Berlin 2005 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 34: Theorie
HK 34.7: Vortrag
Dienstag, 8. März 2005, 18:00–18:15, TU MA042
Chiral SU(3) dynamics, QCD sum rules and Λ-hyperons in the nuclear medium — •Norbert Kaiser, Bernhard Langwallner, and Wolfram Weise — Physik-Department, TU München, D-85747 Garching, Germany
We present a novel approach to the density dependent mean field and the spin-orbit interaction of a Λ-hyperon in nuclear many-body systems, based on flavor-SU(3) in-medium chiral perturbation theory. The leading long-range Λ N-interaction arises from kaon exchange and from two-pion exchange with a Σ-hyperon in the intermediate state. The empirical Λ-nucleus potential depth of about −28 MeV is well reproduced with a single cutoff scale, Λ= 0.7 GeV, effectively representing all short-distance (high-momentum) dynamics not resolved at scales characteristic of the nuclear Fermi momentum. The smallness of the Λ-nuclear spin-orbit interaction finds a natural (yet novel) explanation in terms of an almost complete cancellation between short-range contributions (properly rescaled from the known nucleonic spin-orbit coupling strength) and long-range terms generated by iterated one-pion exchange with intermediate Σ-hyperons. The small ΣΛ-mass difference figures prominently in this context. We perfom a similar calculation for the complex-valued Σ-nuclear mean field UΣ(kf) + i WΣ(kf). At saturation density two-pion exchange with Λ-hyperons in the intermediate state gives rise to an imaginary part of WΣ(kf0)= −21.5 MeV in good agreement with the value extracted from the width of Σ− atom states. We also examine connections with in-medium QCD sum rules for hyperons.