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arXiv · 2606.23037

Two-mode stability for multi-marginal optimal transport maps

Bang-Xian Han·Zhuo-Nan Zhu
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Abstract

We establish a two-mode stability theory for Monge solutions of the multi-marginal optimal transport problem with barycentric quadratic cost. The associated tuple of maps splits into an external barycentric mode and internal relative modes. A quadratic lower bound for the Kantorovich defect controls the internal modes and yields a square-root estimate without invoking any two-marginal map-stability theorem. The external mode is the optimal transport map from the fixed source to the Wasserstein barycenter. Combining the resulting two-mode estimate with M\'erigot's sharp theorem gives a $\frac{1}{4}$-H\"older estimate for general perturbations, while barycenter-preserving perturbations satisfy a $\frac{1}{2}$-H\"older estimate. We prove that both exponents and the dependence on the weights are optimal. We also examine the scope of such decomposition beyond the barycentric cost: collective-coordinate perturbations and uniformly concave costs of the sum retain the two-mode estimate, whereas the analyses of graph interactions, hedonic costs, and translation-invariant costs identify the two possible obstructions -- loss of relative coercivity and lack of stability for the remaining external modes.

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Bang-Xian Han, Zhuo-Nan Zhu. 2026-06-22. Two-mode stability for multi-marginal optimal transport maps. https://arxiv.org/abs/2606.23037

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