The Kerr Constant from Artian Geometry and Quantum Traction Theory

Standard optics treats the electro-optic Kerr constant K (Δn = λKE²) as a measured material coefficient, tabulated per liquid, glass, wavelength and temperature. This paper gives the Quantum Traction Theory (QTT) reading of the same object. From Artian geometry, the A4 real U(1) phase dial, A6 finite capacity, and A7 same-universe bundle closure, three features of the Kerr law are derived rather than assumed: (i) the field-induced birefringence source is the unique trace-free dyad E_iE_j − (1/3)E²δ_ij; (ii) the response is quadratic in E because the access spend is field energy, not a fitted coefficient; and (iii) the laboratory coefficient factorizes as K_lab = (cos(π/8) / F_drift)·𝔄_K, into a fixed, parameter-free substrate rail — the same cos(π/8) two-clock projection used in the QTT Faraday, Sagnac and cosmological sectors — times a material polarizability rail 𝔄_K. The material rail is a separate computation from independent inputs and is forbidden, by an explicit no-smuggling derivative ∂𝔄_K/∂K_obs = 0, from ever using the measured Kerr value. The decisive parameter-free test is the ratio K_A/K_B, in which the universal rail cancels and only the material polarizability ledger remains exposed. Version 2.0 adds per-item references to the QTT main book v10.01, corrects the Faraday cross-reference to a consistency statement (not a measurement), fixes F_drift = 1 for static Kerr cells, and hardens the no-fitted-drift guardrail.