Automorphic Green functions on Hilbert modular surfaces

Johannes J. Buck

Published 2023-04-26Version 1

In this paper, we generalize results of Bruinier on automorphic Green functions on Hilbert modular surfaces to arbitrary ideals. For instance, we compute the Fourier expansion of the unregularized Green functions, use it to regularize them, obtain the Fourier expansion of the regularized Green functions and evaluate integrals of unregularized and regularized Green functions. Furthermore, we investigate their growth behavior at the cusps in the Hirzebruch compactification by computing the precise vanishing orders along the exceptional divisors. This makes the arithmetic Hirzebruch-Zagier theorem from Bruinier, Burgos Gil and K\"uhn more explicit. To this end, we generalize the theory of local Borcherds products. Lastly, we investigate a new decomposition of the Green functions into smooth functions and compute and estimate the Fourier coefficients of those smooth functions. Finally, this is employed to prove the well-definedness and almost everywhere convergence of the generating series of the Green functions and the modularity of its integral.