Cosmic Microwave Background Spectral Distortion Limits on Primordial Black Holes

Before the cosmic microwave background was released at recombination, the universe was an almost perfect blackbody machine, but not quite a perfect one. Energy injected into the photon bath at redshifts between about two million and fifty thousand cannot fully thermalise; it leaves a characteristic chemical-potential distortion of the spectrum, and later injections leave a Compton-y distortion instead. The headline computed values are: strongest finite f = 1.84e-04. The study is a computation from stated assumptions, not a measurement, and the deposited script reproduces every number quoted.