How dark is the ${\nu }_R$-philic dark photon?

Abstract

We consider a generic dark photon that arises from a hidden $U(1)$ gauge symmetry imposed on right-handed neutrinos (${\nu }_R$). Such a ${\nu }_R$-philic dark photon is naturally dark due to the absence of tree-level couplings to normal matter. However, loop-induced couplings to charged leptons and quarks are inevitable, provided that ${\nu }_R$ mix with left-handed neutrinos via Dirac mass terms. We investigate the loop-induced couplings and find that the ${\nu }_R$-philic dark photon is not inaccessibly dark, which could be of potential importance to future dark photon searches at SHiP, FASER, Belle-II, LHC 14 TeV, etc.

Comments: 22 pages, 3 figures, 1 table, FASER bound updated, JHEP published version