Search results for "CHIRAL SYMMETRY"

Power counting in baryon chiral perturbation theory including vector mesons

2003

It is demonstrated that using a suitable renormalization condition one obtains a consistent power counting in manifestly Lorentz-invariant baryon chiral perturbation theory including vector mesons as explicit degrees of freedom.

Pion production in deeply virtual Compton scattering

2003

Using a soft pion theorem based on chiral symmetry and a $\Delta(1232)$ resonance model we propose an estimate for the production cross section of low energy pions in the deeply virtual Compton scattering (DVCS) process. In particular, we express the $e p \to e \gamma \pi N$ processes in terms of generalized parton distributions. We provide estimates of the contamination of the $e p \to e \gamma p$ DVCS observables due to this associated pion production processes when the experimental data are not fully exclusive, for a set of kinematical conditions representative of present or planned experiments at JLab, HERMES and COMPASS.

Chiral symmetry and meson exchange approach to hypernuclear decay

2000

We take an approach to the $\Lambda$ nonmesonic weak decay in nuclei based on the exchange of mesons under the guidelines of chiral Lagrangians. The one pion and one kaon exchange are considered, together with the exchange of two pions, either correlated, leading to an important scalar-isoscalar exchange ($\sigma$-like exchange), or uncorrelated (box diagrams). A drastic reduction of the OPE results for the $\Gamma_n/\Gamma_p$ ratio is obtained and the new results are compatible with all present experiments within errors. The absolute rates obtained for different nuclei are also in fair agreement with experiment.

NEUTRINO-INDUCED WEAK PION PRODUCTION OFF THE NUCLEON

2008

We study neutrino induced one-pion production off the nucleon in and around the Delta resonance region. Apart from the Delta-pole mechanism we include background terms required by chiral symmetry. These background terms give sizeable contributions in all channels. To better reproduce the ANL $q^2$-differential cross section data, we make a new fit of the $C_5^A(q^2)$ axial nucleon to Delta form factor. The new result $C_5^A(0)=0.867\pm 0.075$ is some 30% smaller than the commonly accepted value. This correction is compatible with most quark model estimates and a recent lattice calculation

Meson-meson interactions in a nonperturbative chiral approach

1999

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 …

Dynamical Symmetry Breaking in Warped Compactifications

2001

We study dynamical electroweak symmetry breaking in the Randall-Sundrum scenario. We show that one extra dimension is enough to give the correct pattern of electroweak symmetry breaking in a simple model with gauge bosons and the right-handed top quark in the bulk. The top quark mass is also in agreement with experiment. Furthermore, we propose an extended scenario with all Standard Model gauge bosons and fermions propagating in the bulk, which naturally accommodates the fermion mass hierarchies. No new fields or interactions beyond the observed in the Standard Model are required.

A consistent study of the the low energy baryon spectrum and the nucleon-nucleon interaction within the chiral quark model

1995

By solving the Schr\"{o}dinger equation for the three-quark system in the hyperspherical harmonic approach, we have studied the low energy part of the nucleon and $\Delta$ spectra using a quark-quark interaction which reproduces the nucleon-nucleon phenomenology. The quark-quark hamiltonian considered includes, besides the usual one-gluon exchange, pion and sigma exchanges generated by the chiral symmetry breaking. The baryonic spectrum obtained is reasonable and the resulting wave function gives consistency to the ansatz used in the two baryon system.

Heavy Resonances in the Electroweak Effective Lagrangian

2015

As a first step towards the construction of a general electroweak effective Lagrangian incorporating heavy states, we present here a simplified version where only vector and axial-vector spin-1 triplets are involved. We adopt an effective field theory formalism, implementing the electroweak chiral symmetry breaking SU(2)L x SU(2)R -> SU(2)L+R, which couples the heavy states to the SM fields. At low energies, the heavy degrees of freedom are integrated out from the action and their effects are hidden in the low-energy couplings of the Electroweak Effective Theory, which can be tested experimentally. Short-distance constraints are also implemented, requiring a proper behaviour in the high-…

Erratum to: Chiral-symmetry restoration in clustered hadronic matter

2004

Baryonic resonances from baryon decuplet-meson octet interaction

2004

We study $S$-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons using the lowest order chiral Lagrangian. In the S=1 sector, we find an attractive interaction in the $\Delta K$ channel with I=1 while it is repulsive for I=2. The attractive interaction leads to a pole in the second Riemann sheet of the complex plane and is manifested as a large strength in the scattering amplitude close to the $\Delta K$ threshold, which is not the case for I=2. We use the unitarized coupled channel approach to also investigate all the other possible values of strangeness and isospin. We find two bound states in the SU(3) limit corresponding to the octet and decuplet representatio…