Fonctions maximales centr\'ees de Hardy-Littlewood pour les op\'erateurs   de Grushin
  Let $M_G$ denotes the centered Hardy-Littlewood maximal function associated to the Carnot-Carath\'eodory distance or to the pseudo-distance associated to the fundamental solution of the Grushin operator on $\R_x^n \times \R_u$, $\Delta_G = \sum_{i = 1}^n \frac{\partial^2}{\partial x_i^2} + (\sum_{i = 1}^n x_i^2) \frac{\partial^2}{\partial u^2}$. We get $L^p$ ($p > 1$) dimension free estimates for $M_G$. We prove also that there exists a constant $A > 0$ such that $\| M_G \|_{L^1 \longrightarrow L^{1, \infty}} \leq A n$, $\forall n$. 
Hong-Quan Li
math.CA