Speaker
Description
The observation of lepton number violation (LNV) would be clear evidence for physics beyond the Standard Model, and non-zero neutrino masses particularly motivate a study of processes that violate lepton number by two units, like e.g. neutrinoless double beta decay.
In the Standard Model Effective Field Theory (SMEFT), $\Delta L =2$ operators appear at dimension-5 and higher odd dimensions.
Focusing on dimension-9 operators, I will present a diagram-based classification of tree-level UV models and isolate minimal two-particle models that avoid generating the dimension-5 operator or dimension-7 LNV operators at tree level.
I then chart how these minimal models populate the operator landscape and organise them by the loop order at which they radiatively induce lower-dimensional LNV operators, highlighting scenarios in which the tree-level dimension-9 contribution can compete with or dominate loop-suppressed neutrino-mass (dimension-5) effects.
For a representative model, I will show the matching onto the SMEFT, its implications for neutrino masses and the relative size of dimension-9 versus dimension-5 contributions to neutrinoless double beta decay.