Cross-Spectral Witness for Hidden Nonequilibrium Beyond the Scalar Ceiling

• URL: http://arxiv.org/abs/2604.03775v3
• Date: Mon, 13 Apr 2026 07:48:10 GMT
• Title: Cross-Spectral Witness for Hidden Nonequilibrium Beyond the Scalar Ceiling
• Abstract summary: coarse graining may absorb hidden forcing into an apparently equilibrium-like reduced description.<n>For scalar observables of linear systems, no time-irreversibility statistic can detect the underlying drive.<n>Within general CSM this certifies shared hidden-sector drive.
• Score: 18.923595971721344
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Partial observation is a pervasive obstacle in nonequilibrium physics: coarse graining may absorb hidden forcing into an apparently equilibrium-like reduced description, so a driven system can look reversible through the only variables one can measure. For scalar Gaussian observables of linear stochastic systems, no time-irreversibility statistic can detect the underlying drive. The Lucente--Crisanti ceiling constrains what one channel carries; what two channels carry is a different question, with a sharp closed-form answer. Two simultaneously observed channels retain an off-diagonal cross-spectral sector inaccessible to any scalar reduction; under channel-separable multiplicative structure the observed-channel response factors cancel identically, leaving a closed-form cross-spectral witness controlled only by the hidden spectrum, the loadings, and the innovation scales, strictly positive at every nonzero cross-coupling including at exact timescale coalescence where every scalar reduction is blind. Within general CSM this certifies shared hidden-sector drive; under the additional one-way coupling assumption the witness identifies the total entropy production rate at leading order with a square-root scaling.

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