Studying cosmological $\gamma$-ray propagation with the Cherenkov Telescope Array

Understand

The measurement of $\gamma$-rays originating from active galactic nuclei offers the unique opportunity to study the propagation of very-high-energy photons over cosmological distances.

• Most prominently, $\gamma$-rays interact with the extragalactic background light (EBL) to produce $e^+e^-$ pairs, imprinting an attenuation signature on $\gamma$-ray spectra.
• The $e^+e^-$ pairs can also induce electromagnetic cascades whose detectability in $\gamma$-rays depends on the intergalactic magnetic field (IGMF).
• Furthermore, physics beyond the Standard Model such as Lorentz invariance violation (LIV) or oscillations between photons and weakly interacting sub-eV particles (WISPs) could affect the propagation of $\gamma$-rays.