Multiplicative functions that are close to their mean
HTML articles powered by AMS MathViewer
- by Oleksiy Klurman, Alexander P. Mangerel, Cosmin Pohoata and Joni Teräväinen PDF
- Trans. Amer. Math. Soc. 374 (2021), 7967-7990 Request permission
Abstract:
We introduce a simple sieve-theoretic approach to studying partial sums of multiplicative functions which are close to their mean value. This enables us to obtain various new results as well as strengthen existing results with new proofs.
As a first application, we show that for a multiplicative function $f : \mathbb {N} \rightarrow \{-1,1\},$ \begin{align*} \limsup _{x\to \infty }\Big |\sum _{n\leq x}\mu ^2(n)f(n)\Big |=\infty . \end{align*} This confirms a conjecture of Aymone concerning the discrepancy of square-free supported multiplicative functions.
Secondly, we show that a completely multiplicative function $f : \mathbb {N} \rightarrow \mathbb {C}$ satisfies \begin{align*} \sum _{n\leq x}f(n)=cx+O(1) \end{align*} with $c\neq 0$ if and only if $f(p)=1$ for all but finitely many primes and $|f(p)|<1$ for the remaining primes. This answers a question of Ruzsa.
For the case $c = 0,$ we show, under the additional hypothesis \begin{equation*} \sum _{p }\frac {1-|f(p)|}{p} < \infty , \end{equation*} that $f$ has bounded partial sums if and only if $f(p) = \chi (p)p^{it}$ for some non-principal Dirichlet character $\chi$ modulo $q$ and $t \in \mathbb {R}$ except on a finite set of primes that contains the primes dividing $q$, wherein $|f(p)| < 1.$ This provides progress on another problem of Ruzsa and gives a new and simpler proof of a stronger form of Chudakov’s conjecture.
Along the way we obtain quantitative bounds for the discrepancy of the modified characters improving on the previous work of Borwein, Choi and Coons.
References
- M. Aymone, The Erdős discrepancy problem over the squarefree and cubefree integers, e-prints arXiv:1908.10997, Aug 2019.
- Marco Aymone, A note on multiplicative functions resembling the Möbius function, J. Number Theory 212 (2020), 113–121. MR 4080049, DOI 10.1016/j.jnt.2019.10.025
- Peter Borwein, Stephen K. K. Choi, and Michael Coons, Completely multiplicative functions taking values in $\{-1,1\}$, Trans. Amer. Math. Soc. 362 (2010), no. 12, 6279–6291. MR 2678974, DOI 10.1090/S0002-9947-2010-05235-3
- Pablo Candela, Juanjo Rué, and Oriol Serra, Memorial to Javier Cilleruelo: a problem list, Integers 18 (2018), Paper No. A28, 9. MR 3783887
- N. Chudakov, On the generalized characters, Actes du Congrès International des Mathématiciens (Nice, 1970) Gauthier-Villars, Paris, 1971, pp. p. 487. MR 0563889
- N. G. Tchudakoff, Theory of the characters of number semigroups, J. Indian Math. Soc. (N.S.) 20 (1956), 11–15. MR 83515
- Jean-Marie De Koninck, Imre Kátai, and Bui Minh Phong, Three new conjectures related to the values of arithmetic functions at consecutive integers, Ann. Univ. Sci. Budapest. Sect. Comput. 49 (2019), 425–427. MR 4020828
- P. D. T. A. Elliott, The value distribution of additive arithmetic functions on a line, J. Reine Angew. Math. 642 (2010), 57–108. MR 2658182, DOI 10.1515/CRELLE.2010.037
- V. V. Glazkov, Characters of the multiplicative semigroup of natural numbers, Studies in Number Theory, No. 2 (Russian), Izdat. Saratov. Univ., Saratov, 1968, pp. 3–49 (Russian). MR 0236129
- Leo Goldmakher, Multiplicative mimicry and improvements to the Pólya-Vinogradov inequality, Algebra Number Theory 6 (2012), no. 1, 123–163. MR 2950162, DOI 10.2140/ant.2012.6.123
- G. H. Hardy and J. E. Littlewood, The zeros of Riemann’s zeta-function on the critical line, Math. Z. 10 (1921), no. 3-4, 283–317. MR 1544477, DOI 10.1007/BF01211614
- M. N. Huxley, Large values of Dirichlet polynomials. III, Acta Arith. 26 (1974/75), no. 4, 435–444. MR 379395, DOI 10.4064/aa-26-4-435-444
- Imre Kátai and Bui Minh Phong, On the pairs of completely multiplicative functions satisfying some relation, Acta Sci. Math. (Szeged) 85 (2019), no. 1-2, 139–145. MR 3967880
- Oleksiy Klurman, Correlations of multiplicative functions and applications, Compos. Math. 153 (2017), no. 8, 1622–1657. MR 3705270, DOI 10.1112/S0010437X17007163
- Oleksiy Klurman and Alexander P. Mangerel, Rigidity theorems for multiplicative functions, Math. Ann. 372 (2018), no. 1-2, 651–697. MR 3856825, DOI 10.1007/s00208-018-1724-6
- Oleksiy Klurman and Alexander P. Mangerel, On the orbits of multiplicative pairs, Algebra Number Theory 14 (2020), no. 1, 155–189. MR 4076810, DOI 10.2140/ant.2020.14.155
- Terence Tao, The Erdős discrepancy problem, Discrete Anal. , posted on (2016), Paper No. 1, 29. MR 3533300, DOI 10.19086/da.609
- Terence Tao, The logarithmically averaged Chowla and Elliott conjectures for two-point correlations, Forum Math. Pi 4 (2016), e8, 36. MR 3569059, DOI 10.1017/fmp.2016.6
- Gérald Tenenbaum, Introduction to analytic and probabilistic number theory, 3rd ed., Graduate Studies in Mathematics, vol. 163, American Mathematical Society, Providence, RI, 2015. Translated from the 2008 French edition by Patrick D. F. Ion. MR 3363366, DOI 10.1090/gsm/163
- Gérald Tenenbaum, Fonctions multiplicatives, sommes d’exponentielles, et loi des grands nombres, Indag. Math. (N.S.) 27 (2016), no. 2, 590–600 (French, with English summary). MR 3479174, DOI 10.1016/j.indag.2015.11.007
Additional Information
- Oleksiy Klurman
- Affiliation: Max Planck Institute for Mathematics, Bonn, Germany; and School of Mathematics, University of Bristol, United Kingdom
- MR Author ID: 1066461
- Email: lklurman@gmail.com
- Alexander P. Mangerel
- Affiliation: Centre de Recherches Mathématiques, Université de Montréal, Montréal, Québec, Canada
- MR Author ID: 1141860
- Email: smangerel@gmail.com
- Cosmin Pohoata
- Affiliation: Department of Mathematics, California Institute of Technology, Pasadena, California
- MR Author ID: 829354
- Email: apohoata@caltech.edu
- Joni Teräväinen
- Affiliation: Mathematical Institute, University of Oxford, Oxford, United Kingdom
- Email: joni.teravainen@maths.ox.ac.uk
- Received by editor(s): December 1, 2020
- Received by editor(s) in revised form: February 18, 2021
- Published electronically: August 18, 2021
- Additional Notes: The fourth author was supported by a Titchmarsh Fellowship from the University of Oxford
- © Copyright 2021 American Mathematical Society
- Journal: Trans. Amer. Math. Soc. 374 (2021), 7967-7990
- MSC (2020): Primary 11N37, 11N64
- DOI: https://doi.org/10.1090/tran/8427
- MathSciNet review: 4328688