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©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

© 2009 The American Physical Soci. We are grateful to D. Kharzeev, G. D. Moore, and C. Pica for very useful comments. This research was partially funded by research contracts No. FPA2004-02602, No. FPA2005-02327, No. FPA2007-29115-E, No. PR34- 1856-BSCH, No. UCM-CAM 10309, and No. FPI-BES- 2005-6726., We calculate the bulk viscosity of the massive pion gas within unitarized chiral perturbation theory. We obtain a low-temperature peak arising from explicit conformal breaking due to the pion mass and another peak near the critical temperature, dominated by the conformal anomaly through gluon condensate terms. The correlation between bulk viscosity and conformal breaking supports a recent QCD proposal. We discuss the role of resonances, heavier states, and large-N(c) counting., UCM-CAM, Depto. de Física Teórica, Fac. de Ciencias Físicas, 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

© 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

© Physical Society. This work has been partially supported by the Ministerio de Educacion y Ciencia (Spain) (CICYT AEN93-0776)., Whichever turns out to be the real theory of gravitation, the corresponding low-energy effective Lagrangian will probably contain higher derivative terms. In this work we study the general conditions on those terms in order to produce enough inflation to solve some of the problems of the standard Friedmann-Robert;son-Walker cosmology in the absence of any inflaton field. We apply our results to some particular scenarios where higher derivative terms appear in the effective Lagrangian for gravity, such as those coming from graviton (two) loops or integrating out ordinary matter (such as the one present in the standard model)., Ministerio de Educacion y Ciencia (Spain), CICYT, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 The American Physical Society. The authors thank A. Gómez Nicola, D. Fernández Fraile, F. Sols, and D. Antonov for useful discussions as well as T. Schaefer and N. Demir for providing us their=s data. This work was supported by Grants No. FPA2007-29115-E, No. PR34-1856-BSCH, No. FPA2008-00592, No. FIS2008-01323, No. UCM-BSCH GR58/08 910309, UCM-Santander No. PR34/07-15875, and an FPU grant to J. M. T.-R., We reexamine the possibility of employing the viscosity over entropy density ratio as a diagnostic tool to identify a Phase transition in hadron physics to the strongly coupled quark-gluon plasma and other circumstances where direct measurement of the order parameter or the free energy may be difficult. It has been conjectured that the minimum of eta/s does indeed occur at the phase transition. We now make a careful assessment in a controlled theoretical framework, the linear sigma model at large N, and indeed find that the minimum of eta/s occurs near the second-order phase transition of the model due to the rapid variation of the order parameter (here the sigma vacuum expectation value) at a temperature slightly smaller than the critical one., UCM-Santander, UCM-BSCH, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

©2004 The American Physical Society. The authors thank J. R. Peláez and A. Gómez Nicola for providing us with their SU(3) phase shifts and useful discussions, S. Santalla and F. J. Fernández for extensive checks and assistance, and D. Davesne for some interesting comments. This work was supported by grants FPA 2000-0956 and BFM 2002-01003 (Spain)., We report a calculation of the shear viscosity in a relativistic multicomponent meson gas as a function of temperature and chemical potentials. We approximately solve the Uehling-Uhlenbeck transport equation of kinetic theory, appropriate for a boson gas, with relativistic kinematics. Since at low temperatures the gas can be taken as mostly composed of pions, with a fraction of kaons and etas, we explore the region where binary elastic collisions with at least one pion are the dominant scattering processes. Our input meson scattering phase shifts are fits to the experimental data obtained from chiral perturbation theory and the inverse amplitude method. Our results take the correct nonrelativistic limit (viscosity proportional to the square root of the temperature), show a viscosity of the order of the cube of the pion mass up to temperatures somewhat below that mass, and then a large increase due to kaons and etas. Our approximation may break down at even higher temperatures, where the viscosity follows a temperature power law with an exponent near 3., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2007 The American Physical Society. This work is supported by DGICYT (Spain) under Project No. BPA2005-02327. The work of S. P. is supported by the I3P-Contract of CSIC at IFIC—Instituto de Física Corpuscular, Valencia. The work of L. TabaresCheluci is supported by a FPU grant from the Spanish M.E.C., In this work we compute the contributions to the Higgs effective potential coming from the fermion and gauge boson sectors at the one-loop level in the context of the SU(5)/SO(5) littlest Higgs (LH) model using a cutoff Lambda and including all finite parts. We consider both, the (SU(2) x U(1))(1) x (SU(2) x U(1))(2) and the (SU(2) x U(1))(1) x (SU(2) x U(1)) gauge group versions of the LH model. We also show that the Goldstone bosons present in the model do not contribute to the effective potential at the one-loop level. Finally, by neglecting the contribution of higher dimensional operators, we discuss the restrictions that the new one-loop contributions set on the parameter space of the LH model and the need to include higher loop corrections to the Higgs potential., DGICYT (Spain), Instituto de Física Corpuscular, Valencia, FPU grant from the Spanish M.E.C., Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2000 The American Physical Society. We acknowledge partial support from the Spanish Ministerio de Educación y Ciencia under CICYT projects AEN97-1693 and AEN97-1678. E.R.M. also acknowledges support from the Spanish AME Foundation., We present a unified analysis of the two main production processes of vector boson pairs at the CERN LHC, VV-fusion and q (q) over bar annihilation, in a minimal strongly interacting electroweak symmetry breaking sector. Using a unitarized electroweak chiral Lagrangian formalism and modeling the final VLVL strong rescattering effects by a form factor, we describe q (q) over bar annihilation processes in terms of the two chiral parameters that govern elastic VLVL scattering. Depending on the values of these two chiral parameters, the unitarized amplitudes may present resonant enhancements in different angular momentum-isospin channels. Scanning this two parameter space, wt: generate the general resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector and determine the regions that can be probed at the CERN LHC., Spanish Ministerio de Educación y Ciencia, under CICYT Project, Spanish AME Foundation, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 1997 The American Physical Society I would like to thank the Theory Group at Berkeley for their kind hospitality and the Jaime del Amo Foundation for financial support. I have also greatly appreciated the patience of M. Suzuki during his explanations and discussions on the unphysical poles. I am also indebted to R.S. Chivukula for his comments on models with I52 resonances. This work has been partially supported by the Ministerio de Educación y Ciencia (Spain) (Grant No. CICYT AEN93-0776). Partial support by U.S. DOE under Contract No. DE-AC03-76SF00098 is gratefully acknowledged., Within the chiral Lagrangian formalism it is possible to describe the general strongly coupled symmetry-breaking sector in terms of a few parameters. Based on a dispersive approach we study the resonance spectrum up to 3 TeV in chiral parameter space. This procedure could also be useful to extract higher energy resonant behavior from low-energy collider data. It is also shown how the method reproduces the correct pole structure of resonances as well as other analytic features. The results also hint at a possible excluded region of parameter space., Ministerio de Educación y Ciencia (Spain), U.S. DOE, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub