The $L^p$ regularity problem for parabolic operators with transversally independent coefficients

In this paper, we fully resolve the question of whether the Regularity problem for the parabolic PDE $\partial_tu - \mbox{div}(A\nabla u)=0$ on the domain $\mathbb R^{n+1}_+\times\mathbb R$ is solvable for some $p\in (1,\infty)$ under the assumption that the matrix $A$ is elliptic, has bounded and measurable coefficients and its coefficients are independent of the spatial variable $x_{n+1}$ (which is transversal to the boundary). We prove that for some $p_0>1$ the Regularity problem is solvable in the range $(1,p_0)$. An analogous result for the Dirichlet problem has been considered earlier by Auscher, Egert and Nystr\"om, however the Regularity problem represents an additional step up in difficulty. In the elliptic case, the analog of the question considered here was resolved for both Dirichlet and Regularity problems by Hofmann, Kenig, Mayboroda and Pipher. The main result of this paper complements a recent work of two of the authors with L. Li showing solvability of the parabolic Regularity problem for data in some $L^p$ spaces when the coefficients satisfy a natural Carleson condition (which is a parabolic analog of the so-called DKP-condition).