The Temperature Ceiling Itself: Maximum Temperature of a Radiation Bath Under the Bound Density, Across Species Counts

At the Standard Model count the ceiling is 1.05e+09 GeV, or 1.21e+22 K. The species dependence is weak, as the fourth root requires: at g* = 10.75 the ceiling rises to 1.86e+09 GeV, and even a thousand relativistic species lower it only to 5.97e+08 GeV. The carrier dependence is the opposite story: the electron branch would place the ceiling at 2.44e+07 GeV, nearly three orders of magnitude lower, which would rewrite the conclusions of every high-scale transition study. The ceiling used throughout this territory therefore stands or falls with the carrier-selection argument, and that argument, confinement of the spin carrier with the matter whose density is being bounded, is the load-bearing assumption readers should examine first. This study is simulated and computed from stated assumptions; it is not a measurement.