Geometric Cancellation of the QCD ¯θ Term from Fixed-Point Moduli Stabilization in Type IIB String Theory

The strong Charge–Parity (CP) problem arises from the extreme smallness of the effective quantum chromodynamics (QCD) topological angle ¯θ. This work demonstrates that ¯θ vanishes identically in a class of Type IIB string compactifications with fixed-point moduli stabilization. The cancellation emerges as a structural consequence of flux quantization, supersymmetric extremization, and modular holomorphy, without invoking Peccei–Quinn symmetries, parameter tuning, or vacuum scanning. All contributions to ¯θ are shown to be fixed by the same flux configuration that stabilizes the K¨ahler modulus at τ⋆ ≃ 220, previously derived from vacuum energy considerations. The axion vacuum expectation value, flux-induced gauge phase, and Yukawa determinant phase are individually derived and cancel exactly. The result establishes the strong CP problem as resolved by internal consistency of the fixed-point vacuum