Mean square value of exponential sums related to representation of integers as sum of two squares Pavel M. Bleher, Freeman J. Dyson (1994) Acta Arithmetica
Mean square value of exponential sums related to the representation of integers as sums of squares Jens Marklof (2005) Acta Arithmetica
Mean value estimates for exponential sums and L-functions: a spectral theoretic approach. Yoichi Motohashi, Matti Jutila (1995) Journal für die reine und angewandte Mathematik
Mean value estimates for exponential sums with applications to L -functions Matti Jutila (1991) Acta Arithmetica