Mixed weak estimates of Sawyer type for generalized maximal operators

Abstract: We study mixed weak estimates of Sawyer type for maximal operators associated to the family of Young functions $\Phi(t)=t^r(1+\log^+t)^{\delta}$, where $r\geq 1$ and $\delta\geq 0$. More precisely, if $u$ and $v^r$ are $A_1$ weights, and $w$ is defined as $w=1/\Phi(v^{-1})$ then the following estimate [uw\left(\left{x\in \mathbb{R}^n: \frac{M_\Phi(fv)(x)}{v(x)} > t\right}\right) \leq C\int_{\mathbb{R}^n} \Phi\left(\frac{|f(x)|v(x)}{t}\right)u(x) \,dx] holds for every positive $t$. This extends mixed estimates to a wider class of maximal operators, since when we put $r=1$ and $\delta=0$ we recover a previous result for the Hardy-Littlewood maximal operator. This inequality generalizes some previous results proved by Cruz Uribe, Martell and P\'erez in (Int. Math. Res. Not. (30): 1849-1871, 2005). Moreover, it includes estimates for some maximal operators related with commutators of Calder\'on-Zygmund operators.