# A new measurement of the Hubble constant and matter content of the Universe using extragalactic background light $\gamma$-ray attenuation

## TL;DR

This paper introduces a novel method using gamma-ray attenuation from extragalactic background light to independently measure the Hubble constant and matter density, providing results that complement existing cosmological techniques.

## Contribution

The study presents a new approach leveraging gamma-ray attenuation data to estimate cosmological parameters, offering an independent and complementary measurement to traditional methods.

## Key findings

- Estimated Hubble constant: 67.4 km/s/Mpc with uncertainties.
- Estimated matter density: 0.14 with uncertainties.
- Combined analysis yields H0=66.6 km/s/Mpc and Ωm=0.29.

## Abstract

The Hubble constant $H_{0}$ and matter density $\Omega_{m}$ of the Universe are measured using the latest $\gamma$-ray attenuation results from Fermi-LAT and Cherenkov telescopes. This methodology is based upon the fact that the extragalactic background light supplies opacity for very high energy photons via photon-photon interaction. The amount of $\gamma$-ray attenuation along the line of sight depends on the expansion rate and matter content of the Universe. This novel strategy results in a value of $H_{0}=67.4_{-6.2}^{+6.0}$~km~s$^{-1}$~Mpc$^{-1}$ and $\Omega_{m}=0.14_{-0.07}^{+0.06}$. These estimates are independent and complementary to those based on the distance ladder, cosmic microwave background (CMB), clustering with weak lensing, and strong lensing data. We also produce a joint likelihood analysis of our results from $\gamma$ rays and these from more mature methodologies, excluding the CMB, yielding a combined value of $H_{0}=66.6\pm 1.6$~km~s$^{-1}$~Mpc$^{-1}$ and $\Omega_{m}=0.29\pm 0.02$.