Köln 2004 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 5: Theory I
HK 5.4: Vortrag
Montag, 8. März 2004, 16:45–17:00, D
Three-body spin-orbit forces from chiral two-pion exchange — •Norbert Kaiser — Physik Department T39, Technische Universität München, D-85747 Garching, Germany
Using chiral perturbation theory, we calculate the density-dependent
spin-orbit
coupling generated by the two-pion exchange three-nucleon interaction
involving
virtual Δ-isobar excitation. From the corresponding three-loop
Hartree
and Fock diagrams we obtain an isoscalar spin-orbit strength Fso(kf)
which amounts at nuclear matter saturation density to about half of the
empirical value of 90 MeVfm5. The associated isovector spin-orbit
strength Gso(kf) comes out about a factor of 20 smaller.
Interestingly, this three-body spin-orbit coupling is not a relativistic
effect
but independent of the nucleon mass M. Furthermore, we calculate the
three-body spin-orbit coupling generated by two-pion exchange on the
basis of the most general chiral ππ NN-contact interaction. We find
similar (numerical) results for the isoscalar and isovector spin-orbit
strengths Fso(kf) and Gso(kf) with a strong dominance
of
the p-wave part of the ππ NN-contact interaction and the Hartree
contribution. We consider also the effect of iterated pion-photon exchange
on
the Coulomb energy of nuclei. It leads to an additional binding of each
proton
by about 0.2 MeV. We propose as a mechanism to resolve the
Nolen-Schiffer anomaly the iteration of one-photon exchange with a
short-range pp-interaction. The corresponding energy per proton reads:
Ē[ρp]= (2/15π2)(π2 −3+6 ln2) App kp2 with ρp
=kp3/3π2 the proton density.
N. Kaiser, Phys. Rev. C68 (2003) 054001.
Work supported in part by BMBF, GSI and DFG.