Weak Lensing Peaks Absence

Weak gravitational lensing convergence maps, constructed from the shapes of background galaxies, show peaks — local maxima in the projected mass distribution — corresponding to galaxy clusters and groups along the line of sight. The number counts of these convergence peaks as a function of signal-to-noise threshold are sensitive to the abundance of massive structures and therefore to the combination σ₈(Ω_m/0.3)^0.5 known as S₈. Several weak lensing surveys, including KiDS and HSC, find that the observed peak counts are lower than predicted from Planck CMB-calibrated ΛCDM models across a range of thresholds, with the deficit being most significant at high signal-to-noise (corresponding to the most massive structures). This absence of high-amplitude convergence peaks is consistent with the broader S₈ tension but provides an independent and complementary measurement of the structure growth amplitude that does not rely on two-point statistics.

Successive Collision Theory explains the deficit of high-amplitude weak lensing convergence peaks through the locally suppressed structure growth caused by the enhanced Λ_eff within the KBC supervoid. In SCT, the effective expansion rate in the local universe is elevated above the globally averaged value from the CMB, and this enhanced expansion rate partially counteracts gravitational infall on all scales within the void. The growth of matter perturbations is suppressed by the enhanced Λ_eff in the same way that a cosmological constant suppresses growth — by providing an additional repulsive contribution to the Friedmann equation that reduces the growth factor f = d ln δ/d ln a. The highest-amplitude convergence peaks, corresponding to the most massive clusters, are most sensitive to this growth suppression because their abundance is exponentially sensitive to the matter power spectrum amplitude. The SCT prediction is therefore a deficit in massive cluster counts — and hence convergence peak counts — that is largest at the highest signal-to-noise thresholds, consistent with observations.

The gravitational superposition mechanism introduces a competing effect that partially compensates the growth suppression at intermediate scales: it adds effective gravitational influence that boosts the convergence at the positions of existing clusters while not creating new clusters. The net effect on peak counts is a reduction in the number of peaks above the highest thresholds (where new cluster formation is suppressed) combined with a slight broadening of the convergence distribution around existing clusters (where superposition adds to the lensing signal). This produces a specific shape change in the peak count function — a deficit at high S/N with a slight excess at intermediate S/N — that is a unique SCT prediction distinguishable from a simple uniform rescaling of σ₈ or from a warm dark matter free-streaming suppression that affects small-scale power uniformly.