Speaker
Description
The invisible decay of cold dark matter into a slightly lighter dark sector particle on cosmological time-scales has been proposed as a solution to the $S_8$ tension. In this talk, I want to present a possible embedding of this scenario within a particle physics framework and discuss its phenomenology. The model is set up of a minimal dark matter decay, where the dark sector contains two singlet fermions $N_{1,2}$, quasi-degenerate in mass, and carrying lepton number so that the heaviest state ($N_2$) decays into the lightest ($N_1$) and two neutrinos via a higher-dimensional operator $N_2 \to N_1\nu\nu$. Due to the present symmetries and small phase space, the decays into photons or charged leptons are strongly suppressed and thus its stringent constraints from indirect dark matter searches can be avoided. Additionally, complementary constraints on the model parameters arise from neutrino detectors, freeze-in dark matter production, collider experiments and blazar observations. Together, these single out dark matter masses below $\sim1$ GeV where constraints still allow for model parameters addressing the $S_8$ tension. Signals of dark matter in this parameter space of interest could be detected by the upcoming JUNO neutrino observatory.
