The Logarithmically Averaged Chowla and Elliott Conjectures for Two-point Correlations

Let λ denote the Liouville function. The Chowla conjecture, in the two-point correlation case, asserts that ∑ n6x λ(a1n + b1)λ(a2n + b2) = o(x) as x→∞, for any fixed natural numbers a1, a2 and nonnegative integer b1, b2 with a1b2−a2b1 6= 0. In this paper we establish the logarithmically averaged version ∑ x/ω(x)<n6x λ(a1n + b1)λ(a2n + b2) n = o(logω(x)) of the Chowla conjecture as x → ∞, where 1 6 ω(x) 6 x is an arbitrary function of x that goes to infinity as x → ∞, thus breaking the ‘parity barrier’ for this problem. Our main tools are the multiplicativity of the Liouville function at small primes, a recent result of Matomäki, Radziwiłł, and the author on the averages of modulated multiplicative functions in short intervals, concentration of measure inequalities, the Hardy–Littlewood circle method combined with a restriction theorem for the primes, and a novel ‘entropy decrement argument’. Most of these ingredients are also available (in principle, at least) for the higher order correlations, with the main missing ingredient being the need to control short sums of multiplicative functions modulated by local nilsequences. Our arguments also extend to more general bounded multiplicative functions than the Liouville function λ, leading to a logarithmically averaged version of the Elliott conjecture in the two-point case. In a subsequent paper we will use this version of the Elliott conjecture to affirmatively settle the Erdős discrepancy problem. 2010 Mathematics Subject Classification: 11N37 c © The Author 2016. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/fmp.2016.6 Downloaded from https://www.cambridge.org/core. IP address: 54.191.40.80, on 16 Aug 2017 at 07:50:01, subject to the Cambridge