The kernel of $Burau(4) \otimes Z_p$ is all pseudo-Anosov
  We show that the kernel of $Burau(4) \otimes Z_p$, the reduced Burau representation with coefficients in $Z_p$ of the 4-braid group $B_4$, consists only of pseudo-Anosov braids. 
Sang Jin Lee, Won Taek Song