Lusin cotype characterization of martingale cotype for Schrödinger semigroups

Let {Tt}t>0\{T_t\}_{t>0} be the heat semigroup generated by a Schrödinger operator as above, and let {Pt}t>0\{P_t\}_{t>0} be the Poisson semigroup subordinated to {Tt}t>0\{T_t\}_{t>0}. Let XX be a Banach space, and let qq be the cotype exponent in question. Lusin cotype conjecture. If XX is of Lusin cotype qq relative to {Pt}t>0\{P_t\}_{t>0}, then XX is of martingale cotype qq. The same implication should hold for the heat semigroup {Tt}t>0\{T_t\}_{t>0} itself when the underlying differential operator LL is uniformly elliptic. This extends the known characterization for the Laplacian on Rd\mathbb{R}^d with d3d\geq 3 and a potential satisfying a reverse Hölder inequality; the general Schrödinger-semigroup case remains conjectural.

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Primary source

Quanhua Xu, “Holomorphic functional calculus and vector-valued Littlewood-Paley-Stein theory for semigroups”, arXiv:2105.12175 (2024).

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