Electron. J. Differential Equations, Vol. 2026 (2026), No. 53, pp. 1-20.

Extrapolation of solvability of the parabolic L^p Neumann problem on bounded Lipschitz cylinders

Martin Dindos, Yingyi Liu

Abstract:
A recent result of the first author with Li and Pipher established the extrapolation of solvability of the \(L^p\) parabolic Neumann problem on unbounded graph domains of the form \(\Omega=\{(x',x_n):x_n>\phi(x')\}\times\mathbb{R}\), where \(\phi:\mathbb{R}^{n-1}\to\mathbb{R}\) is a Lipschitz function. The result shows that under the assumptions that the \(L^p\) parabolic Neumann problem for the equation \(Lu=-\partial_t u+\operatorname{div}(A\nabla u)=0\) in \(\Omega\) and the \(L^{p'}\) parabolic Dirichlet problem for the adjoint equation \(L^*u=\partial_t u+\operatorname{div}(A^T\nabla u)=0\) in \(\Omega\) are solvable, then also the \(L^q\) parabolic Neumann problem for the equation \(Lu=0\) in \(\Omega\) is solvable for all \(1< q< p\).
However, the mentioned paper does not answer the question whether the same claim is also true for domains of the form \(\mathcal O\times\mathbb{R}\), where \(\mathcal O\) is a bounded Lipschitz domain (in spatial variables) since this case does not follow from our argument for the unbounded case. Indeed, the bounded Lipschitz cylinder case requires a significantly different approach which we present in this article and establish an analogous result when \(\mathcal O\) is a bounded Lipschitz domain.

Submitted May 4, 2026. Published July 13, 2026.
Math Subject Classifications: 35K20, 35K10.
Key Words: Parabolic Neumann problem; bounded Lipschitz cylinder; extrapolation of solvability; non-tangential maximal function; atomic Hardy space; parabolic Dirichlet problem.
DOI: 10.58997/ejde.2026.53

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Martin Dindos
School of Mathematics
The University of Edinburgh and
Maxwell Institute of Mathematical Sciences
Edinburgh, UK
email: M.Dindos@ed.ac.uk
Yingyi Liu
School of Informatics
The University of Edinburgh
Edinburgh, UK
email: s2029366@ed.ac.uk

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