Foam-Plexus Interpretation of Nonlinear Isotope Shifts in Calcium

Precision isotope-shift spectroscopy in calcium (Phys. Rev. Lett. 134, 233002, 2025) has re-

vealed nonlinear deviations in King plots at∼ 103σ significance, suggesting either underestimated

nuclear-structure effects or a new short-range electron–neutron interaction. Within the Foam-Plexus

framework, we show that such deviations arise naturally from mesoscale cross-correlations between

electromagnetic and gravity/weak plexuses inside the nuclear region. These correlations introduce a

screened Yukawa-like potential without requiring a new boson, with the effective coupling emerging

from Planck-scale foam diluted over atomic scales. The resulting curvature pattern predicts isotope-

dependent scaling tied to neutron skins and transition-specific electron overlap, providing falsifiable

distinctions from conventional new-boson hypotheses.