He-4 Abundance

The primordial helium-4 mass fraction Y_p is one of the four light element benchmarks of BBN, predicted to be Y_p ~ 0.247 from standard BBN using the Planck baryon density. Measurements of Y_p in metal-poor extragalactic HII regions — where the helium abundance has been least contaminated by stellar nucleosynthesis — have historically shown a mild tension with this prediction, with some analyses preferring slightly higher values around Y_p ~ 0.2551 ± 0.0022 while others recover values consistent with the standard prediction. The tension, when present, suggests either a higher expansion rate during BBN (more relativistic species increasing the freeze-out temperature), a higher baryon density than Planck infers, or systematic errors in the emission line analysis of metal-poor nebulae. The sensitivity of Y_p to the effective number of relativistic species N_eff makes this measurement a key probe of BSM physics, yet the SCT framework addresses it without invoking new particle species.

Successive Collision Theory addresses the helium-4 abundance through its modification of the effective expansion rate during the BBN epoch. In SCT, the collision thermalization event deposited kinetic energy into the photon-baryon plasma instantaneously, establishing the initial conditions for BBN with a specific baryon-to-photon ratio η and a specific radiation energy density. The tensor mesh of the overlapping nested frame hierarchy contributes a smooth, distributed gravitational energy density to the total energy budget at all epochs including BBN. This superposition contribution to the stress-energy tensor enters the Friedmann equation as an additional effective energy density during the radiation-dominated epoch, modestly increasing the Hubble rate H(z) at z ~ 10⁸ compared to the pure radiation-plus-matter standard model. A slightly higher H at BBN temperatures shifts the neutron freeze-out temperature upward, increasing the neutron-to-proton ratio at freeze-out and therefore boosting the helium-4 yield.

The magnitude of the gravitational superposition contribution to H during BBN is small — at the level of a fraction of a percent in energy density — but is physically determined by the same superposition term that explains the lensing amplitude excess A_lens > 1 and the S₈ tension at late times. SCT therefore predicts a correlated set of signatures: a mild helium-4 excess above the pure BBN prediction, an elevated A_lens in the CMB, and an enhanced S₈ clustering amplitude, all arising from the same gravitational superposition mechanism at different epochs. The fact that all three observations show mild excesses in the same direction provides a coherent multi-epoch test of the superposition contribution to the stress-energy tensor — a prediction unique to SCT that no single-parameter modification of ΛCDM can simultaneously reproduce.