New Variants of Arithmetic Quantum Ergodicity

We establish two new variants of arithmetic quantum ergodicity. The first is for self-dual \(\textrm{GL}_2\) Hecke–Maaß newforms over \(\mathbb {Q}\) as the level and Laplace eigenvalue vary jointly. The second is a nonsplit analogue wherein almost all restrictions of Hilbert (respectively Bianchi) Hecke–Maaß cusp forms to the modular surface dissipate as their Laplace eigenvalues grow.