Importance of loop effects in probing lepton number violation

The discovery of the lepton number violation would be a smoking gun signal for physics beyond the Standard Model, and its most sensitive probe is the search for neutrinoless double beta decay ( 0 ν β β ). Working in the framework of the Standard Model effective field theory (SMEFT), we show that one-loop effects can remarkably improve the tree-level bounds on the new physics scales for several dimension-7 operators. Using ultraviolet model examples, we then showcase the competition among 0 ν β β contributions induced by dimension-7 and loop-level dimension-5 SMEFT operators.