Estimates of sums related to the Nyman-Beurling criterion for the Riemann Hypothesis
Helmut Maier, Michael Th. Rassias

TL;DR
This paper provides a sharp estimate for sums involving the Möbius function related to the Nyman-Beurling criterion for the Riemann Hypothesis, utilizing advanced tools from continued fractions and Fourier series.
Contribution
It introduces a novel, highly precise estimate for sums with the Möbius function in the context of the Nyman-Beurling criterion, advancing understanding of the Riemann Hypothesis.
Findings
Estimate is remarkably sharp compared to previous bounds
Utilizes innovative methods from continued fractions and Fourier series
Enhances analytical tools for studying the Möbius function in number theory
Abstract
We give an estimate for sums appearing in the Nyman-Beurling criterion for the Riemann Hypothesis containing the M\"obius function. The estimate is remarkably sharp in comparison to estimates of other sums containing the M\"obius function. The methods intensively use tools from the theory of continued fractions and from the theory of Fourier series.
Peer Reviews
No public reviews on file for this paper yet. If you reviewed it on a platform where reviews are public (OpenReview, ICLR, NeurIPS, ICML), you can paste yours below so the community can read it here.
Videos
No videos yet. Explain this paper in a talk, walkthrough, or lecture? Add one.
Taxonomy
TopicsAdvanced Harmonic Analysis Research · Mathematical Approximation and Integration
Estimates of sums related to the Nyman-Beurling criterion for the Riemann Hypothesis
Helmut Maier and Michael Th. Rassias
Department of Mathematics, University of Ulm, Helmholtzstrasse 18, 89081 Ulm, Germany.
Institute of Mathematics, University of Zurich, CH-8057, Zurich, Switzerland & Institute for Advanced Study, Program in Interdisciplinary Studies, 1 Einstein Dr, Princeton, NJ 08540, USA.
[email protected], [email protected]
Abstract.
We give an estimate for sums appearing in the Nyman-Beurling criterion for the Riemann Hypothesis containing the Möbius function. The estimate is remarkably sharp in comparison to estimates of other sums containing the Möbius function. The methods intensively use tools from the theory of continued fractions and from the theory of Fourier series.
Key words: Riemann Hypothesis, Riemann zeta function, Nyman-Beurling-Báez-Duarte criterion.
2000 Mathematics Subject Classification: 30C15, 11M26, 42A16, 42A20
1. Introduction and statement of result
According to the approach of Nyman-Beurling-Báez-Duarte (see [1], [6]) to the Riemann Hypothesis, the Riemann Hypothesis is true if and only if
[TABLE]
where
[TABLE]
and the infimum is over all Dirichlet polynomials
[TABLE]
of length (see [7]).
Various authors (cf. [1], [2], [9]) have investigated the question, which asymptotics hold for if the Riemann Hypothesis is true.
In [7] the following was shown:
If the Riemann Hypothesis is true and if
[TABLE]
for some , then
[TABLE]
for
[TABLE]
Moreover, it follows from work of Burnol [9] that among all Dirichlet polynomials the infimum in (1.1) is assumed for . It thus is of interest to obtain an unconditional estimate for the integral in (1.1).
If we expand the square in (1.1) we obtain
[TABLE]
The last integral evaluates as
[TABLE]
We have
[TABLE]
where
[TABLE]
is Vasyunin’s sum (see [21]).
It can be shown that
[TABLE]
where , with the cotangent sum
[TABLE]
Ishibashi [11] observed that is related to the value at or of the Estermann zeta function by the functional equation of the imaginary part. Namely
[TABLE]
where for , , we have:
[TABLE]
and .
If , then de la Bretèche and Tenenbaum [8] showed that the convergence of the above series at is equivalent to the convergence of
[TABLE]
where denotes the -th partial quotient of .
The irrational numbers for which this sum converges are called Wilton numbers.
A basic ingredient in the papers [14], [18] have been the representations of Balazard, Martin in their papers [3], [4], of the function
[TABLE]
involving the Gauss transform from the theory of continued fractions as well as from the paper [19], by Marmi, Moussa and Yoccoz.
These concepts and results also play an important role in the present paper. We shall represent them in the next section.
We now describe our result and its relation to the Nyman-Beurling criterion:
From (1.2) and (1.3) we obtain
[TABLE]
We investigate a partial sum, in which is kept fixed, namely (up to a constant depending only on ):
[TABLE]
which coincides with
[TABLE]
( is a suitable interval).
We prove the following result:
Theorem 1.1**.**
Let , , where . Then there is a positive constant depending only on and , such that
[TABLE]
Remark. This is one of the few cases of a remarkably sharp estimate of a sum containing the Möbius function that is better than the trivial estimate by a factor, which is a positive power of the number of the terms.
