Search results for "Chiral symmetry"

Erratum to: “Low lying S=−1 excited baryons and chiral symmetry”

2002

Chiral Symmetry And Low Energy Pion Photoproduction

1992

The low energy theorem based on chiral symmetry for the photoproduction of neutral pions from proton at threshold is reviewed in the light of recent experimental results from Saclay and Mainz. There is no appreciable disagreement at threshold but the energy dependence of the threshold amplitude remains unexplained. A critique of the assumptions made in deriving low energy theorems by various methods is presented.

Bag models and hadron structure

2008

We review the fundamental ideas leading to the basic assumptions behind the bag model description of hadron structure and explore in some detail the so called MIT bag model. We discuss the relevance of chiral symmetry and incorporate it in a bag model scheme by adding a pion field. We show perturbative techniques of calculating gluonic and pionic effects. We discuss the consequences of the solitonic nature of the hedgehog solution of the pion field and introduce the skyrmion bag model. We end up by drawing some conclusions of our study and discussing recent developments in this area.

Chiral expansion of the nucleon mass to order q^6

2006

We present the results of a complete two-loop calculation at order q^6 of the nucleon mass in manifestly Lorentz-invariant chiral perturbation theory. The renormalization is performed using the reformulated infrared renormalization, which allows for the treatment of two-loop integrals while preserving all relevant symmetries, in particular chiral symmetry.

The role of resonances in chiral perturbation theory

1989

32 páginas, 2 figuras, 5 tablas.-- BUTP-88-18 ; CERN-TH-5185-88 ; CPT-2158 ; UWTHPH-1988-29.

In-medium pi-pi Correlation Induced by Partial Restoration of Chiral Symmetry

2000

We show that both the linear and the non-linear chiral models give an enhancement of the pi-pi cross section near the 2pi threshold in the scalar-iso-scalar (I=J=0) channel in nuclear matter. The reduction of the chiral condensate, i.e., the partial chiral restoration in nuclear matter, is responsible for the enhancement in both cases. We extract an effective 4pi-nucleon vertex which is responsible for the enhancement but has not been considered in the non-liear models for in-medium pi-pi interaction. Relation of this vertex and a next-to-leading order terms in the heavy-baryon chiral lagrangian, L_piN^(2), is also discussed.

ChPT parameters from tau-decay data

2015

Using the updated ALEPH V-A spectral function from tau decays, we determine the lowest spectral moments of the left-right correlator and extract dynamical information on order parameters of the QCD chiral symmetry breaking. Uncertainties associated with violations of quark-hadron duality are estimated from the data, imposing all known short-distance constraints on a resonance-based parametrization. Employing proper pinched weight functions, we obtain an accurate determination of the effective chiral couplings L10 and C87 and the dimension-six and -eight contributions in the Operator Product Expansion.

Excited charmed mesons in chiral perturbation theory

1992

Abstract Heavy meson, p- to s-wave, one-pion transitions are studied in the context of the union of heavy quark and chiral symmetries. The interactions are described by an effective lagrangian density invariant under the combined heavy quark and chiral symmetries. We study the pattern of the heavy quark symmetry breaking by considering 1 m Q corrections to the infinite mass limit.

Chiral symmetry and pi-pi scattering in the Covariant Spectator Theory

2014

The pi-pi scattering amplitude calculated with a model for the quark-antiquark interaction in the framework of the Covariant Spectator Theory (CST) is shown to satisfy the Adler zero constraint imposed by chiral symmetry. The CST formalism is established in Minkowski space and our calculations are performed in momentum space. We prove that the axial-vector Ward-Takahashi identity is satisfied by our model. Then we show that, similar to what happens within the Bethe-Salpeter formalism, application of the axial-vector Ward-Takahashi identity to the CST pi-pi scattering amplitude allows us to sum the intermediate quark-quark interactions to all orders. The Adler self-consistency zero for pi-pi…

Chiral symmetry breaking condensates from baryonic sum rules

1984

We analyse baryonic sum rules in order to determine chiral symmetry breaking condensates. We especially investigate the influence of the choice of the interpolating field and of the factorization hypothesis for the four quark condensate. Our results are consistent with those obtained from pseudoscalar sum rules and PCAC.