Speaker
Description
We examine the prospect of probing extensions of the Standard Model (SM) involving heavy neutral leptons (HNLs) at FCC-ee. Using the effective field theory (EFT) approach, we determine the impact of new interactions on the production and decay of HNLs at FCC-ee. In particular, we consider EFT operators which induce vector, scalar and tensor four-fermion interactions and effective charged- and neutral-current interactions of HNLs, which may also mix with the active neutrinos of the SM. We first consider constraints on the active-sterile mixing and EFT Wilson coefficients from monophoton searches. We then investigate the constraints from displaced vertex decay signatures. In both analyses, we consider the scenarios where the HNLs are Dirac or Majorana fermions.