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arXiv · 1807.11053

Generator-coordinate reference states for spectra and $0νββ$ decay in the in-medium similarity renormalization group

J. M. Yao·J. Engel·L. J. Wang·C. F. Jiao·H. Hergert
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Abstract

We use a reference state based on symmetry-restored states from deformed mean-field or generator-coordinate-method (GCM) calculations in conjunction with the in-medium similarity-renormalization group (IMSRG) to compute spectra and matrix elements for neutrinoless double-beta ($0νββ$) decay. Because the decay involves ground states from two nuclei, we use evolved operators from the IMSRG in one nucleus in a subsequent GCM calculation in the other. We benchmark the resulting IMSRG+GCM method against complete shell-model diagonalization for both the energies of low-lying states in $^{48}$Ca and $^{48}$Ti and the $0νββ$ matrix element for the decay of $^{48}$Ca, all in a single valence shell. Our approach produces better spectra than either the IMSRG with a spherical-mean-field reference or GCM calculations with unevolved operators. For the $0νββ$ matrix element the improvement is slight, but we expect more significant effects in full ab-initio calculations.

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J. M. Yao, J. Engel, L. J. Wang, C. F. Jiao, H. Hergert. 2018-11-05. Generator-coordinate reference states for spectra and $0νββ$ decay in the in-medium similarity renormalization group. https://doi.org/10.1103/physrevc.98.054311

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