What is the Leakage Theory?

The Leakage Theory is a speculative 5D braneworld hypothesis. It proposes that our 4D universe is a brane in a higher-dimensional bulk, and that a single early-universe 'Radion Leakage Event' near redshift z ≈ 50,000 imprinted an exponential cutoff on the small-scale matter power spectrum. The same event is offered as a candidate explanation for the S₈ tension and the Lyman-α small-scale power suppression. (Updated in v1.7.2: an earlier version of this answer also cited JWST early massive galaxies; spectroscopy of JWST's 'little red dots' now indicates they are supermassive black holes in dense gas cocoons rather than anomalously early galaxies, so that framing has been retracted.)

Does it claim ΛCDM is wrong?

No. The claim is that ΛCDM is incomplete — it is missing one early-universe event. With that event added, several independent tensions soften at once, without bespoke fixes for each. ΛCDM is recovered as a limit everywhere it already works (CMB acoustic peaks, BBN, large-scale linear structure).

What are JWST's 'Red Monsters'?

'Red Monsters' / 'little red dots' was the informal name given to a population of unusually red, compact sources JWST began finding at high redshift (z ≈ 5–14). They were initially interpreted as anomalously massive early galaxies. Spectroscopic follow-up (GLIMPSE-17775, 2026) indicates these objects are instead supermassive black holes in dense gas cocoons — early-universe AGN consistent with what ΛCDM predicts. The Leakage Theory no longer treats them as a tension to explain. (Updated in v1.7.2.)

What is the Hubble tension?

The Hubble tension is the persistent ~5σ disagreement between the local measurement of the Hubble constant H₀ (from supernovae and Cepheids, around 73 km/s/Mpc) and the value inferred from the cosmic microwave background under ΛCDM (around 67 km/s/Mpc). The gap has grown, not closed, with better data.

What is the S₈ tension?

S₈ tension is the persistent finding that the late-time universe appears smoother — less clumpy on small scales — than the early-universe CMB extrapolated under ΛCDM predicts. Weak-lensing surveys (KiDS, DES, HSC) consistently land on a lower S₈ than Planck expects.

Why one event instead of a continuous modification?

The data favours something localized in time. A continuous modification would leave smooth fingerprints across the expansion history that we do not see. A short, sharp event leaves a step-like imprint, which is closer to what the observations look like.

What would falsify the Leakage Theory?

A precise measurement of the linear matter power spectrum at k ≈ 0.5–1 h·Mpc⁻¹ showing standard ΛCDM behaviour with no exponential cutoff would directly contradict the central prediction. Independently, a tighter constraint on the early expansion history near z ≈ 50,000 — for example from PIXIE-class CMB spectral distortion measurements — that rules out a brief deviation in H(z) at that epoch would also kill the proposed event.

Has this been peer reviewed?

No. It is an independent, in-progress hypothesis published openly as an educational explainer specifically to invite criticism and collaboration. Decisive tests — modified Boltzmann-code analysis with CLASS or CAMB, and N-body simulations — have not yet been run.

Why z ≈ 50,000 specifically? Isn't that ad hoc?

It is the redshift at which the model's expansion-history modification best fits the small-scale suppression behind S₈ and the Lyman-α forest simultaneously. It was not chosen by hand — it is where two independent observational constraints intersect. (Updated in v1.7.2: the earlier version of this answer also cited the JWST early-galaxy abundance as a joint constraint; that input has been removed since the JWST 'red dots' are now identified as AGN, not anomalous galaxies.)

Wouldn't an extra scalar field mess up Big Bang Nucleosynthesis?

Only if it has significant energy density during BBN. In this model the Radion is stabilised and quiet through BBN; the proposed leakage event happens later, near matter–radiation equality, so BBN predictions are preserved.

How is this different from warm or fuzzy dark matter?

Warm and fuzzy dark matter produce a small-scale cutoff by changing the dark-matter particle. The Leakage model leaves dark matter alone and modifies the early expansion history through a brief geometric event, so it preserves linear growth above the cutoff in a way WDM/FDM do not. Future surveys can distinguish the signatures.

How does the model evade fifth-force constraints?

The Radion couples only to the trace T^μ_μ of the stress-energy tensor. For relativistic species the trace is essentially zero, and for ordinary low-energy matter it is small, so the effective force is negligible at the scales probed by Cassini, lunar laser ranging and sub-millimetre inverse-square-law tests.

What about the laboratory anomalies mentioned in Level 3?

Some reported anomalous forces in asymmetric-capacitor experiments remain unexplained in standard physics. This model offers one speculative interpretation of how such effects could arise if the T^μ_μ coupling is real, but that laboratory interpretation is independent of the cosmological claim and is not a prediction.

What is the Radion stabilisation mechanism?

The model assumes a Goldberger–Wise-style mechanism — a bulk scalar with a potential that gives the Radion a mass and a stable minimum — with the leakage event treated as a transient excursion followed by damped return. Working this out in full detail is one of the explicit open problems in the Roadmap section.

Is Brick 4 derived from first principles?

Not yet. Brick 4 (scale selection) shows that one potential can produce three 0.75 values, but we've fitted its parameters to observations. We haven't solved the full 5D Einstein equations to derive these values independently. That's Stage 3 of the validation roadmap (3–6 months of work requiring 5D expertise). (Added in v1.8.1.)

What's the difference between 'phenomenological' and 'derived'?

Derived means we solved the equations from first principles and the result came out naturally. Phenomenological means we chose parameters to match observations, which is valid science but not yet proof of deep structure. Brick 4 is currently phenomenological; Bricks 1–3 are derived. (Added in v1.8.1.)

Is the model circular reasoning?

Brick 4 has three parameters and three observational constraints, so it's 'fit to zero degrees of freedom' — self-consistent but not independently testable yet. That's why Stage 1 (Boltzmann validation) is critical: we run the code with fixed parameters and check if σ₈ comes out right. If it does, the mechanism is real. (Added in v1.8.1.)

When will you know if the model is wrong?

Multiple clear tests: (1) if σ₈ is higher than ΛCDM (not lower), (2) if Lyman-α shows no suppression, (3) if the growth rate is unchanged, (4) if CMB damping is suppressed by more than 5%. Any of these would kill the model. All are testable within 2–3 years. (Added in v1.8.1.)

Seven-Brick Framework — Technical Details & Derivations

The Leakage v2.0.0