A Big Bang Nucleosynthesis Consistency Test of the CCC+TL Cosmology

We investigate whether Big Bang nucleosynthesis (BBN) remains compatible with the covarying coupling constants plus tired light (CCC+TL) cosmology. In this framework, only quantities with explicit length dimensionality covary through a universal scaling function f(z), while dimensionless constants and dimensionless ratios remain invariant. At the redshifts z relevant to BBN, f(z) approaches a constant plateau fmax≃3, and the tired light contribution is negligible, so the early-time dynamics reduce to a global rescaling of dimensioned quantities. In particular, the Hubble expansion rate H at fixed temperature T satisfies HCTL(T)=fmax−1HΛCDM(T), implying a longer cooling time Δt between weak freeze-out and the onset of nucleosynthesis by the same factor (CCC+TL labelled as CTL). We find that BBN predictions are preserved, provided the relevant interaction rates Γ and decay rates governing the neutron lifetime τn share the same plateau scaling as H, so that governing combinations such as Γ/H and exp (−Δtτn)  remain invariant. Implementing these plateau rescalings in the Kawano/NUC123 network (via a single control parameter fctl ≡fmax) yields identical light-element abundances for fctl =1 (ΛCDM) and fctl =3(CCC+TL) to within 10−3−10−4 level, consistent with numerical rounding. We also illustrate that adopting the lower late-time CCC+TL baryon density from Pantheon+ data fit can reduce the 7Li discrepancy but simultaneously increases D/H, implying that BBN alone does not select between the late-time baryon density inferences considered here.