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Bounded Exponential Sums with Multiplicative Coefficients

2025/06/15 by Pierre-Alexandre Bazin, Pylaiev, Ihor, Ihor Pylaiev +2 · 1 citation
Mathematics · #math.NT

paper · pdf · doi:10.48550/arxiv.2506.12845

Abstract

We investigate when the exponential sum Sf(x,α) := ∑n≤ xf(n)e(nα) is bounded, for a multiplicative function f and α∈ℝ. We show that under natural assumptions, Sf(x,α) is bounded only when f is very close to a twisted Dirichlet character χ(n)nit. We obtain sharper classification results for functions that are completely multiplicative or take only finitely many values, including a complete classification in the case when f is completely multiplicative and α is irrational. We also prove a stronger classification under the assumption that the sum is bounded for a positive measure set of α.

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