Functional calculus for semigroup generators via transference

TL;DR

This paper develops a transference-based approach to establish bounded functional calculi for semigroup generators, demonstrating new bounds and characterizations on Hilbert and Banach spaces, including UMD spaces.

Contribution

It introduces a novel transference principle to prove boundedness of functional calculi for semigroup generators, extending results to UMD spaces and characterizing generators via $m$-bounded calculus.

Findings

Bounded calculus for generators with exponential decay functions

Logarithmic growth of calculus bounds as decay parameter approaches zero

Characterization of semigroup generators via $m$-bounded calculus

Abstract

In this article we apply a recently established transference principle in order to obtain the boundedness of certain functional calculi for semigroup generators. In particular, it is proved that if $-A$ generates a $C_0$-semigroup on a Hilbert space, then for each $\tau>0$ the operator $A$ has a bounded calculus for the closed ideal of bounded holomorphic functions on a (sufficiently large) right half-plane that satisfy $f(z)=O(e^{-\tau\textrm{Re}(z)})$ as $|z|\rightarrow \infty$. The bound of this calculus grows at most logarithmically as $\tau\searrow 0$. As a consequence, $f(A)$ is a bounded operator for each holomorphic function $f$ (on a right half-plane) with polynomial decay at $\infty$. Then we show that each semigroup generator has a so-called (strong) $m$-bounded calculus for all $m\in\mathbb{N}$, and that this property characterizes semigroup generators. Similar results are obtained if the underlying Banach space is a UMD space. Upon restriction to so-called $\gamma$-bounded semigroups, the Hilbert space results actually hold in general Banach spaces.