Zeros of linear combinations of Dirichlet L-functions on the critical line

Speaker: Jérémy Dousselin

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 N1 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 (cjR 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 κF2.16×106/(NlogN), for any large enough N.