Approaches to photon absorption in a Lorentz invariance violation scenario

Very high-energy astrophysical gamma rays suffer a suppression of their flux along their propagation due to their interaction, through the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>γ</a:mi><a:mi>γ</a:mi><a:mo stretchy="false">→</a:mo><a:msup><a:mi>e</a:mi><a:mo>+</a:mo></a:msup><a:msup><a:mi>e</a:mi><a:mo>−</a:mo></a:msup></a:math> pair-production process, with the soft photon backgrounds present in the Universe. We examine the Universe’s transparency to gamma rays within a Lorentz invariance violation (LIV) framework, focusing on photon subluminal quadratic corrections driven by a high-energy scale. Based on an explicit calculation, we provide a new expression for the cross section that overcomes the limitations of previous approaches and refines existing constraints for the LIV scale, while we introduce a new approximation that may be useful in LIV scenarios beyond effective field theory. These improvements appear essential for setting constraints on LIV effects with future observations at ultrahigh energies, where previous approximations may fall short. Published by the American Physical Society 2024