Speaker
Description
A popular choice for a new mediator between the Standard Model (SM) and a dark sector are kinetically mixed hidden photons. However, beyond a minimal kinetic mixing coupling such a new vector boson can also have gauge interactions with SM particles. In general, these gauge interactions are constrained by anomaly cancellation, fermion mass terms and the CKM and PMNS matrix. In this talk I will demonstrate that these constraints only allow for a limited number of Abelian gauge extensions of the SM without the introduction of new chiral fermions. I will furthermore argue that of these gauge groups only $U(1)_{B-L}$ can allow for Dirac neutrino masses, while for all other choices neutrinos must have Majorana masses. For this whole class of new vector bosons there is ample parameter space with rich forward physics phenomenology. I will show that FASER and FASER$\nu$ as representative forward physics experiments will play a crucial role in the future search for these bosons.
