  We study the possibility of Late Forming Dark Matter (LFDM), where a scalar
field, previously trapped in a metastable state by thermal or finite density
effects, begins to oscillate near the era matter-radiation equality about its
true minimum. Such a theory is motivated generally if the dark energy is of a
similar form, but has not yet made the transition to dark matter, and, in
particular, arises automatically in recently considered theories of neutrino
dark energy. If such a field comprises the present dark matter, the matter
power spectrum typically shows a sharp break at small, presently nonlinear
scales, below which power is highly suppressed and previously contained
acoustic oscillations. If, instead, such a field forms a subdominant component
of the total dark matter, such acoustic oscillations may imprint themselves in
the linear regime.

Astrophysics;High Energy Physics - Phenomenology;High Energy Physics - Theory