisica Nucleare (INFN) within the Astroparticle Physics Project, and by the Italian Space Agency (ASI) under Contract No. I/088/06/0. AdlCD wants to thank David Fernández (UCM) for his technical support with the performed simulations and Dr. Javier Almeida for his help to manage simulation results. Scientific discussions about other available simulation software were held with Beatriz Canadas., If the present dark matter in the Universe annihilates into standard model particles, it must contribute to the fluxes of cosmic rays that are detected on the Earth and, in particular, to the observed gamma-ray fluxes. The magnitude of such a contribution depends on the particular dark matter candidate, but certain features of the produced photon spectra may be analyzed in a rather model-independent fashion. In this work we provide the complete photon spectra coming from WIMP annihilation into standard model particle-antiparticle pairs obtained by extensive Monte Carlo simulations. We present results for each individual annihilation channel and provide analytical fitting formulas for the different spectra for a wide range of WIMP masses., Ministerio de Ciencia e Innovación, Ministerio de Educación y Ciencia, Ministero dell'Istruzione, dell'Università e della Ricerca, University of Torino, Istituto Nazionale di Fisica Nucleare within the Astroparticle Physics Project, Italian Space Agency, MICINN Consolider-Ingenio MULTIDARK, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©The American Physical Society. The authors want to thank A. Gomez Nicola and J. R. Pelaez for reading the manuscript. This work has been partially supported by the Ministerio de Educación y Ciencia (Spain) (CICYT AEN 97-1693 and PB98-0782)., By using chiral perturbation theory and the Uehling-Uhlenbeck equation we compute the viscosity of a pion gas, in the low temperature and low density regime, in terms of the temperature and the pion fugacity. The viscosity turns out to be proportional to the square root of the temperature over the pion mass. Next to leading corrections are proportional to the temperature over the pion mass to 3/2., CICYT, Ministerio de Educación y Ciencia (Spain), Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©2002 The American Physical Society. This work has been supported in part by the Spanish Ministerio de Ciencia y Tecnología under projects CICYT FPA 2000-0980, CICYT AEN 97-1693 and PB98-0782., In this paper we study the Yukawa Higgs-quark-quark interactions that are generated from radiative corrections of squarks and gluinos, in the minimal supersymmetric standard model. We compute the corrections to the effective action for Higgs and quark fields that are produced by explicit integration in the path integral formalism of all the squarks and gluinos at the one-loop level and order alpha(s). In addition, we consider the limit of nearly degenerate heavy squarks and gluinos, with masses much larger than the electroweak scale, and we derive the effective Lagrangian containing all the relevant new local Higgs-quark-quark interactions. We show that these new interactions do remain nonvanishing, even in the case of infinitely heavy supersymmetric particles and, therefore, we demonstrate explicitly the nondecoupling behavior of squarks and gluinos in Higgs bosons physics. We present the set of new Yukawa couplings and finally derive the corresponding one-loop, order alpha(s), corrections to the Higgs bosons partial decay widths into quarks., Spanish Ministerio de Ciencia y Tecnología, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© Springer-Verlag / Società Italiana di Fisica 2007. We thank T. Cohen and D.T. Son for enthusiastic correspondence about possible improvements to the original preprint. This work has been supported by grants FPA 2004-02602, 2005-02327, PR27/05-13955-BSCH (Spain)., A computation of the quotient of shear viscosity and entropy density, or the Kovtun, Son and Starinets (KSS) number eta/s, is performed in the non-relativistic and classical regime, first in chiral perturbation theory, and then in the SO(g + 1)ISO(g) non-linear sigma model in the large g limit. Both are field theories stemming from a renormalizable sigma model, but, in spite of that, we explicitly calculate how one avoids the KSS bound by increasing the number of degenerate pions sufficiently. However, we argue that particle production could still keep the validity of the KSS bound in the weak sense. We also show how a large number of molecular isomers (which we estimate in terms of simple molecular properties) could avoid the bound in the strong sense. This might be possible with carbon based molecules. We finally argue that a measurement of eta/s in heavy-ion collisions might be turned into an upper bound on the number of hadron resonances., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©2002 The American Physical Society. Work supported by the Spanish CICYT projects, Grant Nos. FPA2000-0956, PB98-0782, and BFM2000-1326. J.R.P. acknowledges support from the CICYT-INFN collaboration, Grant No. 003P 640.15, and E. Oset for useful comments., We study the temperature evolution of the rho and sigma mass and width, using a unitary chiral approach. The one-loop pipi scattering amplitude in chiral perturbation theory at Tnot equal0 is unitarized via the inverse amplitude method. Our results predict a clear increase with T of both the rho and sigma widths. The masses decrease slightly for high T, while the rhopipi coupling increases. The rho behavior seems to be favored by experimental results. In the sigma case, it signals chiral symmetry restoration., Spanish CICYT, CICYT-INFN, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub