Bubble-Wall Velocities With a Density Ceiling: Detonation, Deflagration and the Chapman-Jouguet Bound Revisited

The Chapman-Jouguet velocity rises from 0.653 at alpha = 0.01 through 0.777 at alpha = 0.1 to 0.934 at alpha = 1, approaching the speed of light only for strengths far beyond those realised in electroweak-scale models. The ceiling permits a maximum strength of alpha_max = 1.19e+28 at 100 GeV. Because that maximum lies many orders of magnitude above any strength contemplated for a thermal transition at this temperature, no wall regime is excluded by the ceiling at the electroweak scale: deflagrations, hybrids, and detonations all remain kinematically available, and model selection among them must come from friction and microphysics rather than from the bound. Stated differently, the ceiling bounds alpha in principle while leaving the phenomenologically relevant interval entirely intact. This study is simulated and computed from stated assumptions; it is not a measurement.