Riesz transforms and conjugacy for Laguerre function expansions of Hermite type

Riesz transforms and conjugate Poisson integrals for multi-dimensional Laguerre function expansions of Hermite type with index α are defined and investigated. It is proved that for any multi-index α = (α1, . . . , αd ) such that αi −1/2, αi /∈ (−1/2, 1/2), the appropriately defined Riesz transforms Rα j , j = 1, 2, . . . , d, are Calderón–Zygmund operators, hence their mapping properties follow from a general theory. Similar mapping results are obtained in one dimension, without excluding α ∈ (−1/2, 1/2), by means of a local Calderón–Zygmund theory and weighted Hardy’s inequalities. The conjugate Poisson integrals are shown to satisfy a system of Cauchy–Riemann type equations and to recover the Riesz–Laguerre transforms on the boundary. The two specific values of α, (−1/2, . . . ,−1/2) and (1/2, . . . , 1/2), are distinguished since then a connection with Riesz transforms for multi-dimensional Hermite function expansions is established. © 2006 Elsevier Inc. All rights reserved