# COSMO19

Sep 2 – 6, 2019
Europe/Zurich timezone

## Acoustic Dark Energy: Potential Conversion of the Hubble Tension

Sep 4, 2019, 5:50 PM
20m
Talk Modified Gravity and Dark Energy

### Speaker

Mr Meng-Xiang Lin (University of Chicago)

### Description

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 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.

### Primary author

Mr Meng-Xiang Lin (University of Chicago)

### Co-authors

Prof. Wayne Hu (University of Chicago) Dr Marco Raveri (University of Chicago) Mr Giampaolo Benevento (Universit\`a degli Studi di Padova)