  Assisted annihilation is a novel mechanism to generate viable sub-GeV thermal
dark matter, where a pair of stable dark matter annihilates with an assister to
Standard Model states. Typically such $3 \to 2$ annihilation topologies are
flux suppressed compared to $2 \to 2$ processes. In this paper, we explore the
possibility of a resonant $3 \to 2$ assisted annihilation dominantly driving
the freeze-out of dark matter. We demonstrate that in a simple multipartite
scalar extension of the Standard Model this can be realized in certain regions
of parameter space to provide viable dark matter relic density, in agreement
with observation. We demonstrate that for photophilic assisters parts of the
parameter space are already constrained by indirect detection experiments and
the measurements of CMB anisotropies while substantial regions remain beyond
the present limit.

High Energy Physics - Phenomenology