Bounds for eigenforms on arithmetic hyperbolic 3-manifolds
  On a family of arithmetic hyperbolic 3-manifolds of squarefree level, we prove an upper bound for the sup-norm of Hecke-Maass cusp forms, with a power saving over the local geometric bound simultaneously in the Laplacian eigenvalue and the volume. By a novel combination of diophantine and geometric arguments in a noncommutative setting, we obtain bounds as strong as the best corresponding results on arithmetic surfaces. 
Valentin Blomer, Gergely Harcos, Djordje Mili\'cevi\'c
math.NT