Abstract
New measurements of the expansion rate of the universe have plunged the
standard model of cosmology into a severe crisis. In this letter we propose a
simple resolution to the problem. We propose that a first order phase
transition in a dark sector in the early universe, before recombination, can
resolve the problem. This will lead to a short phase of a New Early Dark Energy
(New EDE) component and can explain the observations. Fitting our model to
measurements of the Cosmic Microwave Background, Baryonic Acoustic
Oscillations, and supernovae yields a significant improvement of the best fit
compared with the standard cosmological model without EDE at the cost of only
two extra parameters. We find the mean value of the present Hubble parameter in
the New EDE model to be $H_0=70.9 1.0 ~km\, s^-1\,
Mpc^-1$.
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