Proportionality conjecture for regular Cantor boundaries

Let n=2n=2. Let Ω\Omega be a one-sided NTA domain, and let uu and vv be as above, with u/vu/v agreeing on B(z,r)ΩB(z,r)\cap\partial\Omega with a real-analytic function RR. Assume R=AR=|A| for a nonconstant holomorphic function AA on B(z,r)B(z,r). In addition, suppose that Ω\partial\Omega is a regular Cantor set: there are a>1a>1, δ>0\delta>0, and CC such that for every kZ+k\in\mathbb Z_+, the aka^{-k}-neighborhood of Ω\partial\Omega is a union V1VmkV_1\cup\cdots\cup V_{m_k} with length(Vi)Cak\operatorname{length}(V_i)\leq Ca^{-k} and mkCaδkm_k\leq Ca^{\delta k}. Proportionality conjecture. Then u=λvu=\lambda v for some constant λ\lambda. The claim expresses that a Cantor boundary cannot have the real-analytic alternative from the preceding conjecture; no proof or resolution is supplied here.

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Primary source

Alexander Volberg, “One phase problem for two positive harmonic function: below the codimension 1 threshold”, arXiv:2205.03687 (2022).

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