Deuterium Scatter

While the mean primordial deuterium abundance from high-redshift quasar absorption systems is well-measured, there is an intrinsic scatter in the D/H values across different absorption systems that exceeds what pure observational uncertainties would predict. Some analyses of individual systems find D/H values ranging from 2.2 × 10⁻⁵ to 2.8 × 10⁻⁵ — a spread of ~25% around the mean — with no obvious correlation with the absorber's metallicity, column density, or redshift. In standard ΛCDM, all primordial gas should have the same D/H set by the universal η, and any scatter should arise purely from observational systematics or from small amounts of stellar deuterium destruction at low metallicity. The observed scatter therefore challenges the assumption of a universal primordial D/H, implying either that η varied spatially, or that an early deuterium-modifying process operated inhomogeneously in the early universe.

Successive Collision Theory provides a natural physical origin for the intrinsic D/H scatter through the inhomogeneous mixing of pre-existing processed material with freshly BBN-synthesized deuterium in the collision debris field. The angular momentum gradients and density contrasts set by the collision geometry produced spatial inhomogeneities in the debris field: some regions were enriched by pre-existing stellar ejecta (which destroys deuterium) while others retained more pristine BBN products depending on the local ratio of thermalized pre-existing material to freshly synthesized plasma. Quasar absorption systems that lie along lines of sight through different regions of this inhomogeneous debris field therefore sample different effective D/H values, producing an intrinsic scatter that reflects the spatial variation in the pre-existing/BBN mixing ratio.

The SCT prediction for deuterium scatter is that it should be correlated with other pre-collision abundance signatures in the same absorption systems: absorbers with lower D/H (more pre-existing stellar contamination) should also show slightly elevated Be, higher ³He from pre-collision AGB ejecta, and metallicity that is slightly higher than expected from purely post-collision stellar nucleosynthesis at the same redshift. The correlated abundance pattern across multiple elements provides a multi-dimensional test that distinguishes the SCT inhomogeneous mixing explanation from a spatially varying η explanation, which would affect only the BBN products without introducing the correlated signature of pre-existing stellar nucleosynthesis products.