  We study interactions between polaritons formed by hybridization of excitons
in a two-dimensional (2D) semiconductor with surface optical phonons or
plasmons. These quasiparticles have a high effective mass and can bind into
bipolaritons near a Feshbach-like scattering resonance. We analyze the phase
diagram of a many-body condensate of heavy polaritons and bipolaritons and
calculate their absorption and luminescence spectra, which can be measured
experimentally.
