Angular-momentum projection in coupled-cluster theory: structure of ³⁴Mg

Single-reference coupled-cluster theory is an accurate and affordable computational method for the nuclear many-body problem. For open-shell nuclei, the reference state typically breaks rotational invariance and angular momentum must be restored as a good quantum number. We employ the disentangled coupled-cluster formalism and a Hermitian approach for the angular momentum projection.  Our results agree with benchmarks and data for ⁸Be and ²⁰Ne using a two-nucleon interaction from chiral effective field theory and for pf-shell nuclei within a traditional shell model. We predict the rotational band in the exotic nucleus ³⁴Mg.