On sectoriality of degenerate elliptic operators

Let $c_{kl} \in W^{1,\infty}(Ω, \mathbb{C})$ for all $k,l \in \{1, \ldots, d\}$ and $Ω\subset \mathbb{R}^d$ be open with Lipschitz boundary. We consider the divergence form operator $A_p = - \sum_{k,l=1}^d \partial_l (c_{kl} \, \partial_k)$ in $L_p(Ω)$ when the coefficient matrix satisfies $(C(x) \, ξ, ξ) \in Σ_θ$ for all $x \in Ω$ and $ξ\in \mathbb{C}^d$, where $Σ_θ$ be the sector with vertex 0 and semi-angle $θ$ in the complex plane. We show that a sectorial estimate hold for $A_p$ for all $p$ in a suitable range. We then apply these estimates to prove that the closure of $-A_p$ generates a holomorphic semigroup under further assumptions on the coefficients. The contractivity and consistency properties of these holomorphic semigroups are also considered.

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