Cosmological signatures of a Rapid Diluted Energy Density
  We study the cosmological signatures of having extra energy density,
$\rho_{ex}$, beyond the $\Lambda$CDM model that dilutes rapidly, faster than
radiation, at a scale factor $a_c$ with a corresponding mode $k_c=a_c H(a_c)$
crossing the horizon at that time. These types of models are motivated by phase
transitions of the underlying elementary particles, for example the creation of
protons and neutrons from almost massless quarks or the recently proposed Bound
Dark Energy model. The rapidly dilution of $\rho_{ex}$ leaves distinctive
imprints in the Universe not only in the expansion history with a clear impact
on the acoustic scale, $r_s(a_cc)$, and angular distances, $D_A(a)$, but also
in the matter and CMB power spectra. The rapidly diluted energy density
$\rho_{ex}$, (RDED) generates characteristic signatures that can be observed
with current and future precision cosmological data. In particular, we find a
bump in the matter power spectrum compared to the standard $\Lambda$CDM. We
identify the amplitude, width, and time scale of the bump to the physical
properties of the transition. We study these effects with linear theory,
standard perturbation theory, and the correlated impact on cosmological
distances, allowing for independent measurements of these extensions of the
standard $\Lambda$CDM model.
