Growth of Bianchi modular forms

In this talk, I will establish a sharp bound on the growth of cuspidal Bianchi modular forms. By the Eichler-Shimura isomorphism, we actually give a sharp bound of the second cohomology of a hyperbolic three manifold (Bianchi manifold) with local system arising from the representation $Sym^k \otimes \overline{Sym^k}$ of $SL_2(\mathbb{C})$. I will explain how a $p$-adic algebraic method is used for deriving our result.