Freezing Out Early Dark Energy

Kavli Affiliate: W. L. Kimmy Wu

| First 5 Authors: Jannis Bielefeld, W. L. Kimmy Wu, Robert R. Caldwell, Olivier Dore,

| Summary:

A phenomenological model of dark energy that tracks the baryonic and cold
dark matter at early times but resembles a cosmological constant at late times
is explored. In the transition between these two regimes, the dark energy
density drops rapidly as if it were a relic species that freezes out, during
which time the equation of state peaks at +1. Such an adjustment in the dark
energy density, as it shifts from scaling to potential-domination, could be the
signature of a trigger mechanism that helps explain the late-time cosmic
acceleration. We show that the non-negligible dark energy density at early
times, and the subsequent peak in the equation of state at the transition,
leave an imprint on the cosmic microwave background anisotropy pattern and the
rate of growth of large scale structure. The model introduces two new
parameters, consisting of the present-day equation of state and the redshift of
the freeze-out transition. A Monte Carlo Markov Chain analysis of a
ten-dimensional parameter space is performed to compare the model with
pre-Planck cosmic microwave background, large scale structure and supernova
data and measurements of the Hubble constant. We find that the transition
described by this model could have taken place as late as a redshift z~400. We
explore the capability of future cosmic microwave background and weak lensing
experiments to put tighter constraints on this model. The viability of this
model may suggest new directions in dark-energy model building that address the
coincidence problem.

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