A quark model framework for the study of nuclear medium effects

Abstract

A quark-model framework for studying nuclear medium effects on nucleon resonances is described and applied here to pion photoproduction on the deuteron, which is the simplest composite nucleon system and serves as a first test case. Pion photoproduction on nuclei is discussed within a chiral constituent quark model in which the quark degrees of freedom are explicitly introduced through an effective chiral Lagrangian for the quark-pseudoscalar-meson coupling. The advantage of this model is that a complete set of nucleon resonances can be systematically included with a limited number of parameters. Also, the systematic description of the nucleon and its resonances at quark level allows us to self-consistently relate the nuclear medium's influence on the baryon properties to the intrinsic dynamic aspects of the baryons. As the simplest composite nucleus, the deuteron represents the first application of this effective theory for meson photoproduction on light nuclei. The influence of the medium on the transition operators for a free nucleon is investigated in the Delta resonance region. No evidence is found for a change of the Delta properties in the pion photoproduction reaction on the deuteron since the nuclear medium here involves just one other nucleon and the low binding energy implies low nuclear density. However, we show that the reaction mechanism is in principle sensitive to changes of Delta properties that would be produced by the denser nuclear medium of heavier nuclei through the modification of the quark model parameters.

Highly efficient and exact method for parallelization of grid‐based algorithms and its implementation in DelPhi

“…The APBS is a popular multigrid finite difference and adaptive finite element PBES developed by Dr. N. Baker and his colleagues and is aimed at providing force estimates and modeling large biomolecules and assemblages and pKa cal-culations. Another popular poisson boltzmann (PB) solver is MIBPB, [12,13,[19][20][21][22] developed by Wei and coworkers which uses interface technique to assure potential and flux continuity at the interface biomolecule and solvent. Because of this and Krylov subspace technique [12,[19][20][21][22] implementation, the MIBPB was demonstrated to be very robust PBES achieving second-order convergence for solving linear PBE.…”

“…Another popular poisson boltzmann (PB) solver is MIBPB, [12,13,[19][20][21][22] developed by Wei and coworkers which uses interface technique to assure potential and flux continuity at the interface biomolecule and solvent. Because of this and Krylov subspace technique [12,[19][20][21][22] implementation, the MIBPB was demonstrated to be very robust PBES achieving second-order convergence for solving linear PBE. [13] The third popular solver is DelPhi, developed in Honig and coworkers laboratory, [1,18] which adopts the Gauss-Seidel (GS) method, combined with the successive over-relaxation (SOR) method which estimates the best relaxation parameter at run time [23] to solve both linear and nonlinear PBES.…”