The curvature criterion for doubling geodesically convex subsets

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Let XX be an RCD(K,N)RCD(K,N) space, and let Ω\Omega be a geodesically convex open subset of XX with m⁡(∂Ω)=0\operatorname{m}(\partial\Omega)=0. Let m⁡^\hat{\operatorname{m}} be the measure on Dbl⁡(Ω‾)\operatorname{Dbl}(\overline\Omega) defined by

m⁡^(A)=m⁡(A∩Ω0)+m⁡(A∩Ω1)\hat{\operatorname{m}}(A)=\operatorname{m}(A\cap\Omega_0)+\operatorname{m}(A\cap\Omega_1)

for all A⊂Dbl⁡(Ω‾)A\subset\operatorname{Dbl}(\overline\Omega), where Ω0\Omega_0 and Ω1\Omega_1 are the two copies of Ω\Omega. Doubling curvature criterion. The measured doubled space (Dbl⁡(Ω‾),m⁡^)(\operatorname{Dbl}(\overline\Omega),\hat{\operatorname{m}}) satisfies RCD(K,N)RCD(K,N) if and only if

ΔdΩc≤−K(N−1)sin⁡(KN−1d∂M)cos⁡(KN−1d∂M)on Ω.\Delta d_{\Omega^c}\leq-\sqrt{K(N-1)}\frac{\sin\left(\sqrt{\frac{K}{N-1}}d_{\partial M}\right)}{\cos\left(\sqrt{\frac{K}{N-1}}d_{\partial M}\right)}\quad\text{on }\Omega.

This is formulated as an if-and-only-if conjecture in the supplied candidate, although the surrounding text presents related Riemannian and RCDRCD doubling results; the notation d∂Md_{\partial M} is not reconciled with the preceding X,ΩX,\Omega notation.

References

Primary source

Christian Ketterer, “Glued spaces and lower curvature bounds”, arXiv:2408.13137 (2026).

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