4,351 research outputs found
Pion production in nonequilibrium Chiral perturbation Theory
We apply the formalism of Chiral Perturbation Theory out of thermal
equilibrium to describe explosive production of pions via the parametric
resonance mechanism. To lowest order the lagrangian is that of the Nonlinear
Sigma Model where the pion decay constant becomes a time-dependent function.
This model alows for a consistent nonequilibrium formulation within the
framework of the closed time path method, where one-loop effects can be
systematically accounted for and renormalized. We work in the narrow resonance
regime where there is only one resonant band. The present approach is limited
to remain below the back-reaction time, although it accounts for nearly all the
pion production during the typical plasma lifetime. The space and time
components of the pion decay constant are also analyzed.Comment: 23 pages, 8 figures, RevTe
Light meson resonances from unitarized Chiral Perturbation Theory
We report on our recent progress in the generation of resonant behavior in
unitarized meson-meson scattering amplitudes obtained from Chiral Perturbation
Theory. These amplitudes provide simultaneously a remarkable description of the
resonance region up to 1.2 GeV as well as the low energy region, since they
respect the chiral symmetry expansion. By studying the position of the poles in
these amplitudes it is possible to determine the mass and width of the
associated resonances, as well as to get a hint on possible classification
schemes, that could be of interest for the spectroscopy of the scalar sector.Comment: Invited talk to the II International Workshop on Hadron Physics &
Effective Theories of Low Energy QCD. 25-29 September 2002. Coimbra. Portuga
Meson resonances from unitarized meson scattering at one loop in Chiral Perturbation Theory
We show the results for the scattering poles associated to the rho, f0, a0,
K*, sigma and kappa resonances in meson-meson scattering. Our amplitudes are
obtained from the complete one-loop meson-meson scattering amplitudes from
Chiral Perturbation Theory. Once unitarized with the Inverse Amplitude Method,
they describe remarkably well the data simultaneously in the low energy and
resonance regions up to 1.2 GeV, using low energy parameters compatible with
present determinations.Comment: To appear in the proceedings of the 5th International Conference on
``Quark confinement and the hadron spectrum'', held in Gargnano, Garda Lake,
Italy. 10-14th September 2002. 3 page
Unitarization of the complete meson-meson scattering at one loop in Chiral Perturbation Theory
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.Comment: To appear in the proceedings of QCD@work: International Workshop on
QCD: Theory and Experiment. Martina Franca (Italy) June 16-20. 200
Electromagnetic fields and transport coefficients in a hot pion gas
We present recent results on finite temperature electromagnetic form factors
and the electrical conductivity in a pion gas. The standard Chiral Perturbation
Theory power counting needs to be modified for transport coefficients. We pay
special attention to unitarity and to possible applications for dilepton and
photon production.Comment: 4pp, 2 figures, talk given at "Strong and Electroweak Matter 2006",
BNL, May 200
Complete meson-meson scattering within one loop in Chiral Perturbation Theory: Unitarization and resonances
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.Comment: 4 pages, To appear in the Proceedings of the IX International
Conference on Hadron Spectroscopy, HADRON2001, IHEP, Protvino, Russia, August
200
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