arXiv subjects
Publications and source records attributed to J. R. Pelaez.
The evolution of the chiral condensate with the temperature is studied using SU(3) Chiral Perturbation Theory and the virial expansion. We observe a large decrease of the melting temperature of the non-strange condensate compared with the SU(2) case. Due to the larger mass of the strange quark we also find an slower temperature evolution of the strange condensate compared with the non-strange condensate.
The temperature evolution of the chiral condensates in a gas made of pions, kaons and etas is studied within the framework of SU(2) and SU(3) Chiral Perturbation Theory. We describe the temperature dependence of the quark condensates by using the meson meson scattering phase shifts in a second order virial expansion. We find that the SU(3) formalism yields an extrapolated melting temperature for the non-strange condensates which is lower by about 20-30 MeV than within SU(2). In addition our results show that the strange condensate melting is slower than that of the non-strange, due to the different strange and non-strange quark masses.
We study the temperature evolution of the rho and sigma mass and width, using a unitary chiral approach. The one-loop pion-pion scattering amplitude in Chiral Perturbation Theory at finite temperature 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 rho-pion-pion coupling increases. The rho behavior seems to be favored by experimental results. In the sigma case, it signals chiral symmetry restoration.
The SU(2) and SU(3) chiral phase transitions in a hot gas made of pions, kaons and etas are studied within the framework of Chiral Perturbation Theory. By using the meson meson scattering phase shifts in a second order virial expansion, we are able to describe the temperature dependence of the quark condensates. We have estimated the critical temperatures where the different condensates melt. In particular, the SU(3) formalism yields a lower critical temperature for the non-strange condensates than within SU(2), and also suggests that the strange condensate may melt at a somewhat higher temperature, due to the different strange and non-strange quark masses.
Within Chiral Perturbation Theory, we study elastic pion scattering in the I=0, J=2, channel, whose main features are the f2(1270) resonance and the vanishing of the lowest order. By means of a chiral model that includes an explicit resonance coupled to pions, we describe the data and calculate the resonance contribution to the O(p^4) and O(p^6) chiral parameters. We also generalize the Inverse Amplitude Method to higher orders, which allows us to study channels with vanishing lowest order. In particular, we apply it to the I=0,J=2 case, finding a good description of the f2(1270) resonance, as a pole in the second Riemann sheet.
We present the complete one-loop calculation of all the two meson scattering amplitudes within the framework of SU(3) Chiral Perturbation Theory, which includes pions, kaons and the eta. In addition, we have unitarized these amplitudes with the coupled channel Inverse Amplitude Method, which ensures simultaneously the good low energy properties of Chiral Perturbation Theory and unitarity. We show how this method provides a remarkable description of meson-meson scattering data up to 1.2 GeV including the scattering lengths and the generation of seven light resonances, which is consistent with previous determination of the chiral parameters. Particular attention is paid to discuss the differences and similarities of this work with previous analysis in the literature.
We review our recent one-loop calculation of all the two meson scattering amplitudes within SU(3) Chiral Perturbation Theory, i.e. with pions, kaons and etas. By unitarizing these amplitudes we are able to generate dynamically the lightest resonances in meson-meson scattering. We thus obtain a remarkable description of the meson-meson scattering data right from threshold up to 1.2 GeV, in terms of chiral parameters in good agreement with previous determinations.
We report on our one-loop calculation of all the two meson scattering amplitudes within SU(3) Chiral Perturbation Theory, i.e. with pions, kaons and etas. Once the amplitudes are unitarized with the coupled channel Inverse Amplitude Method, they satisfy simultaneously the correct low-energy chiral constraints and unitarity. We obtain a remarkable description of meson-meson scattering data up to 1.2 GeV including the scattering lengths and seven light resonances.
