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HK: Physik der Hadronen und Kerne
HK 9: Poster Session: Theory
HK 9.13: Poster
Tuesday, March 12, 2002, 10:30–12:45, Foyer Chemie
Nuclear spin-orbit interaction from chiral pion-nucleon dynamics — •Norbert Kaiser — Physik-Department T39, TU-München, 85747 Garching
Using the two-loop approximation of chiral perturbation theory, we calculate the momentum and density dependent nuclear spin-orbit strength Uls(p,kf). This quantity is derived from the spin-dependent part of the interaction energy Σspin = i/2 σ→· (q→ ×p→ ) Uls(p,kf) of a nucleon scattering off weakly inhomogeneous isospin symmetric nuclear matter from initial momentum p→−q→/2 to final momentum p→+q→/2. We find that iterated 1π-exchange generates at saturation density kf0=272.7 MeV a spin-orbit strength at p=0 of Uls(0,kf0)= 35.1 MeVfm2 in perfect agreement with the empirical value used in the shell model. This novel spin-orbit strength is neither of relativistic nor of short range origin. In fact it is linearly proportional to the nucleon mass M and its range is the pion Compton wave length mπ−1 =1.46 fm. The potential Vls underlying the spin-orbit strength Uls= Vls rls2 becomes a rather weak one, Vls=17 MeV, after the identification rls=mπ−1 as suggested by the present calculation. We observe however a strong p-dependence of Uls(p,kf0) leading even to a sign change at p=200 MeV. This and other features of Σspin which go beyond the usual shell model parametrization leave questions concerning the ultimate relevance of the spin-orbit interaction generated by 2π-exchange in a finite nucleus. We calculate also the isovector part of the single particle potential in isospin asymmetric nuclear matter proportional to τ3 (N−Z)/(N+Z) and find reasonable agreement with empirical values.
Work supported in part by BMBF, DFG and GSI.