Executive summary

We model our 4‑D universe as a brane embedded in a higher‑D bulk. In flat FRW the effective expansion law acquires a high‑energy ρ2 piece (controlled by the brane tension λ) and a dark‑radiation term C/a4. Two clean tests follow:

Falsifiability: the same λ must satisfy both sectors. If it fails either, the model is wrong.

Key equations

Modified Friedmann (flat, k=0)
$$ H^2 = \frac{8\pi G}{3}\,\rho\Bigl(1 + \frac{\rho}{2\lambda}\Bigr) + \frac{\Lambda_4}{3} + \frac{C}{a^4} $$
Two relations (test program)
$$ f_{\rm br}(\lambda) = \alpha\,\lambda^{1/4}, \qquad \frac{C}{\rho_{\gamma,0}} = \frac{7}{8}\Bigl(\frac{4}{11}\Bigr)^{4/3}\,\Delta N_{\rm eff} $$

Results (REALDATA pass)

Break frequency

$$ f_{\rm br} = 7.96\times10^{-9}\;\mathrm{Hz} $$

68% interval shown in plot.

Slopes

m_1 \approx -0.92,\; m_2 \approx -1.52

Convention matches the Two‑Pager notation.

Calibration placeholder

f_{\rm br}(\lambda)=\alpha\,\lambda^{1/4}

When α is set, report λ_best in physical units.

CheckValue / boundStatus
\(\Delta N_{\rm eff}\) (Planck 2018)2.99 ± 0.17used as prior
PPN \(\gamma,\beta\)[literature numbers]consistent
Binary pulsars[literature]consistent
Short‑range gravity[literature]consistent
Growth \(S_8\)[literature]consistent

Figures

PTA spectrum (quick‑look). Points & 68% band with broken PL overlay.
PTA spectrum (quick‑look). Points & 68% band with broken PL overlay.
LISA sensitivity (ESA RCL2019, 10‑yr instrument‑only).
LISA sensitivity (ESA RCL2019, 10‑yr instrument‑only).

Downloads

Place PDFs/JSON/TXT under assets/downloads/ and images under assets/images/ in your repo.

Reproducibility & DOI

The exact CSVs, JSONs and PDFs are archived on Zenodo. Use the latest version DOI: 10.5281/zenodo.16868562 (or the “all‑versions” DOI 10.5281/zenodo.16866883).

For the corners (posterior) pack or additional LISA overlays (e.g., “10‑yr + confusion” or “4‑yr variants”), see the repository or the “Related works” items on the Zenodo record.