A Geometric Prediction for the Tau Anomalous Magnetic Moment

We present a zero-parameter geometric formula for the tau anomalous magnetic moment, based on tetrahedral combinatorics. The formula predicts a_τ = 0.0011758018, consistent with the Standard Model range of 0.0011758–0.0011768. The geometric coefficient 48(1+α) derives from the permutation and chirality of a four-loop spatial quadrilateral embedded in a regular tetrahedron. Due to the current ~2% experimental uncertainty in a_τ, this prediction is not yet distinguishable from an alternative coefficient 51(1+α), which is related to the tau mass ratio formula. Future tau g−2 measurements at 0.1% precision will provide a decisive test.