Abstract
We introduce a dark neutrino sector which respects a hidden $U(1)^\prime$ gauge symmetry, subsequently broken by the vacuum expectation value of a dark scalar. The model is a self-consistent realisation of an extended hidden sector that communicates with the SM only via the three renormalizable portals, namely neutrino, vector and scalar mixing. The interplay between portal couplings leads to several novel signatures in heavy neutrino, dark photon, and dark scalar searches, typically characterised by multi-leptons plus missing energy and displaced vertices. A striking signature arises in kaon factories such as NA62, where $K^+\to\ell_\alpha^+\nu \ell_\beta^+\ell_\beta^-$ decays could reveal a heavy neutrino and a light dark photon resonance above backgrounds. Given the open parameter space, we also comment on recent ideas to explain outstanding experimental anomalies, and how they would fit in our proposed model. A minimal extension of the model, possibly motivated by anomaly cancellation, can accommodate a dark matter candidate strongly connected to the neutrino sector.
Highlights
The most important evidence that the standard model (SM) of particle physics is incomplete comprises neutrino masses and mixing, and the presence of dark matter (DM) in the Universe
We have proposed a new model which invokes the existence of a hidden Uð1Þ0 symmetry confined to a new dark neutrino sector
Without restricting to the region where our model generates the correct neutrino masses, we explored a series of experimental signatures that may arise from the interplay of portal couplings
Summary
The most important evidence that the standard model (SM) of particle physics is incomplete comprises neutrino masses and mixing, and the presence of dark matter (DM) in the Universe. The broken gauge symmetry implies the existence of a light hidden gauge boson Xμ, which mediates the dark neutrino interactions and generically kinetically mixes with the SM hypercharge This self-consistent setup combines the three portals into a unified picture that exhibits significantly different phenomenology with respect to each portal taken separately. An interesting feature of the model is the generation of neutrino masses at loop level This requires only two key features of our setup, namely, a light Z0 and neutrino mixing, but not the vector and scalar portals. In its minimal form, the model is not anomaly free We discuss how this can be cured and propose a minor extension that introduces additional dark sector neutral fermions charged under the new symmetry [1,2]. We briefly outline the key features of a DM extension and leave a more detailed analysis to future work
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