“…decaying or annihilating particles [39][40][41][42][43], reionization and structure formation [44][45][46][47][48][49][50][51], primordial black holes [52][53][54], cosmic strings [55][56][57][58], small-scale magnetic fields [59][60][61][62], the adiabatic cooling of matter [19,63], cosmological recombination [64][65][66][67][68][69], gravitino decay [70], and the dissipation of primordial density perturbations [20,21,[71][72][73][74][75][76][77][78][79][80][81] which is the main concern of this paper. Types of spectral distortions are characterized by the redshifts at which energy releases to CMB photons:…”