Helium-4 Yield in a Torsion-Regulated Bounce: A Lower Bound on the Bounce Temperature

The observed primordial helium-4 mass fraction, near 0.245 with an uncertainty of a few parts in a thousand, is the oldest quantitative probe of the hot early universe. The calculation finds that a bounce temperature of 3.0 MeV or higher keeps the predicted yield within the stated observational tolerance around 0.245, while a bounce at 2 MeV would give 0.2365 and a bounce at 8 MeV would give 0.2449, against the standard value 0.245. The bound is modest in energy yet sharp in implication: the turnaround must be separated from nucleosynthesis by at least the stated factor in temperature, or the oldest abundance in cosmology would already have recorded it. Computed from stated assumptions, not measured.