Corollary 1.2**.**
Let , , fixed, . Then there is depending only on , such that
[TABLE]
where .
Proof.
This follows from Theorem 1.1 by integration by parts. ∎
2. Continued Fractions
In this section we provide some basic facts related to the theory of continued fractions. We also recall facts and results from the paper [4].
Definition 2.1**.**
Let . For we set . For we define recursively
[TABLE]
This definition is also valid for and , whenever . We set
[TABLE]
We have:
Lemma 2.2**.**
For ,
[TABLE]
*the continued fraction expansion of .
For we have*
[TABLE]
*where is the last , for which .
We define the partial quotient of by*
[TABLE]
We have
[TABLE]
[TABLE]
Proof.
(cf. [10], p. 7.) ∎
Definition 2.3**.**
For let
[TABLE]
Then we call the depth of .
Definition 2.4**.**
Let . Then for , we set:
[TABLE]
(by convention ) and
[TABLE]
*so that
Let be a rational number of depth . Then we set:*
[TABLE]
[TABLE]
For we define Wilton’s function by
[TABLE]
for which the series is convergent.
Definition 2.5**.**
*(definitions from Sec. 4.1 of [4])
For let*
[TABLE]
For let
[TABLE]
For let
[TABLE]
For a rational number of depth let
[TABLE]
Lemma 2.6**.**
We have
[TABLE]
Proof.
This is Proposition 33 of [4]. ∎
Definition 2.7**.**
Let
[TABLE]
Lemma 2.8**.**
The series and converge for the same values and we have
[TABLE]
in each point of convergence.
Proof.
This is Proposition 28 of [4]. ∎
Definition 2.9**.**
For , or a rational number with depth , we define
[TABLE]
where and the operator is defined by
[TABLE]
Lemma 2.10**.**
Let be a Wilton number or a rational number. Then we have:
[TABLE]
Proof.
This follows directly from the definition of Wilton’s function . ∎
Lemma 2.11**.**
For , or a rational number with depth we have
[TABLE]
Proof.
This follows from Lemma 2.10 by the same computation as in the proof of Lemma 2.10 in [18], which is valid also for a rational number with depth . ∎
Lemma 2.12**.**
For , or a rational number of depth we have
[TABLE]
Proof.
This is Lemma 2.11 of [18], whose proof is also valid for rational of depth . ∎
Definition 2.13**.**
Let be a measurable subset of . The measure is defined by
[TABLE]
Lemma 2.14**.**
The measure is invariant with respect to the map , i.e.
[TABLE]
for all measurable subsets .
Proof.
This result is well-known. ∎
Lemma 2.15**.**
Let . For , we have
[TABLE]
where
[TABLE]
Proof.
For the proof of this result, due to Marmi, Moussa and Yoccoz [19], see [18] Lemma 2.8, (ii). ∎
Definition 2.16**.**
Let , and . The cell of depth , is the interval with the endpoints and .
Lemma 2.17**.**
In the interior of the cell of depth , the functions are constants for ,
[TABLE]
The endpoints of are
[TABLE]
*For and there is a unique cell of depth that contains .
Within a cell of depth we have the derivatives*
[TABLE]
[TABLE]
Proof.
See [4], sections 2.3 and 2.4. ∎
Lemma 2.18**.**
Let be as in Definition 2.16. Then we have
[TABLE]
Proof.
We compare the measure of cells of depths and . By (2.1) of Lemma 2.16, we know that has the endpoints
[TABLE]
and thus the length
[TABLE]
The cell has the length
[TABLE]
Thus
[TABLE]
From (2.2) we obtain:
[TABLE]
which concludes the proof of Lemma 2.18. ∎
Lemma 2.19**.**
We have
[TABLE]
Proof.
This follows from
[TABLE]
∎
Lemma 2.20**.**
Let be sufficiently large. Then there exists , such that for ,
[TABLE]
Proof.
By partition into cells of depth we obtain from Lemmas 2.18 and 2.19 the following:
[TABLE]
The integral in (2.3) is
[TABLE]
where are i.i.d. exponentially distributed random variables with rate 2. The distribution of the sum is the Gamma distribution with density
[TABLE]
Lemma 2.20 now follows from (2.3) and (2.4). ∎
3. Vaughan’s identity
We now express the Möbius function by Vaughan’s identity.
Lemma 3.1**.**
Let . For we have:
[TABLE]
where
[TABLE]
for
[TABLE]
[TABLE]
and
[TABLE]
Proof.
Cf. [12]. ∎
We now obtain
[TABLE]
where
[TABLE]
From the definitions for and in Lemma 3.1 we obtain:
[TABLE]
where
[TABLE]
We now choose
[TABLE]
depending only on and . The subsequent steps are all valid, if is sufficiently small.
