The curvature criterion for doubling geodesically convex subsets

From papers

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(AΩ0)+m(AΩ1)\hat{\operatorname{m}}(A)=\operatorname{m}(A\cap\Omega_0)+\operatorname{m}(A\cap\Omega_1)

for all ADbl(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

ΔdΩcK(N1)sin(KN1dM)cos(KN1dM)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 dMd_{\partial M} is not reconciled with the preceding X,ΩX,\Omega notation.

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Sources & referencesView supporting material

Primary source

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

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