Abstract
Let Q(X) be any integral primitive positive definite quadratic form in k variables, where \({k\geq4}\), and discriminant D. For any integer n, we give an upper bound on the number of integral solutions of Q(X) = n in terms of n, k, and D. As a corollary, we prove a conjecture of Lester and Rudnick on the small scale equidistribution of almost all functions belonging to any orthonormal basis of a given eigenspace of the Laplacian on the flat torus \({\mathbb{T}^d}\) for \({d\geq 5}\). This conjecture is motivated by the work of Berry [2,3] on the semiclassical eigenfunction hypothesis.
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T. Sardari, N. Quadratic Forms and Semiclassical Eigenfunction Hypothesis for Flat Tori. Commun. Math. Phys. 358, 895–917 (2018). https://doi.org/10.1007/s00220-017-3044-1
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DOI: https://doi.org/10.1007/s00220-017-3044-1