Tree-level UV completions for $N_R$SMEFT $d=6$ and $d=7$ operators

Abstract

We study ultra-violet completions for operators in standard model effective field theory extended with right-handed neutrinos ($N_R$SMEFT). Using a diagrammatic method, we generate systematically lists of possible tree-level completions involving scalars, fermions or vectors for all operators at $d=6$ and $d=7$, which contain at least one right-handed neutrino. We compare our lists of possible UV models to the ones found for pure SMEFT. We also discuss how the observation of LNV processes via $N_R$SMEFT operators at the LHC can be related to Majorana neutrino masses of the standard model neutrinos.