Fabian Esser: Higher-dimensional SMEFT operators and UV models for neutrinoless double beta decay

Thursday 12 Mar 2026, 11:00 → 12:00 Europe/Ljubljana

A/1-106 - Seminarska soba fizike (F5)

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), a ubiquitous framework used for indirect new physics searches, $\Delta L =2$ 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 sce- narios in which the tree-level dimension-9 contribution can compete with or dominate loop-suppressed neutrino-mass (dimension-5) effects. Finally, I will show representative one-loop and two- loop models, their matching onto the SMEFT, and their implications for neutrino masses, charged-lepton flavour violation, and the relative size of dimension-9 versus dimension-5 contributions to 0νββ.