## Revista Matemática Iberoamericana

### Littlewood-Paley-Stein theory for semigroups in UMD spaces

Tuomas P. Hytönen

#### Abstract

The Littlewood-Paley theory for a symmetric diffusion semigroup $T^t$, as developed by Stein, is here generalized to deal with the tensor extensions of these operators on the Bochner spaces $L^p(\mu,X)$, where $X$ is a Banach space. The $g$-functions in this situation are formulated as expectations of vector-valued stochastic integrals with respect to a Brownian motion. A two-sided $g$-function estimate is then shown to be equivalent to the UMD property of $X$. As in the classical context, such estimates are used to prove the boundedness of various operators derived from the semigroup $T^t$, such as the imaginary powers of the generator.

#### Article information

Source
Rev. Mat. Iberoamericana, Volume 23, Number 3 (2007), 973-1009.

Dates
First available in Project Euclid: 27 February 2008

Permanent link to this document
https://projecteuclid.org/euclid.rmi/1204128308

Mathematical Reviews number (MathSciNet)
MR2414500

Zentralblatt MATH identifier
1213.42012

#### Citation

Hytönen, Tuomas P. Littlewood-Paley-Stein theory for semigroups in UMD spaces. Rev. Mat. Iberoamericana 23 (2007), no. 3, 973--1009. https://projecteuclid.org/euclid.rmi/1204128308

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