Related papers: Pion-delta sigma-term
We have reanalyzed the $\pi ^{\pm} p$ scattering data at low energy in the Coulomb-nuclear interference region as measured by the CHAOS group at TRIUMF with the aim to determine the pion-nucleon $\sigma$ term. The resulting value…
The multipole amplitudes for the N - Delta electromagnetic transition are computed in the framework of the linear sigma model and the chiral chromodielectric model for small and moderate photon virtualities. The models include quark and…
CERN measurements of pi(-)p->pi(-)pi(+)n on polarized target at 17.2 GeV/c enable experimental determination of partial wave production amplitudes below 1080 MeV. The measured S-wave transversity amplitudes provide evidence for a narrow…
Employing a symmetry-preserving contact-interaction formulation of the Dyson-Schwinger equations in quantum chromodynamics (QCD), we examine the identity of the $\sigma$ meson and its implications for the gravitational structure of hadrons.…
We investigate the neutral pion photoproduction on the proton near threshold in covariant chiral perturbation theory with the explicit inclusion of Delta degrees of freedom. This channel is specially sensitive to chiral dynamics and the…
We describe the pion electroproduction processes in the $\Delta$(1232)-resonance region within the framework of chiral effective-field theory. By studying the observables of pion electroproduction in a next-to-leading order calculation we…
A calculation of the pion-production operator up to next-to-next-to-leading order for s-wave pions is performed within chiral effective field theory. In the previous study [Phys. Rev. C 85, 054001 (2012)] we discussed the contribution of…
Within a chiral quark sigma model in which quarks interact via the exchange of sigma and pi-mesons, hadron properties are investigated. This model of the nucleon and delta is based on the idea that strong QCD forces on very short distances…
Using dispersive representations of the nucleon gravitational form factors, the results for their absorptive parts from chiral effective field theory in curved space-time, and the mechanical stability conditions, we obtain a model…
After giving brief discussions on the chiral condensate in hot and/or dense hadronic matter and the significance of the $\sigma$ meson in QCD, we discuss the importance of experiments using nuclear targets including ones with…
We study the effects of the $\Delta$(1232) resonance as an effective degree of freedom for charged and neutral pion photo-production on nucleons. Different observables have been calculated for these processes by using relativistic chiral…
The neutrino pion production off the nucleon is traditionally described in the literature by means of the weak excitation of the Delta(1232) resonance and its subsequent decay into N pi. Here, we present results from a model that includes…
We present an extraction of the pion-nucleon ($\pi N$) scattering lengths from low-energy $\pi N$ scattering, by fitting a representation based on Roy-Steiner equations to the low-energy data base. We show that the resulting values confirm…
We discuss an on-shell approach to pion-nucleon physics that is consistent order by order in a $1/f_{\pi}$ expansion with the chiral reduction formula, crossing, and relativistic unitarity. A number of constraints between the on-shell…
We generalize the linear sigma model in order to develop a chiral-invariant model of nuclear structure. The model is natural, and contains not only the usual sigma meson which is the chiral partner of the pion but also a new chiral-singlet…
Chiral properties of positive and negative parity nucleons, N and N*$, are studied from the viewpoint of chiral symmetry. Two possible ways to assign chiral transformations to the negative parity nucleon are considered. Using linear sigma…
We study the chiral symmetry structure in a linear sigma model with fermions in the presence of an external, uniform magnetic field in the 'effective potential' approach at the one loop level. We also study the chiral phase transition as a…
The quark-level linear sigma model is revisited, in particular concerning the identification of the f_0(400-1200) (or \sigma(600)) scalar meson as the chiral partner of the pion. We demonstrate the predictive power of the linear sigma model…
We calculate the neutral pion photoproduction on the proton near threshold in covariant baryon chiral perturbation theory, including the $\Delta(1232)$ resonance as an explicit degree of freedom, up to chiral order $p^{7/2}$ in the $\delta$…
The nuclear sigma term is calculated including the nuclear matrix element of the derivative of the NN interaction with respect to the quark mass, $m_q\frac{\partial V_{NN}}{\partial m_q}$. The NN potential is evaluated in the…