# Acoustic Dark Energy: Potential Conversion of the Hubble Tension

## TL;DR

This paper proposes a scalar field dark fluid model that converts potential to kinetic energy around matter-radiation equality, alleviating the Hubble tension by improving fit to CMB data and increasing the Hubble constant.

## Contribution

It introduces a novel scalar field mechanism that balances acoustic oscillations in dark energy, providing a new way to address the Hubble tension within the mbda CDM framework.

## Key findings

- Model improves fit to combined data by elta ext{ }.7 over mbda CDM.
- Scalar field conversion mechanism is theoretically derived and constrained.
- Future CMB polarization data can test this dark energy scenario.

## Abstract

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.