English

Anti-concentration applied to roots of randomized derivatives of polynomials

Probability 2024-07-09 v3

Abstract

Let (Zk(n))1kn(Z^{(n)}_k)_{1 \leq k \leq n} be a random set of points and let μn\mu_n be its \emph{empirical measure}: μn=1nk=1nδZk(n).\mu_n = \frac{1}{n} \sum_{k=1}^n \delta_{Z^{(n)}_k}. Let Pn(z):=(zZ1(n))(zZn(n))andQn(z):=k=1nγk(n)1jn,jk(zZj(n)),P_n(z) := (z - Z^{(n)}_1)\cdots (z - Z^{(n)}_n)\quad \text{and}\quad Q_n (z) := \sum_{k=1}^n \gamma^{(n)}_k \prod_{1 \leq j \leq n, j \neq k} (z- Z^{(n)}_j), where (γk(n))1kn(\gamma^{(n)}_k)_{1 \leq k \leq n} are independent, i.i.d. random variables with Gamma distribution of parameter β/2\beta/2, for some fixed β>0\beta > 0. We prove that in the case where μn\mu_n almost surely tends to μ\mu when nn \rightarrow \infty, the empirical measure of the complex zeros of the \emph{randomized derivative} QnQ_n also converges almost surely to μ\mu when nn tends to infinity. Furthermore, for k=o(n/logn)k = o(n / \log n), we obtain that the zeros of the kk-th \emph{randomized derivative} of PnP_n converge to the limiting measure μ\mu in the same sense. We also derive the same conclusion for a variant of the randomized derivative related to the unit circle.

Keywords

Cite

@article{arxiv.2404.12472,
  title  = {Anti-concentration applied to roots of randomized derivatives of polynomials},
  author = {André Galligo and Joseph Najnudel and Truong Vu},
  journal= {arXiv preprint arXiv:2404.12472},
  year   = {2024}
}

Comments

18 pages, 4 figures