39 research outputs found
Resonances, Chiral Symmetry, Coupled Channel Unitarity and Effective Lagrangians
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. We report on an update of these results
examining their possible relevance for meson spectroscopy.Comment: To appear in the proceedings of the 8th International Conference on
Hadron Spectroscopy, HADROn 99, August 24-28, 1999, Beijing, China. Four
pages, uses espcrc1.sty (included
LHC sensitivity to the resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector
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.Comment: Final version to appear in Phys. Rev. D, including a more detailed
exposition and a few more references. Conclusions and results unchanged. 14
pages, 5 figure
Chiral Perturbation Theory and the f2(1270) resonance
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.Comment: 4 pages,1 figur
The SU(2) and SU(3) chiral phase transitions within Chiral Perturbation Theory
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.Comment: 4 pages, two figures. Final version to appear in Phys Rev D. Complete
model independent calculation. Unitarized ChPt only used to check
extrapolation at high T. References added and numerical bug correcte
Chiral Symmetry and light resonances in hot and dense matter
We present a study of the scattering amplitude in the and
channels at finite temperature and nuclear density within a chiral
unitary framework. Meson resonances are dynamically generated in our approach,
which allows us to analyze the behavior of their associated scattering poles
when the system is driven towards chiral symmetry restoration. Medium effects
are incorporated in three ways: (a) by thermal corrections of the unitarized
scattering amplitudes, (b) by finite nuclear density effects associated to a
renormalization of the pion decay constant, and complementarily (c) by
extending our calculation of the scalar-isoscalar channel to account for finite
nuclear density and temperature effects in a microscopic many-body
implementation of pion dynamics. Our results are discussed in connection with
several phenomenological aspects relevant for nuclear matter and Heavy-Ion
Collision experiments, such as mass scaling vs broadening from dilepton
spectra and chiral restoration signals in the channel. We also
elaborate on the molecular nature of resonances.Comment: 14 pages, 14 figures. Contribution to Hard Probes 2008, Illa de A
Toxa, Spain, June 8th-14th 200
Photoproduction of meson and baryon resonances in a chiral unitary approach
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.Comment: Contribution to the Erice Summer School of Nuclear Physics, 21th
course: Electromagnetic Probes and the Structure of Hadrons and Nuclei
September 17th - 25th, 1999, Erice/Sicily/Ital
Thermal rho and sigma mesons from chiral symmetry and unitarity
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.Comment: 5 pages, 5 figures, revtex. References and brief comments added.
Final version to appear in Phys. Rev.
Chiral dynamics in U(3) unitary chiral perturbation theory
We perform a complete one-loop calculation of meson-meson scattering, and of
the scalar and pseudoscalar form factors in U(3) chiral perturbation theory
with the inclusion of explicit resonance fields. This effective field theory
takes into account the low-energy effects of the QCD U_A(1) anomaly explicitly
in the dynamics. The calculations are supplied by non-perturbative
unitarization techniques that provide the final results for the meson-meson
scattering partial waves and the scalar form factors considered. We present
thorough analyses on the scattering data, resonance spectroscopy, spectral
functions, Weinberg-like sum rules and semi-local duality. The last two
requirements establish relations between the scalar spectrum with the
pseudoscalar and vector ones, respectively. The Nc extrapolation of the various
quantities is studied as well. The fulfillment of all these non-trivial aspects
of the QCD dynamics by our results gives a strong support to the emerging
picture for the scalar dynamics and its related spectrum.Comment: To match the version accepted by Phys.Lett.
Recent progress on the chiral unitary approach to meson meson and meson baryon interactions
We report on recent progress on the chiral unitary approach, analogous to the
effective range expansion in Quantum Mechanics, which is shown to have a much
larger convergence radius than ordinary chiral perturbation theory, allowing
one to reproduce data for meson meson interaction up to 1.2 GeV. Applications
to physical processes so far unsuited for a standard chiral perturbative
approach are presented. Results for the extension of these ideas to the meson
baryon sector are discussed, together with applications to kaons in a nuclear
medium and atoms.Comment: Contribution to the KEK Tanashi Symposium on Physics of Hadrons and
Nuclei, Tokyo, December 1998, 10 pages, 3 postscript figures. To be published
as a special issue of Nuclear Physics
Meson-meson interactions in a nonperturbative chiral approach
A non-perturbative method which combines constraints from chiral symmetry breaking and coupled channel unitarity is used to describe the meson-meson interaction up to about 1.2 GeV. The approach uses the O(p^2) and O(p^4) chiral Lagrangians. The seven free parameters of the O(p^4) Lagrangian are fitted to the data. The results are in good agreement with a vast amount of experimental analyses. The amplitudes develop poles in the complex plane corresponding to the f0, a0, rho, K*, phi, sigma and kappa resonances; the latter two, very broad. The total and partial decay widths of the resonances are also well reproduced. Further extensions and applications of this chiral non-perturbative scheme are also discussed