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A Complete Classification of Fourier Summation Formulas on the real line

Classical Analysis and ODEs 2025-04-04 v1 Metric Geometry Number Theory

Abstract

We completely classify Fourier summation formulas of the form Rφ^(t)dμ(t)=n=0a(λn)φ(λn), \int_{\mathbb{R}} \widehat{\varphi}(t) d\mu(t)=\sum_{n=0}^{\infty} a(\lambda_n)\varphi(\lambda_n), that hold for any test function φ\varphi, where φ^\widehat\varphi is the Fourier transform of φ\varphi, μ\mu is a fixed complex measure on R\mathbb{R} and a:{λn}n0Ca:\{\lambda_n\}_{n\geq 0}\to\mathbb{C} is a fixed function. We only assume the decay condition Rdμ(t)(1+t2)c1+n0a(λn)ec2λn<, \int_{\mathbb{R}} \frac{d |\mu|(t)}{(1+t^2)^{c_1}} + \sum_{n\geq 0} |a(\lambda_n)|e^{-c_2 |\lambda_n|}<\infty, for some c1,c2>0c_1,c_2>0. This completes the work initiated by the first author previously, where the condition c11c_1\leq 1 was required. We prove that any such pair (μ,a)(\mu,a) can be uniquely associated with a holomorphic map F(z)F(z) in the upper-half space that is both almost periodic and belongs to a certain higher index Nevanlinna class. The converse is also true: For any such function FF it is possible to generate a Fourier summation pair (μ,a)(\mu,a). We provide important examples of such summation formulas not contemplated by the previous results, such as Selberg's trace formula.

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Cite

@article{arxiv.2504.02741,
  title  = {A Complete Classification of Fourier Summation Formulas on the real line},
  author = {Felipe Gonçalves and Guilherme Vedana},
  journal= {arXiv preprint arXiv:2504.02741},
  year   = {2025}
}

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19 pages