  Light dark matter (DM) in the GeV ballpark faces weaker constraint from
direct detection experiments. If such DM also has sufficient self-interactions
due to a light mediator, it can alleviate the small-scale problems of the cold
dark matter (CDM) paradigm while being consistent with the latter at large
scales, as suggested by astrophysical observations. However, generating correct
thermal relic for such light DM is challenging. While GeV scale CDM typically
leads to thermal overproduction due to the absence of sufficient annihilation
channels, self-interacting dark matter (SIDM) typically has under-abundant
thermal relic due to its large annihilation rates into mediator particles. In
this letter, we propose a minimal realisation of GeV scale SIDM with correct
thermal relic, where one of the three singlet fermions, responsible for seesaw
origin of light neutrino masses, assists in generating correct SIDM relic
density via freeze-out. The setup thereby encompasses astrophysical as well as
cosmological aspects of light DM while simultaneously providing a solution to
the origin of light neutrino mass. Due to such connection to several frontiers,
there exist exciting discovery prospects in terms of direct and indirect search
of DM, laboratory and cosmology based dark photon signatures and effective
light neutrino mass.
