Revisiting $\gamma\gamma$ absorption for UHE photons with $l\bar{l}$ and $q\bar{q}$ production.

We revisit the estimate of cosmic opacity to ultra-high energy (UHE) $\gamma$ rays ($E>10^{18}$ eV) considering, besides the $\gamma \gamma \to e^+e^-$ and $\gamma \gamma \to e^+ e^- e^+ e^-$ processes, the production of other leptons ($l$) and quarks ($q$). The most important channels are those leading to the production of light $q\bar{q}$ ($q=u,d$) followed by hadronization and $\mu^{\pm}$, while the production of $\tau^{\pm}$ and $s\bar{s}$, $c\bar{c}$ followed by hadronization are subdominant. We consider also the single neutral meson production but it does not play a significant role. We recalculate the optical depth by considering all these processes, and we find that at UHE absorption is currently underestimated. For a distance $\simeq 130$ Mpc (approximately equal to the GZK radius) the photon survival probability is smaller by about one order of magnitude with respect to the current estimates.