Hypernuclear single particle spectra based on in-medium chiral SU(3) dynamics

Abstract

A previously derived relativistic energy density functional for nuclei, based on low-energy in-medium chiral dynamics, is generalized to implement constraints from chiral SU(3) effective field theory and applied to $\Lambda$ hypernuclei. Density-dependent central and spin-orbit mean fields are calculated for a $\Lambda$ hyperon using the SU(3) extension of in-medium chiral perturbation theory to two-loop order. Long range $\Lambda N$ interactions arise from kaon-exchange and from two-pion-exchange with a $\Sigma$ hyperon in the intermediate state. Short-distance dynamics is encoded in contact interactions. They include scalar and vector mean fields reflecting in-medium changes of quark condensates, constrained by QCD sum rules. The $\Lambda$ single particle orbitals are computed for a series of hypernuclei from ${}_{\Lambda }^{13}$C to ${}_{\Lambda }^{208}$Pb. The role of a surface (derivative) term is studied. Its strength is found to be compatible with a corresponding estimate from in-medium chiral perturbation theory. Very good agreement with hypernuclear spectroscopic data is achieved. The smallness of the $\Lambda$-nuclear spin-orbit interaction finds a natural explanation in terms of an almost complete cancellation between short-range scalar/vector contributions and longer range terms generated by two-pion exchange.

Comments: 30 pages, 5 figures, elsart class, minor corrections, to be published in Nuclear Physics A