On the zeros of reciprocal Littlewood polynomials

Abstract

Let $P(z)=\sum_{n=0}^Na_nz^n$ be a Littlewood polynomial of degree $N$, meaning that $a_n\in\{\pm 1\}$. We say that $P$ is reciprocal if $P(z)=z^NP(1/z)$. Borwein, Erd\'elyi and Littmann posed the question of determining the minimum number $Z_{\mathcal{L}}(N)$ of zeros of modulus 1 of a reciprocal Littlewood polynomial $P$ of degree $N$. Several finite lower bounds on $Z_{\mathcal{L}}(N)$ have been obtained in the literature, and it has been conjectured by various authors that $Z_{\mathcal{L}}(N)$ must in fact grow to infinity with $N$. Starting from ideas in recent breakthrough papers of Erd\'elyi and Sahasrabudhe, we are able to confirm this.