  The near equality of the dark matter and baryon energy densities is a
remarkable coincidence, especially when one realizes that the baryon mass is
exponentially sensitive to UV parameters in the form of dimensional
transmutation. We explore a new dynamical mechanism, where in the presence of
an arbitrary number density of baryons and dark matter, a scalar adjusts the
masses of dark matter and baryons until the two energy densities are
comparable. In this manner, the coincidence is explained regardless of the
microscopic identity of dark matter and how it was produced. This new scalar
causes a variety of experimental effects such as a new force and a (dark)
matter density-dependent proton mass.
