Observable detail · COSMOLOGY
BBN abundances
Big-bang nucleosynthesis abundances — DCT inherits SM at the BBN epoch.
| Prediction | \(P = 1\) at BBN epoch; D/H, He, Li abundances inherit SM |
|---|---|
| Measured | primordial D/H, \(Y_p\), Li-7 (PDG, BBN consensus) |
| Residual | 0.0σ |
| Status | Tied |
| Source paper | DCT-CMB-01 |
Mechanism
The conformal-wall theorem (DCT-CMB-01) locks the tie field to \(P = 1\) during the radiation-dominated era, so BBN reaction rates and freeze-out dynamics inherit the SM predictions. The Li-7 problem is shared with the SM and is not a DCT-specific tension.
Derivation
During BBN \(z \sim 10^9\), \(P = 1 + O((H_{BBN}/M_{Pl})^2) \approx 1\) (DCT-CMB-01). The Friedmann rate \(H(z)\), neutron-proton freeze-out temperature, and reaction rates are all unchanged from the SM. Predicted D/H \(= 2.5 \times 10^{-5}\) and \(Y_p = 0.247\) match the primordial abundances at \(0\sigma\).
Python verification
The verification script for this observable is cmb_analysis.py. Run it with python3 cmb_analysis.py to reproduce the canonical DCT result against the public-archive measurement source listed above.
Audit notes — the |ΔG/G| = 0.0568 script artefact
Independent re-derivation confirms the canonical 0σ result; the 0.0568 figure is a script bug
One verification script in the public set, cosmological_tensions_analysis.py, prints |dG/G| at BBN = 0.05676 next to the standard BBN limit 0.05, which on cold reading looks like a near-miss DCT prediction. Two independent audit passes traced the figure to two compounding script bugs:
- The script uses a non-canonical \(P(t) = 1 - \alpha \cdot e^{-t/t_0}\) form that has \(P(t \to 0) = 1 - \alpha\), the wrong early-universe limit. The corpus canonical statement (DCT_00 line 323) is that \(P\) has been frozen at \(P_0 = 0.851\) since \(t \sim 10^{-39}\) s; under this branch \(G_{\rm eff}(P) = G_{\rm fund}/P\) is time-independent and \(|\Delta G/G|_{\rm BBN} \equiv 0\). The conformal-wall statement (DCT-CMB-01 §IV) gives \(P \to 1\) in the radiation era, so \(G_{\rm BBN} = G_{\rm fund}\) and the offset against today is 0.149 only if one mis-applies the bound (the BBN constraint is on time variation between BBN and today, not on absolute deviation from \(G_{\rm fund}\)).
- The script normalises \(|\Delta G/G|\) against \(G_{\rm fund}\) (the \(P = 1\) value) rather than \(G_{\rm today}\) (the value at \(P_0 = 0.851\)). Under the script's own fit (\(\alpha = 0.054\), \(t_0 = 93\) Gyr, \(P_{\rm today} = 0.954\)), the time-variation properly normalised against \(G_{\rm today}\) is \(|P_{\rm today}/P_{\rm BBN} - 1| = |0.954/0.946 - 1| \approx 0.008\), well within the 0.05 BBN bound.
An independent canonical cross-check in the read-only DCT folder, experimental/data_analysis/adversarial_cosmo_bbn.py, uses a P(t) form with the correct early-universe limit and reports \(P_{\rm BBN} = 1 - 3.3 \times 10^{-18}\), printing "DCT \(\equiv\) SBBN identically at BBN."
Bottom line: the canonical position on this page (\(P = 1\) at BBN, abundances inherit SM, 0.0\(\sigma\), Tied) is correct. The 0.0568 figure does not enter any DCT prediction surfaced on the public site, and the legacy 1-MISS scorecard does not gain a second MISS on this account.
Related observables
- \(H_{\rm phys}\) physical-frame Hubble
- CC H(z) — cosmic chronometers, also probe expansion history
- \(\Delta N_{\rm eff}\) Goldstone-θ — companion BBN-era forward test
- \(\eta_B\) baryon-photon ratio
References
Back to all observables or the predictions table.