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 ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mn>0</a:mn> <a:mi>ν</a:mi> <a:mi>β</a:mi> <a:mi>β</a:mi> </a:math> ). 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 <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mn>0</c:mn> <c:mi>ν</c:mi> <c:mi>β</c:mi> <c:mi>β</c:mi> </c:math> contributions induced by dimension-7 and loop-level dimension-5 SMEFT operators.