Boundary regularity for the fractional heat equation

We study the regularity up to the boundary of solutions to fractional heat equation in bounded $C^{1,1}$ domains. More precisely, we consider solutions to $\partial_t u + (-Δ)^s u=0 \textrm{ in }Ω,\ t > 0$, with zero Dirichlet conditions in $\mathbb{R}^n\setminus Ω$ and with initial data $u_0\in L^2(Ω)$. Using the results of the second author and Serra for the elliptic problem, we show that for all $t>0$ we have $u(\cdot, t)\in C^s(\mathbb{R}^n)$ and $u(\cdot, t)/δ^s \in C^{s-ε}(\overlineΩ)$ for any $ε> 0$ and $δ(x) = \textrm{dist}(x,\partialΩ)$. Our regularity results apply not only to the fractional Laplacian but also to more general integro-differential operators, namely those corresponding to stable Lévy processes. As a consequence of our results, we show that solutions to the fractional heat equation satisfy a Pohozaev-type identity for positive times.

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