arXiv subjects

G. Krein

Publications and source records attributed to G. Krein.

113 records · Page 7Linked to original sources

arXiv1995

Studying medium effects with the optimized $\bdelta$ expansion

The possibility of using the optimized $δ$ expansion for studying medium effects on hadronic properties in quark or nuclear matter is investigated. The $δ$ expansion is employed to study density effects with two commonly used models in hadron and nuclear physics, the Nambu--Jona-Lasinio model for the dynamical chiral symmetry breaking and the Walecka model for the equation of state of nuclear matter. The results obtained with the $δ$ expansion are compared to those obtained with the traditional Hartree-Fock approximation. Perspectives for using the $δ$ expansion in other field theoretic models in hadron and nuclear physics are discussed.

hep-ph↗

arXiv1993

Self-consistent solution of the Schwinger-Dyson equations for the nucleon and meson propagators

The Schwinger-Dyson equations for the nucleon and meson propagators are solved self-consistently in an approximation that goes beyond the Hartree-Fock approximation. The traditional approach consists in solving the nucleon Schwinger-Dyson equation with bare meson propagators and bare meson-nucleon vertices; the corrections to the meson propagators are calculated using the bare nucleon propagator and bare nucleon-meson vertices. It is known that such an approximation scheme produces the appearance of ghost poles in the propagators. In this paper the coupled system of Schwinger-Dyson equations for the nucleon and the meson propagators are solved self-consistently including vertex corrections. The interplay of self-consistency and vertex corrections on the ghosts problem is investigated. It is found that the self-consistency does not affect significantly the spectral properties of the propagators. In particular, it does not affect the appearance of the ghost poles in the propagators.

nucl-th↗

arXiv1993

Charge-Symmetry Breaking, Rho-Omega Mixing and the Quark Propagator

The momentum-dependence of the $ρ^0$-$ω$ mixing contribution to charge-symmetry breaking (CSB) in the nucleon-nucleon interaction is compared in a variety of models. We focus in particular on the role that the structure of the quark propagator plays in the predicted behaviour of the $ρ^0$-$ω$ mixing amplitude. We present new results for a confining (entire) quark propagator and for typical propagators arising from explicit numerical solutions of quark Dyson-Schwinger equations. We compare these to hadronic and free quark calculations. The implications for our current understanding of CSB experiments is discussed.

nucl-th↗

arXiv1993

The Off Shell $ρ$-$ω$ Mixing in the QCD Sum Rules

The $q^2$ dependence of the $ρ-ω$ mixing amplitude is analyzed with the use of the QCD sum rules and the dispersion relation. Going off shell the mixing decreases, changes sign at $q^2 \simeq 0.4 m_ρ^2 > 0$ and is negative in the space like region. Implications of this result to the isospin breaking part of the nuclear force are discussed.

nucl-th↗

arXiv1993

Ghost Poles in the Nucleon Propagator: Vertex Corrections and Form Factors

Vertex corrections are taken into account in the Schwinger-Dyson equation for the nucleon propagator in a relativistic field theory of fermions and mesons. The usual Hartree-Fock approximation for the nucleon propagator is known to produce the appearance of complex (ghost) poles which violate basic theorems of quantum field theory. In a theory with vector mesons there are vertex corrections that produce a strongly damped vertex function in the ultraviolet. One set of such corrections is known as the Sudakov form factor in quantum electrodynamics. When the Sudakov form factor generated by massive neutral vector mesons is included in the Hartree-Fock approximation to the Schwinger-Dyson equation for the nucleon propagator, the ghost poles disappear and consistency with basic requirements of quantum field theory is recovered.

nucl-th↗