The macroscopic consistency of non-linear massive gravity relies strictly on the de Rham-Gabadadze-Tolley (dRGT) potential to dynamically decouple the pathological Boulware-Deser ghost. However, within the standard bottom-up Effective Field Theory (EFT) paradigm, the exact parameter configuration required by the dRGT structure demands severe, dynamically unjustified fine-tuning. In this second paper of the series, we resolve this fine-tuning paradox by deriving the non-linear interaction potential of the macroscopic graviton strictly ab initio from the non-perturbative vacuum of open bosonic String Field Theory (SFT). We formally prove that the canonical phase-space stability constraint in the infrared (the absence of the ghost) is projectively isomorphic to the ultraviolet BRST gauge coherence of the fundamental SFT vacuum via the Stückelberg mapping mechanism. Consequently, the non-linear dRGT parameter subspace acts as a strict dynamical attractor. We computationally verify this theorem through a Wilsonian deep-integration protocol up to string truncation level L=8. By rigidly applying the exact geometric scaling invariant of the transverse string worldsheet (ₓ₇=1/24) without any phenomenological parameter fitting, we demonstrate that physiological low-energy EFT truncation artifacts spontaneously collapse by 61. 2\% as the continuum limit is approached. This provides the definitive mathematical and numerical proof of the intrinsic, fine-tuning-free convergence of emergent SFT gravity to the exact macroscopic dRGT structure.
Domenico Raso (Thu,) studied this question.