Person: Llanes Estrada, Felipe José
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 128
PublicationTop-antitop production from W_(L)^(+)W_(L)^(-) and Z_(L)_Z(L) scattering under a strongly interacting symmetry-breaking sector(Springer, 2017-07-01) Castillo, Andrés; Delgado López, Rafael; Dobado González, Antonio; Llanes Estrada, Felipe JoséBy considering a non-linear electroweak chiral Lagrangian, including the Higgs, coupled to heavy quarks, and the equivalence theorem, we compute the one-loop scattering amplitudes W^(+)W^(−) → tṫ, Z Z → tṫ and hh → tṫ (in the regime M^(2)_(t)/v^(2) « √sM_(t)/v^(2) « s/v^(2) and to NLO in the effective theory). We calculate the scalar partial-wave helicity amplitudes which allow us to check unitarity at the perturbative level in both M_(t) /v and s/v. As with growing energy perturbative unitarity deteriorates, we also introduce a new unitarization method with the right analytical behavior on the complex s-plane and that can support poles on the second Riemann sheet to describe resonances in terms of the Lagrangian couplings. Thus we have achieved a consistent phenomenological description of any resonant tṫ production that may be enhanced by a possible strongly interacting electroweak symmetry breaking sector. PublicationUnbiased interpolated neutron-star EoS at finite T for modified gravity studies(Springer, 2022-01-20) Lope Oter, Eva; Llanes Estrada, Felipe JoséNeutron stars and their mergers provide the highest-density regime in which Einstein's equations in full (with a matter source) can be tested against modified theories of gravity. But doing so requires a priori knowledge of the Equation of State from nuclear and hadron physics, where no contamination from computations of astrophysics observables within General Relativity has been built in. We extend the nEoS uncertainty bands, useful for this very purpose, to finite (but small) temperatures up to T = 30 MeV, given that the necessary computations in ChPT and in pQCD are already available in the literature. The T-dependent band boundaries will be provided through the COMPOSE repository and our own website. PublicationViscosity of meson matter(American Physical Society, 2004-06) Dobado González, Antonio; Llanes Estrada, Felipe JoséWe 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. PublicationLHC@Complutense. Análisis de datos de física de altas energías en el Grado en Física y el Máster en Física Teórica.(2016-01-29) Llanes Estrada, Felipe JoséResumo las actividades encuadradas dentro de este pequeño proyecto que tienen como objetivo revitalizar la docencia en física de partículas elementales. PublicationNonordinary light meson couplings and the 1/N_c expansion(American Physical Society, 2014-08-14) Cohen, Thomas; Llanes Estrada, Felipe José; Peláez Sagredo, José Ramón; Ruiz de Elvira Carrascal, JacoboWe study the large N_c behavior of couplings among light meson states with different compositions in terms of quarks and gluons. We shortly review the most common compositions of mesons, which are of interest for the understanding of low-lying meson resonances, namely, the ordinary quark-antiquark states as well as the nonordinary glueball, tetraquark, and other states. We dedicate special attention to Jaffe's generalization of the tetraquark with N_c - 1 q -q over bar q pairs, which is the only type of state we have identified whose width does not necessarily vanish with N_c, though it does decouple exponentially with N_c from the ππ channel, so that it is weakly coupled to the meson-meson system. PublicationThe ratio of viscosity to entropy density in a pion gas satisfies the KSS holographic bound(Springer, 2007-03) Dobado González, Antonio; Llanes Estrada, Felipe JoséWe evaluate the ratio of shear viscosity to entropy density in a pion gas employing the Uehling-Uehlenbeck equation and experimental phase-shifts parameterized by means of the SU(2) inverse amplitude method. We find that the ratio for this monocomponent gas stays well above the KSS 1/(4 pi) bound. We find similar results with other sets of phase-shifts and conclude that the bound is nowhere violated. PublicationQuark mass dependence of the pion vector form factor(Elsevier Science BV, 2009-07-06) Llanes Estrada, Felipe José; Feng Kun, Guo; Hanhart, ChristophWe examine the quark mass dependence of the pion vector form factor, particularly the curvature (mean quartic radius). We focus our study on the consequences of assuming that the coupling constant of the ρ to pions, gρππ , is largely independent of the quark mass while the quark mass dependence of the ρ mass is given by recent lattice data. By employing the Omnès representation we can provide a very clean estimate for a certain combination of the curvature and the square radius, whose quark mass dependence could be determined from lattice computations. This study provides an independent access to the quark mass dependence of the ρππ coupling and in this way a non-trivial check of the systematics of chiral extrapolations. We also provide an improved value for the curvature for hysical values for the quark masses, namely (r(4)) = 0.73±0.09 fm(4) or equivalently c(V) = 4.00±0.50 GeV(−4). PublicationSpontaneous mass generation and the small dimensions of the Standard Model gauge groups U(1), SU(2) and SU(3)(vol 915, pg 262, 2017)(Erratum)(Elsevier, 2019-12) García Fernández, Guillermo; Guerrero Rojas, Jesús; Llanes Estrada, Felipe JoséWe point out an error in our previous work, that affects the claims made for the special Lie groups and for the SO(N-c) groups of lowest dimension, which are therefore retracted. Our earlier results stand for larger-dimension SO(N-c), as well as for Sp(N-c) and SU(N-c) classical Lie groups. (C) 2016 The Author(s). Published by Elsevier B.V. PublicationStrongly interacting WLWL, Z(L)Z(L) and hh from unitarized one-loop computations(Elsevier Sciende BV, 2016-04) Delgado López, Rafael; Dobado González, Antonio; Llanes Estrada, Felipe JoséRecently, a new boson h has been discovered at the LHC which, so far, is compatible with the properties of the SM Higgs. However, the SM is not the most general low-energy dynamics for the minimal electroweak symmetry breaking sector with three Goldstone bosons and one light scalar. By using non-linear effective Lagrangian for these four particles we study different processes at one-loop precision, identifying the counterterms needed to cancel the divergences. Then we apply the IAM unitarization method on the partial waves, both to make more realistic predictions which could be tested at the LHC and to discuss the limitations of the one-loop computations. The studied processes are the elastic scattering amplitude for both the longitudinal components of the gauge bosons V = W, Z and the hh → hh, as well as the inelastic VV → hh. PublicationMixing and m(q) dependence of axial vector mesons in the Coulomb gauge QCD model.(Amer Physical Soc, 2019-12-17) Abreu, Luciano M.; Favero, Aline G.; Llanes Estrada, Felipe José; García Sanchez, AlejandroWe discuss pure q (q) over bar axial-vector mesons in the Tamm-Dancoff approximation of the Coulomb-gauge QCD model from North Carolina State University. While recent studies have put emphasis in configuration mixing with open meson-meson channels, we here concentrate on the simpler closed-channel problem and follow the 1(+) mixing through a wide range of quark masses. We also examine their radial excitations and discuss with them the concept of insensitivity to chiral symmetry breaking.