Unification of General Relativity and Quantum Mechanics via Foundational D1 Field Theory Series I, Paper II: Newton's Constant from D1 Boundary Normalisation

This paper is the second in a three-paper series developing the classical gravity pillar of foundational D1 field theory. Series I, Paper I showed how spacetime geometry and Einstein-type gravitational dynamics can arise from the stable unfolded phase of the D1 field. In that low-energy regime, the non-minimal curvature coupling of the D1 field reduces to an Einstein-Hilbert-type curvature term and gives an effective gravitational coupling. The present paper addresses the remaining normalisation problem: why the effective gravitational coupling obtained from the D1 curvature coefficient should equal the observed Newton constant G. The central proposal is that Newton’s constant is fixed by a D1 boundary-normalisation condition. A horizon-like or horizon-associated D1 phase boundary carries a dimensionless boundary charge q_H. For the fundamental D1 boundary unit, the condition q_H = 1 fixes the normalisation parameter eta = 1. This fixes the stable D1 curvature coefficient F(v) = xi v^2 to the Einstein-Hilbert value F(v) = 1/(8 pi G), giving G_eff = G. The paper does not claim to derive the separate microscopic values of xi and v, nor does it construct the full D1 black-hole interior model. Horizons are used here only as effective normalisation boundaries. The detailed D1 treatment of black-hole transition layers, regular-core behaviour, conserved-current matching, evaporation end-states, and thermodynamic consistency is reserved for Series I, Paper III.