Polynomial bounds for eigenfunctions and eigenvalues on random covers of hyperbolic surfaces

Abstract

Let $X$ be a compact connected orientable hyperbolic surface and let $X_n$ be a degree $n$ cover, taken uniformly at random. We show that, with high probability, the $L^\infty$ norm of every Laplace eigenfunction on $X_n$ with bounded eigenvalue decays polynomially in $n$. This gives a polynomial decay analogue of the logarithmic bound of Gilmore--Le Masson--Sahlsten--Thomas [arXiv:1912.09961] in the Weil--Petersson model. Using similar methods, we also show that, with high probability, the distribution of eigenvalues of the Laplacian on $X_n$ converges to the spectral measure of the hyperbolic plane with polynomially decaying error. Our proof relies on the Selberg pre-trace formula and a variant of the polynomial method.