MULTI-PARAMETER EXTENSIONS OF A THEOREM OF PICHORIDES

Extending work of Pichorides and Zygmund to the d-dimensional setting, we show that the supremum of L-p-norms of the Littlewood-Paley square function over the unit ball of the analytic Hardy spaces H-A(p) (T-d) blows up like (p-1)(-d) as p -> 1(+). Furthermore, we obtain an Llog(d) L-estimate for square functions on H-A(1) (T-d). Euclidean variants of Pichorides' theorem are also obtained.