We prove an upper bound for the L4-norm and for the L2-norm restricted to the vertical geodesic of a holomorphic Hecke cusp form f of large weight k. The method is based on Watson's formula and estimating a mean value of certain L-functions of degree 6. Further applications to restriction problems of Siegel modular forms and subconvexity bounds of degree 8 L-functions are given. 2013.
