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Random polynomials having few or no real zeros
Authors:Amir Dembo   Bjorn Poonen   Qi-Man Shao   Ofer Zeitouni
Affiliation:Department of Mathematics & Statistics, Stanford University, Stanford, California 94305 ; Department of Mathematics, University of California, Berkeley, California 94720-3840 ; Department of Mathematics, University of Oregon, Eugene, Oregon 97403 ; Department of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel
Abstract:Consider a polynomial of large degree $n$whose coefficients are independent, identically distributed, nondegenerate random variables having zero mean and finite moments of all orders. We show that such a polynomial has exactly $k$ real zeros with probability $n^{-b+o(1)}$ as $n rightarrow infty$through integers of the same parity as the fixed integer $k ge 0$. In particular, the probability that a random polynomial of large even degree $n$ has no real zeros is $n^{-b+o(1)}$. The finite, positive constant $b$is characterized via the centered, stationary Gaussian process of correlation function ${mathrm{sech}} (t/2)$. The value of $b$ depends neither on $k$ nor upon the specific law of the coefficients. Under an extra smoothness assumption about the law of the coefficients, with probability $n^{-b+o(1)}$ one may specify also the approximate locations of the $k$ zeros on the real line. The constant $b$ is replaced by $b/2$in case the i.i.d. coefficients have a nonzero mean.

Keywords:Random polynomials   Gaussian processes
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