Zeros of random trigonometric functions

2019–2022

My PhD thesis studied the asymptotic behavior of the number of zeros of random trigonometric functions on a fixed interval — almost surely, in distribution, and on average — with a particular focus on universality: to what extent this behavior depends on the law of the coefficients, their correlations, or the choice of basis functions. Working with dependent stationary Gaussian processes, dependence is encoded through the associated spectral measure, whose nature has a decisive impact on the asymptotics and produces both universal and genuinely non-universal regimes. The analysis combines the Kac–Rice formula with techniques inspired by classical work of Salem and Zygmund, and yields new global universality and non-universality results for the zero sets of random trigonometric polynomials.

A random trigonometric polynomial fn(t) = n−1/2k=1n ak cos(kt) + bk sin(kt) with independent standard Gaussian coefficients (top), its real zeros on [0, 2π] marked in red. As the degree n grows, the mean number of zeros divided by n concentrates on the universal constant 2/√3 ≈ 1.1547 (bottom): each dot is one realization, the solid curve the exact expectation E[𝒩]/n = (2/n)√((n+1)(2n+1)/6).
Institution IRMAR, University of Rennes
Supervisors Jürgen Angst, Guillaume Poly
Keywords nodal sets random trigonometric polynomials stationary Gaussian processes spectral measures Kac–Rice formula

Publications

  1. To appear J. Angst, T. Pautrel, G. Poly Global universality of the expected number of zeros of non-analytic random signals INdAM–Springer Proceedings (2025)
  2. Published J. Angst, T. Pautrel, G. Poly Real zeros of random trigonometric polynomials with dependent coefficients Trans. Amer. Math. Soc. 375 (2022), 7209–7260. journal page
  3. Published T. Pautrel New asymptotics for the mean number of zeros of random trigonometric polynomials with strongly dependent Gaussian coefficients Electron. Commun. Probab. 25 (2020), no. 36. journal page

Invited speaker at the "UniRandom" thematic week (Rennes, 2019 and 2021). Slides.