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

The Hubble constant $H_0$ and matter density ${\mathrm{\Omega }}_m$ 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 ${\mathrm{\Omega }}_m=0.14_{-0.07}^{+0.06}$. 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 $\Omega_{m}=0.29\pm 0.02$.