Dark Photon Light Relics: Resonant Conversion Epochs in a Plasma History with a Temperature Ceiling

Resonance temperatures are 1.00e-05 eV for a mass of 10^-6 eV, 1.00e-01 eV for 10^-2 eV, and 1.00e+03 eV for 100 eV. Even the largest of these is only a fraction 3.54e-20 of the ceiling at the middle mass, and the ceiling itself is 2.82e+18 eV, set by the bound density of 9.72e+54 g per cubic centimetre. Extrapolating the linear relation, resonant production closes only for masses near 10^17 eV, far above any mass for which the dark photon would act as a light relic. Within the entire light-relic program, the resonant channel is therefore fully available in the bounced history. This study is computed from stated assumptions and published comparison values; it is not a measurement.