Sharp Bell–CHSH Bounds Under Total-Variation Measurement Dependence

This work derives an exact and operational tradeoff between Bell–CHSH violation and measurement dependence in local hidden-variable models. Measurement independence is relaxed via a single parameter MMM, defined as the maximum total-variation distance between hidden-variable distributions conditioned on different setting pairs. Under locality, we prove the sharp inequality ∣S∣≤min⁡(2+6M,4)|S| \le \min(2 + 6M, 4)∣S∣≤min(2+6M,4), valid for all admissible MMM, and construct an explicit two-state local model saturating the bound for every M∈[0,1/3]M \in [0, 1/3]M∈[0,1/3]. The result is invertible: any observed CHSH value ∣S∣=2+Δ|S| = 2 + \Delta∣S∣=2+Δ certifies a minimum required measurement dependence M≥Δ/6M \ge \Delta/6M≥Δ/6. The parameter MMM has a direct hypothesis-testing interpretation, placing Bell violations and setting predictability in the same operational units used in statistical distinguishability and cryptography. The paper also provides a linear-programming template that reproduces the analytic frontier and can be adapted to other Bell functionals.