Collider imprints of a right handed neutrino magnetic moment operator

We consider the most general effective Lagrangian up to dimension five, built with Standard Model fields and right-handed neutrinos (RHNs) $N_i$. Assuming that the RHNs are present near the electroweak scale, we study the phenomenology of the RHNs and highlight the differences that arise due to the inclusion of dimension five operators. We specifically focus on the production process $e^{+}{e}^{-}/pp\to N_i{N}_j$, which comes from the dimension five magnetic moment operator. We find that this production process followed by the decay chains such as $N_i\to N_j\gamma$, $N_i\to {\nu }_j\gamma$, and $N_i\to {\ell }^{\pm }jj$ leads to striking collider signatures, which might help to probe the Majorana nature of neutrinos. We discuss the current collider constraints on this operator, as well as projected limit at future colliders. In addition, we discuss the stellar-cooling bounds applicable to the RHN mass below 0.1 GeV.