A solution to the Hubble tension with self-interacting ultralight dark matter

TL;DR

This paper proposes that oscillations of self-interacting ultralight dark matter can act as extra radiation before recombination, reducing the sound horizon and increasing the Hubble constant, potentially resolving the Hubble tension.

Contribution

It introduces a novel dark matter model with specific self-interactions that naturally addresses the Hubble tension without exotic components.

Findings

Oscillations act as extra radiation before recombination.

Reduction of the sound horizon increases the Hubble constant.

Model is consistent with current astronomical constraints.

Abstract

We show that oscillations of self-interacting ultralight dark matter with a characteristic energy scale $ \tilde{m} \simeq 1~eV $ naturally act as an extra radiation component just before the recombination era, decreasing the sound horizon radius of the photon-baryon fluid. This reduction leads to an increase in the present-day Hubble parameter, potentially resolving the Hubble tension without the need for exotic matter or energy. The required mass and quartic self-interaction coupling are consistent with current astronomical constraints, including the relic dark matter density. This model could also reduce the $S_8$ tension often associated with other early-time solutions.