Charles University in Prague, Faculty of Mathematics and Physics
Abstract
summary:We characterize the class of weights, invariant under dilations, for which a modified fractional integral operator Iα maps weak weighted Orlicz−ϕ spaces into appropriate weighted versions of the spaces BMOψ, where ψ(t)=tα/nϕ−1(1/t). This generalizes known results about boundedness of Iα from weak Lp into Lipschitz spaces for p>n/α and from weak Ln/α into BMO. It turns out that the class of weights corresponding to Iα acting on weak−Lϕ for ϕ of lower type equal or greater than n/α, is the same as the one solving the problem for weak−Lp with p the lower index of Orlicz-Maligranda of ϕ, namely ωp′ belongs to the A1 class of Muckenhoupt