Quantitative QFTCS Calculation of the Doubly Suppressed KRW Divergence in the Helically Identified Kerr Interior

We perform a quantitative quantum field theory in curved spacetime (QFTCS) calculation of ⟨Tµν⟩ren at the inner Cauchy horizon r− of the near-extremal Kerr spacetime with the helical Zn identification of Ref. [1]. Two independent suppression mechanisms for the Kay–Radzikowski–Wald (KRW) divergence [8] are established. Mechanism 1 (primary): the Zn identification restricts scalar, electromagnetic, and gravitational field modes to the diagonal sublattice Dn = {(k, m) : k ≡ m (mod n)} of density 1/n in Z 2 . This gives an exact 1/n suppression of the overall coefficient of the image-sum two-point function on Mfint (exact in the two-point function structure, independent of background curvature), and a leading-order 1/n suppression of Re⟨Tµν⟩ (n) ren with O(β) curvature corrections identified as open computation 1 (Claim ?? of Ref. [4]). This result is non-local by construction: it operates through the global Hadamard two-point function via the method of images and is independent of any local observer property. Mechanism 2 (secondary, conditional): for τ > τthresh = πa( √ 2 − 1), the CTC orbit is radially geodesic, eliminating the per-traversal Unruh thermal amplification that drives the blueshift cascade. The geodesic mechanism suppresses the Unruh component of the divergence and is secondary: Mechanism 1 alone is sufficient for the main conclusion. At n = nmax ∼ a/ℓP for M = 108M⊙, a ≳ 0.99M, Mechanism 1 alone gives horizon destruction timescale tdest ∼ 10300 yr ≫ tHubble. Adding Mechanism 2 (τ > τthresh) further suppresses ⟨Tµν⟩ren to ∼ 6 × 10−117 J m−3 (∼ 10−230 of the Planck energy density), rendering the estimate conservative. We establish three results rigorously and identify two open computations. The Zn identification is imposed on the interior vacuum Mint only; the no-surgery principle [1] ensures the exterior asymptotically flat Kerr metric is unaffected, and the Israel junction conditions at the boundary Σ1 are satisfied exactly. The nmax UV cutoff arises from the Planck-time CTC-orbit condition, not from an ad hoc truncation, and constitutes a physical UV bound whose covariant status is discussed explicitly. The near-extremal (a ≳ 0.99M, not a = M) regime keeps κ− > 0 throughout, so the near-horizon plane-wave approximation is controlled, improving monotonically as a → M− without reaching the degenerate NHEK limit.