Hybrid Bounds For Automorphic Forms On Ellipsoids Over Number Fields

We prove upper bounds for Hecke-Laplace eigenfunctions on certain Riemannian manifolds X of arithmetic type, uniformly in the eigenvalue and the volume of the manifold. The manifolds under consideration are d-fold products of 2-spheres or 3-spheres, realized as adelic quotients of quaternion algebras over totally real number fields. In the volume aspect we prove a ('Weyl-type') saving of vol (X)(-1/6+epsilon).