arXiv subjects
Publications and source records attributed to T. Waas.
Models based on chiral SU(3)_L \otimes SU(3)_R symmetry and vector meson dominance suggest an attractive potential for the $ω$-meson in a nuclear medium. We discuss the feasibility of producing nuclear bound states of $ω$-mesons using $(d,^3He)$ and pion induced reactions on selected nuclear targets.
The vacuum spectrum of the $ϕ$-meson is characterized by its decay into $K{\bar K} $. Modifications of the $K {\bar K}$-loops in baryonic matter change this spectrum. We calculate these in-medium modifications taking both s- and p-wave kaon-nucleon interactions into account. We use results of the in-medium $K$ and $\bar K$ spectra determined previously from a coupled channel approach based on a chiral effective Lagrangian. Altogether we find a very small shift of the $ϕ$ meson mass, by less than 10 MeV at normal nuclear matter density $ρ_0$. The in-medium decay width of the $ϕ$ meson increases such that its life time at $ρ=ρ_0$ is reduced to less than 5 fm/c. It should therefore be possible to observe medium effects in reactions such as $π^- p \to ϕn$ in heavy nuclei, where the $ϕ$ meson can be produced with small momentum.
We show that the s-wave pion-nuclear potential which reproduces the deeply bound pionic states in Pb, recently discovered at GSI, is remarkably close to the one constructed directly from low energy theorems based on chiral symmetry. Converting this information into an effective pion mass we find $m_π^\star/m_π\simeq 1.13$ in the center of the Pb nucleus, and $m_π^\star/m_π\simeq 1.07$ in symmetric nuclear matter.
We evaluate the effective kaon mass in dense nuclear matter. Pauli blocking and nucleon-nucleon short-range correlations are incorporated. The effects of short-range correlations are shown to be moderate and figure importantly only at densities larger than 2 times normal nuclear density. We discuss the relations between the present results and the results obtained in next-to-next-to-leading order chiral perturbation theory (${{\cal O} (Q^3)}$, where $Q$ is the characteristic small energy-momentum scale probed). We also discuss mean-field aspects, with some remarks on the relation between the short-range correlations and the four-Fermi contact terms in the chiral effective Lagrangian.
We identify the leading s-wave amplitudes of the SU(3) chiral meson-baryon Lagrangian with an effective coupled-channel potential which is iterated in a Lippmann-Schwinger equation. The strangeness $S=-1$ resonance $Λ(1405)$ and the $S_{11}(1535)$ nucleon resonance emerge as quasi-bound states of anti-kaon/nucleon and kaon/$Σ$-hyperon. Our approach to meson photoproduction introduces no new parameters. By adjusting a few finite range parameters we are able to simultaneously describe a large amount of low energy data. These include the cross sections of $K^-p$ elastic and inelastic scattering, the cross sections of eta meson and kaon photoproduction from nucleons as well as those of pion induced production of etas and kaons (16 different reaction channels altogether).