Zeros of linear combinations of Dirichlet L-functions on the critical line
Date: Mon, Mar 25, 2024
Location: PIMS, University of British Columbia, Zoom, Online
Conference: Analytic Aspects of L-functions and Applications to Number Theory
Subject: Mathematics, Number Theory
Class: Scientific
CRG: L-Functions in Analytic Number Theory
Abstract:
Fix N≥1 and let L1,L2,…,LN be Dirichlet L-functions with distinct, primitive and even Dirichlet characters. We assume that these functions satisfy the same functional equation. Let F(s)∶=c1L1(s)+c2L2(s)+…+cNLN(s) be a linear combination of these functions (cj∈R∗ are distinct). F is known to have two kinds of zeros: trivial ones, and non-trivial zeros which are confined in a vertical strip. We denote the number of non-trivial zeros ρ with I(ρ)≤T by N(T), and we let Nθ(T) be the number of these zeros that are on the critical line. At the end of the 90's, Selberg proved that this linear combination had a positive proportion of zeros on the critical line, by showing that κF∶=liminfT(Nθ(2T)−Nθ(T))/(N(2T)−N(T))≥c/N2 for some c>0. Our goal is to provide an explicit value for c, and also to improve the lower bound above by showing that κF≥2.16×10−6/(NlogN), for any large enough N.