  Gravitational waves signatures from dynamical scalar field configurations
provide a compelling observational window on the early universe. Here we
identify intriguing connections between dark matter and scalars fields that
emit gravitational waves, either through a first order phase transition or
oscillating after inflation. To study gravitational waves from first order
phase transitions, we investigate a simplified model consisting of a heavy
scalar coupled to a vector and fermion field. We then compute gravitational
wave spectra sourced by inflaton field configurations oscillating after E-Model
and T-Model inflation. Some of these gravitational wave signatures can be
uncovered by the future Big Bang Observatory, although in general we find that
MHz-GHz frequency gravitational wave sensitivity will be critical for
discovering the heaviest dark sectors. Intriguingly, we find that scalars
undergoing phase transitions, along with E-Model and T-Model potentials, can
impel a late-time dark matter mass boost and generate up to Planck mass dark
matter. For phase transitions and oscillating inflatons, the largest dark
matter mass boosts correspond to higher amplitude stochastic gravitational wave
backgrounds.
