Speaker
Description
The extragalactic background light (EBL) encodes the signature of galaxy evolution and photon production history since the epoch of reionization. The optical and infrared photons that dominate the EBL can interact with 𝛾-rays above a certain energy threshold to create e+/e- pairs, leading to absorption imprints seen in the very-high energy (VHE; E > 100 GeV) spectra of extragalactic sources. The past decades of 𝛾-ray astronomy have recently enabled the first purely parametric 𝛾-ray measurement of the EBL spectrum at $z = 0$. In this work, we show how this 𝛾-ray cosmology result can be extended to explore both particle physics and cosmology, when combined with EBL estimates from deep field surveys. Assuming axion-like particles (ALPs) make up the entirety of dark matter, we derive new constraints on the coupling constant between ALPs and photons, over an energy range broader than typically observed by the Hubble space telescope. Furthermore, we measure the local Hubble constant independently from both cosmic microwave background observations and cosmic distance ladder estimates, with precision greater than the current gravitational waves constraints. These results highlight the potential of 𝛾-ray cosmology with the current generation of instruments, setting the stage for the next generation instruments, the Cherenkov Telescope Array Observatory (CTAO).