Matthias F. M. Lutz

Nuclear kaon dynamics

Abstract An effective low energy Lagrangian density is applied to nuclear K − -dynamics. The free parameters, local s-wave couplings and SU (3)-symmetry constrained range terms are adjusted to describe elastic and inelastic K − -nucleon scattering data. The propagation and decay of the Λ (1405)-resonance and the Λ (1405)-nucleon hole state is studied self consistently with respect to the K − -propagation in isospin symmetric nuclear matter.

Meson properties at finite temperature and baryon density

Abstract We use the generalized SU(3) version of the Nambu and Jona-Lasinio model to discuss properties of mesons, constituent quarks and vacuum structure as a function of density and temperature in compressed matter. Systematic low-density expansions are derived. In particular, we show that effects due to finite quasi-particle size are important in stabilizing the density and temperature dependence of the pion mass.

Generalized SU(3) {Nambu-Jona-Lasinio} Model. Part 2. From Current to Constituent Quarks

Abstract We investigate the properties of constituent quarks, i.e. quarks dressed by their strong interactions, in a generalized Nambu-Jona-Lasinio model with Nf = 3 flavours. In the Hartree-Fock approximation, the step from structureless current quarks to massive constituent quarks is made through dynamical mass generation which implies spontaneous chiral symmetry breaking. We study, in particular, the quark scalar, vector and axial vector currents within this framework. We demonstrate that, at low energy and momentum transfers, single valence quarks are strongly screened by quark-antiquark polarization effects. For the electromagnetic currents, we recover relationships familiar from the vector meson dominance model. For the axial current, screening by Jπ = 1+ quark-antiquark modes leads to an effective quark axial vector constant gA

Chiral phase transition in the SU(3) Nambu and Jona-Lasinio model

Abstract We calculate the thermodynamical potential of the SU(3) Nambu and Jona-Lasinio model in the mean field approximation and discuss the nature of the chiral phase transition. i.e. the mechanisms which govern chiral symmetry restoration at large temperature and/or quark densities. No evidence is found for a first order transition once realistic coupling strengths are used in the model.

Kaons in baryonic matter

Abstract We investigate modifications of the kaon mass in baryonic matter. It is rigorously established that at small density the in-medium kaon masses are determined by the kaon-nucleon scattering amplitude. Using empirical numbers there is no tendency towards s-wave K + condensation. We explore and discuss consequences of chiral symmetry for kaon-nuclear systems.

Radiative and isospin-violating decays of Ds-mesons in the hadrogenesis conjecture

Abstract The masses and decays of the scalar D s 0 ∗ (2317) and axial-vector D s 1 ∗ ( 2460 ) charmed strange mesons are calculated consistently in the hadrogenesis conjecture. These mesons decay either strongly into the isospin-violating π 0 D s and π 0 D s ∗ channels or electromagnetically. They are generated by coupled-channel dynamics based on the leading order chiral Lagrangian. The effect of chiral corrections to chiral order Q χ 2 is investigated. We show that taking into account large- N c relations to determine the strength of these correction terms implies a measurable signal for an exotic axial-vector state in the η D ∗ invariant mass distribution. The one-loop contribution to the electromagnetic decay amplitudes of scalar and axial-vector states is calculated. The Lagrangian describing electromagnetic interactions is obtained by gauging the chiral Lagrangian for hadronic interactions and adding gauge-invariant correction terms to chiral order Q χ 2 . In addition the role of light vector meson degrees of freedom is explored. We confront our results with measured branching ratios. Once the light vector mesons are included, a natural explanation of all radiative decay parameters is achieved.

Effective chiral theory of nucleon–nucleon scattering

Abstract We present a new chiral expansion scheme for the nucleon–nucleon scattering amplitude which preserves unitarity exactly. Our effective field theory builds on the power counting rules for 2-nucleon reducible diagrams. We evaluate the leading order terms of the isospin one scattering amplitude and elaborate in detail on the 1 S 0 phase shift. Our chiral description of the 1 S 0 -phase shift does compete in quality with modern phenomenological nucleon–nucleon potentials. We describe elastic and inelastic scattering quantitatively up to laboratory energies of E lab ≃600 MeV.

Kaons and strange quarks in dense matter

Abstract We study the change of the masses and decay constants of K + and K − mesons in a dense nuclear medium, using the framework of the SU (3) Nambu and Jona-Lasinio model. We do not observe a tendency towards kaon condensation in this model.

Sizes of hadrons

Abstract We summarize and discuss recent developments in the analysis and interpretation of hadronic radii. The Nambu and Jona-Lasinio model is used to describe the dynamical step from pointlike current quarks to constituent quarks with finite sizes. We show how the “dressing” of quarks with quark-antiquark polarization clouds contributes to hadronic sizes and clarify the connection with the vector meson dominance model.

Nc-counting rules and the axial vector coupling constant of the constituent quark.

We analyze the axial vector coupling of the constituent quark in the large-[ital N][sub [ital c]] limit and point out mechanisms which yield 1[minus][ital g][sub [ital A]][similar to][ital N][sub [ital c]][sup 0].