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An exponential sum involving Fourier coefficients of eigenforms for \(SL(2,\pmb {{\mathbb {Z}}})\)

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Abstract

Let \(\lambda _f (n)\) denote the normalized n-th Fourier coefficient of a holomorphic Hecke eigencuspform or a Hecke–Maass cusp form for the full modular group. In this paper we shall exhibit cancellations in the following sum:

$$\begin{aligned} \sum _{N<n \leqslant 2N} \lambda _f(n) \nu (n) e\left( \alpha n^{\theta }\right) , \end{aligned}$$

where \(\alpha , \ \theta \) are real numbers with \(0< \theta <1\), and \(\nu (n)\) is either \(\mu (n)\) or \(\Lambda (n)\).

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Acknowledgements

The authors would like to thank Satadal Ganguly and Ritabrata Munshi for helpful suggestions and comments. They also thank ISI Kolkata for wonderful academic atmosphere.

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Correspondence to Ratnadeep Acharya.

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During the work, S. Singh was supported by the Department of Atomic Energy, Government of India, NBHM post doctoral fellowship No: 2/40(15)/2016/R&D-II/5765.

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Acharya, R., Singh, S.K. An exponential sum involving Fourier coefficients of eigenforms for \(SL(2,\pmb {{\mathbb {Z}}})\). Ramanujan J 54, 699–716 (2021). https://doi.org/10.1007/s11139-020-00255-0

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  • DOI: https://doi.org/10.1007/s11139-020-00255-0

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