We review our results on the calculation of helicity 1/2 gravitino production during preheating. The method we present is based on the equivalence between goldstinos and longitudinal gravitinos at high energies. The problem is thus reduced to the standard (Majorana) fermion production after inflation. Comparison between helicity 3/2 and 1/2 production and with the results obtained in the unitary gauge is also presented.
Starting from the Chiral Perturbation Theory Lagrangian, but keeping different masses for the charged and neutral mesons, and using a previously developed non-perturbative unitary scheme that generates the lightest meson-meson resonances, we construct K Kbar to K Kbar and K Kbar to pi+ pi- in the vector channel. This allows us to obtain the kaon-loop contribution to the phi-rho mixing and study the phi to pi+pi- decay. The dominant contribution to this decay comes from the phi to gamma to pi+pi- process. However, there can be large interferences with the subdominant contributions coming from phi-rho and phi-omega mixing, or of these two contributions among themselves. As a consequence, a reliable measurement of phi to pi+pi- decay could be used to differentiate between some phi-omega mixing scenarios proposed in the literature.
We present a unified analysis of the two main production processes of vector boson pairs at the LHC, VV-fusion and qqbar annihilation, in a minimal strongly interacting electroweak symmetry breaking sector. Using a unitarized electroweak chiral Lagrangian formalism and modeling the final V_L V_L strong rescattering effects by a form factor, we describe qqbar annihilation processes in terms of the two chiral parameters that govern elastic V_L V_L 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, we generate the general resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector and determine the regions that can be probed at the LHC.
We study the high-energy equivalence between helicity 1/2 gravitinos and goldstinos in order to calculate the production of gravitinos in time-dependent scalar and gravitational backgrounds. We derive this equivalence for equations of motion, paying attention to some subtleties, mainly due to external sources, that are not present in the standard proofs. We also propose the Landau gauge as a simplifying alternative to the usual gauge choices, both for practical calculations and in the equivalence theorem proof.
By means of the Inverse Amplitude Method we unitarize the elastic pion-nucleon scattering amplitudes obtained from Heavy Baryon Chiral Perturbation Theory to O(q^3). Within this approach we can enlarge their applicability range and generate the Delta(1232) resonance. We can find a reasonable description of the pion nucleon phase shifts with (q^2) parameters in agreement with the resonance saturation hypothesis. However, the uncertainties in the analysis of the low energy data as well as the large number of chiral parameters, which can have strong correlations, allow us to obtain very good fits with rather different sets of chiral constants.
We present a new technique for the calculation of helicity $\pm 1/2$ gravitino production during preheating. It is based on the equivalence between goldstinos and helicity $\pm 1/2$ gravitinos at high energies. The problem is thus reduced to the standard (Majorana) fermion production after inflation. Comparison with the results obtained in the unitary gauge is also presented.
We report on recent results on the decay of the phi into pi^+ pi^- and phi radiative decays into pi^0 pi^0 gamma and pi^0 eta gamma, which require the consideration of the final state interaction of a pair of mesons in a region inaccessible to Chiral Perturbation Theory. By using nonperturbative chiral unitary methods for the meson meson interaction we can obtain the corresponding decay widths and the results are compared with recent experimental data.
By means of a coupled channel non-perturbative unitary approach, it is possible to extend the strong constrains of Chiral Perturbation Theory to higher energies. In particular, it is possible to reproduce the lowest lying resonances in meson-meson scattering up to 1.2 GeV using the parameters of the O(p^2) and O(p^4) Chiral Lagrangian. The meson baryon sector can also be tackled along similar lines. We report on an update of these results showing some examples of photon induced reactions where the techniques have been recently applied.
We report on our present work, where by means of the Inverse Amplitude Method we unitarize the elastic pion nucleon scattering amplitudes of Heavy Barion Chiral Perturbation Theory at O(q^3). We reproduce the scattering up to the inelastic thresholds including the Delta(1232) resonance. The fitted chiral constants are rather different from those obtained by fitting the extrapolated threshold parameters for the non-unitarized theory.