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Law of large numbers for the discriminant of random polynomials

Probability 2025-06-17 v1 Classical Analysis and ODEs

Abstract

Let fnf_n be a random polynomial of degree nn, whose coefficients are independent and identically distributed random variables with mean-zero and variance one. Let Δ(fn)\Delta(f_n) denote the discriminant of fnf_n, that is Δ(fn)=A2n2i<j(αjαi)2\Delta(f_n) = A^{2n-2}\prod_{i < j} (\alpha_j - \alpha_i)^2 where AA is the leading coefficient of fnf_n and α1,αn\alpha_1,\ldots\alpha_n are its roots. We prove that with high probability Δ(fn)=n2neDn(1+o(1))|\Delta(f_n)| = n^{2n} e^{-{\sf D}_\ast n(1+o(1))} as nn\to \infty, for some explicit universal constant D>0{\sf D}_\ast>0. A key step in the proof is an analytic representation for the logarithm of the discriminant, which captures both the distributional reciprocal symmetry of the random roots and the cancellations this symmetry induces.

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Cite

@article{arxiv.2506.12206,
  title  = {Law of large numbers for the discriminant of random polynomials},
  author = {Marcus Michelen and Oren Yakir},
  journal= {arXiv preprint arXiv:2506.12206},
  year   = {2025}
}

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35 pages