Acoustic Dark Energy: Potential Conversion of the Hubble Tension
  We discuss the ability of a dark fluid becoming relevant around the time of
matter radiation equality to significantly relieve the tension between local
measurements of the Hubble constant and CMB inference, within the $\Lambda$CDM
model. We show that the gravitational impact of acoustic oscillations in the
dark fluid balance the effects on the CMB and result in an improved fit to CMB
measurements themselves while simultaneously raising the Hubble constant. The
required balance favors a model where the fluid is a scalar field that converts
its potential to kinetic energy around matter radiation equality which then
quickly redshifts away. We derive the requirements on the potential for this
conversion mechanism and find that a simple canonical scalar with two free
parameters for its local slope and amplitude robustly improves the fit to the
combined data by $\Delta\chi^2 \approx 12.7$ over $\Lambda$CDM. We uncover the
CMB polarization signatures that can definitively test this scenario with
future data.
