K. Pumsa-ard

Magnetic moments of heavy baryons in the relativistic three-quark model

The magnetic moments of ground state single, double and triple heavy baryons containing charm or bottom quarks are calculated in a relativistic three-quark model, which, in the heavy-quark limit, is consistent with heavy-quark effective theory and heavy hadron chiral perturbation theory. The internal quark structure of baryons is modeled by baryonic three-quark currents with a spin-flavor structure patterned according to standard covariant baryonic wave functions and currents used in QCD sum rule calculations.

Light baryon magnetic moments and N ->Delta gamma transition in a Lorentz covariant chiral quark approach

We calculate magnetic moments of light baryons and N{yields}{delta}{gamma} transition characteristics using a manifestly Lorentz covariant chiral quark approach for the study of baryons as bound states of constituent quarks dressed by a cloud of pseudoscalar mesons.

Electromagnetic form factors of the baryon octet in the perturbative chiral quark model

Abstract.We apply the perturbative chiral quark model at one loop to analyze the electromagnetic form factors of the baryon octet. The analytic expressions for baryon form factors, which are given in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion decay constant, axial nucleon coupling, strong pion-nucleon form factor), and the numerical results for baryon magnetic moments, charge and magnetic radii are presented. Our results are in good agreement with experimental data.

Axial form factor of the nucleon in the perturbative chiral quark model

We apply the perturbative chiral quark model (PCQM) at one loop to analyse the axial form factor of the nucleon. This chiral quark model is based on an effective Lagrangian, where baryons are described by relativistic valence quarks and a perturbative cloud of Goldstone bosons as dictated by chiral symmetry. We apply the formalism to obtain analytical expressions for the axial form factor of the nucleon, which is given in terms of fundamental parameters of low-energy pion–nucleon physics (weak pion decay constant, strong pion–nucleon form factor) and of only one model parameter (radius of the nucleonic three-quark core).

Nucleon polarizabilities in the perturbative chiral quark model

The nucleon polarizabilities alpha E and beta m are studied in the context of the perturbative chiral quark model. We demonstrate that meson-cloud effects are sufficient to explain the electric polarizability of the nucleon. Contributions of excited quark states to the paramagnetic polarizability are dominant and cancel the diamagnetic polarizability arising from the chiral field. The obtained results are compared to data and other theoretical predictions.

Strong CP violation and the neutron electric dipole form factor

We calculate the neutron electric dipole form factor induced by the CP-violating θ term of QCD within a perturbative chiral quark model which includes pion and kaon clouds. On this basis, we derive the neutron electric dipole moment and the electron—neutron Schiff moment. From the existing experimental upper limits on the neutron electric dipole moment, we extract constraints on the θ parameter and compare our results with other approaches.

Chiral Dynamics of Baryons in the Quark Model

We discuss recent applications of the perturbative chiral quark model (PCQM) in the analysis of the structure of baryons. The PCQM is based on an effective Lagrangian, where baryons are described by relativistic valence quarks and a perturbative cloud of Goldstone bosons as required by chiral symmetry. We discuss for example applications to electromagnetic properties of the octet baryons and σ‐term physics. Furthermore, we present recent efforts to formulate and apply a manifestly Lorentz covariant chiral quark model, which is consistent with the latest developments in the baryon sector of chiral perturbation theory.

Nucleon-Nucleon High-Energy Scattering

The high energy pn charge exchange and pp elastic scattering reactions are studied in an effective hadron model for the energy range of s ~ 50 to 400 GeV2. The main features of the observed differential cross section of the pn charge exchange reaction, the forward peak and the scaling behavior over the large energy range, are well reproduced by a combination of π-, ρ-exchange and a 4-Nucleon contact term. The latter acts as a background field which turns out to be naturally suppressed in elastic N N scattering but contributes significantly to the charge-exchange reaction.

Chiral dynamics of baryons in a covariant quark model

Abstract We developed a manifestly Lorentz covariant chiral quark model for the study of baryons as bound states of constituent quarks in an extension of our previous approach. The investigations are related to the ongoing and planned experiments on improved measurements of the elastic baryon form factors and their decay characteristics. The approach is based on a non-linear chirally symmetric Lagrangian, which involves effective degrees of freedom—constituent quarks and the chiral (meson) fields. In a first step, this Lagrangian can be used to perform a dressing of the constituent quarks by a cloud of light pseudoscalar mesons and other heavy states using the calculational technique developed by Becher and Leutwyler. We calculate the dressed transition operators with a proper chiral expansion which are relevant for the interaction of quarks with external fields in the presence of a virtual meson cloud. These operators are used in the calculation of baryon matrix elements.