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arXiv · 2511.08445

Non-abelian amplification and bilinear forms with Kloosterman sums

Alexandru Pascadi
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Abstract

We introduce a new method to bound bilinear (Type II) sums of Kloosterman sums with composite moduli $c$, using Fourier analysis on $\mathrm{SL}_2(\mathbb{Z}/c\mathbb{Z})$ and an amplification argument with non-abelian characters. For sums of length $\sqrt{c}$, our method produces a non-trivial bound for all moduli except near-primes, saving $c^{-1/12}$ for products of two primes of the same size. Combining this with previous results for prime moduli, we achieve savings beyond the P\'olya-Vinogradov range for all moduli. We give applications to moments of twisted cuspidal $L$-functions, and to large sieve inequalities for exceptional cusp forms with composite levels.

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Alexandru Pascadi. 2025-11-11. Non-abelian amplification and bilinear forms with Kloosterman sums. https://arxiv.org/abs/2511.08445

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