Uncovering a chirally suppressed mechanism of $0νββ$ decay with LHC searches

Michael L. Graesser, Gang Li, Michael J. Ramsey-Musolf, Tianyang Shen, Sebastián Urrutia-Quiroga

Published 2022-02-02Version 1

$\Delta L =2$ lepton number violation (LNV) at the TeV scale could provide an alternative interpretation of positive signal(s) in future neutrinoless double beta $(0\nu\beta\beta)$ decay experiments. An interesting class of models from this point of view are those that at low energies give rise to dimension-9 vector operators and a dimension-7 operator, both of whose $0\nu\beta\beta$-decay rates are "chirally suppressed". We study and compare for the first time the sensitivities of $0\nu\beta\beta$-decay experiments and LHC searches to a simplified model in this class of TeV-scale LNV. Due to the chiral suppression of the vector operators, $0\nu\beta\beta$-decay searches are found to be less constraining than LHC searches. For the chirally suppressed dimension-7 operator generated by TeV-scale mediators, in contrast, $0\nu\beta\beta$-decay searches place strong constraints on the size of the new Yukawa coupling. Signals of this model at the LHC and $0\nu\beta\beta$-decay experiments are entirely uncorrelated with the observed neutrinos masses, as these new sources of LNV give negligible contributions to the latter. We find the prospects for the high-luminosity LHC and ton-scale $0\nu\beta\beta$-decay experiments to uncover the chirally-suppressed mechanism with TeV-scale LNV to be promising. We also comment on the sensitivity of the $0\nu\beta\beta$-decay lifetime to certain unknown low-energy constants that in the case of dimension-9 {\it scalar} operators are expected to be large due to non-perturbative renormalization.