A Short Account on Sectorial and Bisectorial Operators

We revise some essentials on the functional calculus for (bi)sectorial operators in Hilbert spaces. The relevant examples for us are elliptic systems in divergence form (sectorial operators), which we will introduce in the subsequent Chap. 6 , and their associated first-order formulations (bisectorial operators), which we study in more detail in Chap. 12 . Functional calculus theory will be heavily and freely used in large parts of this book.