The Hubble Constant Troubled by Dark Matter in Non-Standard Cosmologies

TL;DR

This paper explores how non-standard cosmologies with non-thermal dark matter production can reconcile the discrepancy between local and CMB measurements of the Hubble constant, suggesting a higher H0 value.

Contribution

It demonstrates that non-thermal dark matter production mechanisms can increase the Hubble constant within the ΛCDM framework, resolving the Hubble tension.

Findings

Non-thermal dark matter production can raise H0 to 70-74 km/s/Mpc.

Non-standard cosmologies reconcile CMB and local H0 measurements.

The approach alleviates the Hubble tension without abandoning ΛCDM.

Abstract

The Standard Cosmological Model has experienced tremendous success at reproducing observational data by assuming a universe dominated by a cosmological constant and dark matter in a flat geometry. However, several studies, based on local measurements, indicate that the universe is expanding too fast, in disagreement with the Cosmic Microwave Background. Taking into account combined data from CMB, Baryon Acoustic Oscillation, and type Ia Supernovae, we show that if the mechanism behind the production of dark matter particles has at least a small non-thermal origin, one can induce larger values of the Hubble rate $H_0$, within the $\Lambda$CDM, to alleviate the trouble with $H_0$. In the presence of non-standard cosmology, however, we can fully reconcile CMB and local measurements and reach $H_0=70-74\, {\rm km s^{-1} Mpc^{-1}}$.