Ab initio Description of Neutrinoless Double Beta Decay with the In-Medium Similarity Renormalization Group*

Recently, there has been significant progress in ab initio calculations 

of the nuclear matrix elements (NMEs) for neutrinoless double beta decay (NLDBD).

Methods like the In-Medium Similarity Renormalization Group (IMSRG) and

Coupled Cluster Theory have produced first results for candidate 

nuclei based on interactions from chiral effective field theory [1,2,3], and 

efforts are underway towards improved consistency and uncertainties.

In this context, Cirigliano et al. have pointed out the presence of a 

leading-order counter term in the EFT-based NLDBD transition operator,

and proposed a protocol for determining its coupling [4]. We have 

implemented this counter term and studied its impact in benchmark calculations 

for light nuclei as well as the lightest realistic NLDBD candidate, 48Ca. Encouragingly, 

we obtain a robust enhancement of the NMEs, although we stress

that fully consistent results are still pending.

[1] J. M. Yao et al., PRL 124, 232501

[2] A. Belley et al., PRL 126, 042502

[3] S. J. Novario et al., PRL 126, 182502

[4] V. Cirigliano et al., PRL 126, 172002