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Abstract |
The reach of ab initio calculations has extended significantly over the past years. In
particular systems revealing a closed-shell character can be described efficiently up to
the tin isotopic chain via controlled many-body expansions like coupled-cluster the-
ory, the in-medium similarity renormalization group or self-consistent Green func-
tion techniques. However, the transfer of such methods to open-shell nuclei requires
a highly non-trivial extension. In this talk we will discuss many-body perturbation
theory (MBPT) as a light-weighted alternative and give a pedestrian introduction to
MBPT based on a Hartree-Fock reference state. Low-order energy corrections for
ground states of closed-shell nuclei will be discussed using state-of-the-art chiral
interactions.
The conceptual simplicity of MBPT allows for a direct generalization to open-shell
systems by using correlated reference states. First I will present a MBPT version us-
ing a multi-configurational reference state arising from a prior no-core shell-model
calculation (NCSM). We present recent calculations of second-order energy correc-
tions of spectra of even and odd carbon and oxygen isotopes and compare them to
exact diagonalizations from large-scale NCSM calculations. Additionally, we will
provide first results on the dripline physics of the fluorine isotopic chain.
In a complementary ansatz we use symmetry-broken reference states from a Hartree-
Fock-Bogoliubov (HFB) calculation as starting point for the correlation expansion
and reformulate MBPT in a quasiparticle setting yielding the so-called Bogoliubov
MBPT (BMBPT). We present preliminary results for the oxygen chain and compare
them to other state-of-the-art many-body approaches and provide an outlook on
future applications of symmetry-broken many-body approaches. |
