Eur. Phys. J. A (2013) 49: 39
https://doi.org/10.1140/epja/i2013-13039-2

Letter

Chiral three-nucleon forces and bound excited states in neutron-rich oxygen isotopes

¹³⁹ Department of Physics and Astronomy, University of Tennessee, 37996, Knoxville, TN, USA
²³⁹ Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, 37831, Oak Ridge, TN, USA
³³⁹ Institut für Kernphysik, Technische Universität Darmstadt, 64289, Darmstadt, Germany
⁴³⁹ ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany

^* e-mail: schwenk@physik.tu-darmstadt.de

Received: 11 February 2013
Accepted: 12 February 2013
Published online: 22 March 2013

Abstract

We study the spectra of neutron-rich oxygen isotopes based on chiral two- and three-nucleon interactions. First, we benchmark our many-body approach by comparing ground-state energies to coupled-cluster results for the same two-nucleon interaction, with overall good agreement. We then calculate bound excited states in ^{21, 22, 23}O , focusing on the role of three-nucleon forces, in the standard sd shell and an extended valence space. Chiral three-nucleon forces provide important one- and two-body contributions between valence neutrons. We find that both these contributions and an extended valence space are necessary to reproduce key signatures of novel shell evolution, such as the N = 14 magic number and the low-lying states in ²¹O and ²³O , which are too compressed with two-nucleon interactions only. For the extended space calculations, this presents first work based on nuclear forces without adjustments. Future work is needed and open questions are discussed.