{"knowledge_schema": {"broad_category": "Physics \u2192 Astrophysics \u2192 Particle Interactions", "refinement": "This problem involves understanding the interactions between high-energy gamma rays and the Cosmic Microwave Background (CMB) radiation, specifically focusing on the annihilation process that produces electron-positron pairs.", "specific_scope": "The task is to determine the threshold energy of gamma rays that would lead to significant interactions with CMB photons, thereby limiting their lifetimes in the universe due to the \u03b3\u03b3\u2192 e^+e^- process.", "goal": "Calculate the minimum energy of gamma rays required for their lifetimes to be affected by interactions with CMB photons."}, "summary": "This problem pertains to particle interactions in astrophysics, specifically the annihilation of high-energy gamma rays with photons from the Cosmic Microwave Background (CMB) radiation. The goal is to find the threshold energy of gamma rays that would lead to significant pair production (electron-positron) interactions, thus limiting their lifetimes in the universe. Given that the average photon energy of the CMB is 10^-3 eV, the task involves calculating the energy at which the interaction becomes relevant, leading to the identification of the correct energy threshold from the provided candidates."}