We prove in this paper some sharp weighted inequalities for the vector-valued maximal function of Fefferman and Stein defined by ![\begin{displaymath}\overline M_qf(x)=\left(\sum _{i=1}^{\infty}(Mf_i(x))^{q}\right)^{1/q},\end{displaymath}](http://www.ams.org/tran/2000-352-07/S0002-9947-99-02573-8/gif-abstract/img4.gif)
where is the Hardy-Littlewood maximal function. As a consequence we derive the main result establishing that in the range there exists a constant such that ![\begin{displaymath}\int _{\mathbf{R}^{n}}\overline M_qf(x)^p\, w(x)dx\le C\, \int _{\mathbf{R}^n}|f(x)|^{p}_{q}\, M^{\frac pq]+1}w(x) dx.\end{displaymath}](http://www.ams.org/tran/2000-352-07/S0002-9947-99-02573-8/gif-abstract/img8.gif)
Furthermore the result is sharp since cannot be replaced by . We also show the following endpoint estimate ![\begin{displaymath}w(\{x\in \mathbf{R}^n:\overline M_qf(x)>\lambda\})\,\le \frac C\lambda \int _{\mathbf{R}^n} |f(x)|_q\, Mw(x)dx,\end{displaymath}](http://www.ams.org/tran/2000-352-07/S0002-9947-99-02573-8/gif-abstract/img11.gif)
where is a constant independent of . |