# Journal of Operator Theory

Volume 71, Issue 1, Winter 2014 pp. 223-257.

Hoermander type functional calculus and square function estimates**Authors**: Christoph Kriegler

**Author institution:**Laboratoire de Mathematiques (CNRS UMR 6620), Universite Blaise-Pascal (Clermont-Ferrand 2), Campus des Cezeaux, 63177 Aubiere Cedex, France

**Summary:**We investigate Hoermander spectral multiplier theorems as they hold on $X = L^p(\Omega), 1 < p < \infty,$ for many self-adjoint elliptic differential operators $A$ including the standard Laplacian on $\R^d.$ A strengthened matricial extension is considered, which coincides with a completely bounded map between operator spaces in the case that $X$ is a Hilbert space. We show that the validity of the matricial H\"ormander theorem can be characterized in terms of square function estimates for imaginary powers $A^{\mathrm it}$, for resolvents $R(\lambda,A),$ and for the analytic semigroup $\exp(-zA).$ We deduce Hoermander spectral multiplier theorems for semigroups satisfying generalized Gaussian estimates.

**DOI:**http://dx.doi.org/10.7900/jot.2012jan23.1956

**Keywords:**functional calculus, square functions, Hoermander spectral multipliers, operator spaces

Contents Full-Text PDF