  We put forward a new proposal for generating the baryon asymmetry of the
universe by making use of the dynamics of a $\mathrm{U}(1)$ scalar field
coupled to dark matter. High dark matter densities cause the $\mathrm{U}(1)$
symmetry to break spontaneously so that the field acquires a large vacuum
expectation value. The symmetry is restored when the density redshifts below a
critical value, resulting in the coherent oscillation of the scalar field. A
net $B-L$ number can be generated either via baryon number-conserving couplings
to the standard model or through small symmetry-violating operators and the
subsequent decay of the scalar condensate.