We partition the sum as follows:
[TABLE]
with
[TABLE]
and
[TABLE]
A trivial estimate of the sum gives:
[TABLE]
The sums and are estimated by the same method.
In the next section we shall give the details of the estimate of , whereas the estimate of will be given in the last section.
4. The sums and
We now choose , where depends only on and . In the sequel we shall always assume that is sufficiently small.
For the tuplets appearing in the sum at least one of the two cases must hold:
[TABLE]
[TABLE]
since otherwise we would have the inequalities
[TABLE]
which in turn would lead to the contradiction
[TABLE]
Since the cases 1) and 2) are symmetric, it suffices to treat case 1 only.
We write
[TABLE]
where
[TABLE]
We estimate and trivially by
[TABLE]
[TABLE]
and now describe the estimate of the sums .
We set
[TABLE]
and define and as follows:
Let
[TABLE]
[TABLE]
[TABLE]
We define
[TABLE]
and obtain
[TABLE]
We now make use of the antisymmetry of the function :
[TABLE]
We replace the points
[TABLE]
by the mirror images of the points
[TABLE]
namely by
[TABLE]
and due to (4.1) we obtain
[TABLE]
We have
[TABLE]
We now partition the range of summation over the points in cells of depth and assume that is chosen so small that for all cells of depth with the possible exceptions of cells of depth with total measure for some .
This can be achieved because of Lemma 2.20. Denote the union of these exceptional cells by .
For the points
[TABLE]
we estimate the difference in (4.5) by the trivial bound
[TABLE]
We obtain
[TABLE]
where is extended over all tuplets with
[TABLE]
and
[TABLE]
For the other cells we use that
[TABLE]
and substitute
[TABLE]
This leads to the problem to estimate the differences
[TABLE]
and
[TABLE]
This can be done by appeal to Lemmas 2.6, 2.17 and (4.6). The sum containing the terms can be estimated using Lemma 2.12. We obtain
[TABLE]
By (4.1), (4.2), (4.3) we get:
[TABLE]
By the same method we derive
[TABLE]
[TABLE]
5. The sum
We have
[TABLE]
where
[TABLE]
Therefore
[TABLE]
with
[TABLE]
We observe that
[TABLE]
where denotes the divisor function sum of order .
Let
[TABLE]
We recursively define the sequence of regions that exhaust .
Let be the union of squares with sides parallel to the coordinate axes, the coordinates of whose vertices are integer multiples of and side lengths , that are completely contained in .
The recursion : Assume that has been defined. We let be the union of squares of sides parallel to the coordinate axes of side lengths , the coordinates of their vertices are integer multiples of , whose interiors are contained in the set . We set
[TABLE]
We choose as the minimal , such that
[TABLE]
for all squares of side lengths contained in .
Since the boundaries of are straight lines, the trivial bound (4.7) gives
[TABLE]
Let be a square of and
[TABLE]
We set
[TABLE]
Because of (5.4) we have
[TABLE]
[TABLE]
for sufficiently small.
We now estimate
[TABLE]
By the Cauchy-Schwarz inequality we have:
[TABLE]
We have
[TABLE]
where
[TABLE]
We now make use of the representation
[TABLE]
which follows from Lemmas 2.8 and 2.11.
We set
[TABLE]
and replace by
[TABLE]
by removing the terms , in (5.10).
By Lemmas 2.11 and 2.12 it follows that
[TABLE]
We now partition the sum as follows
[TABLE]
where in the summation is extended over all , for which
[TABLE]
and in the summation is extended over the other values of .
By the definition of , for the appearing in the intervals
[TABLE]
belong to cells resp. of depth as described in Lemma 2.20.
Let be an interval of length 1. By Lemma 2.20 we have
[TABLE]
with the exception of at most
[TABLE]
In we replace the terms by their averages
[TABLE]
The intervals
[TABLE]
are contained in some cells of depth .
We set
[TABLE]
where
[TABLE]
By Lemma 2.20 we have
[TABLE]
We now write
[TABLE]
[TABLE]
and show that is small in average. We have
[TABLE]
We apply Lemma 2.15 for the estimate of
[TABLE]
and obtain by the Cauchy-Schwarz inequality
[TABLE]
In the sum is extended over all squares whose union is .
We replace the integrands in (5.17) by finite partial sums of their Fourier series
[TABLE]
where
[TABLE]
By Parseval’s equation we obtain
[TABLE]
We finally also replace by
[TABLE]
where is extended over the same values as in formula (5.13).
From (5.9), (5.11), (5. 12), (5.13), (5.14), (5.15), (5.16), (5.19) and (5.20) we obtain:
[TABLE]
where
[TABLE]
From the identity
[TABLE]
we obtain
[TABLE]
[TABLE]
6. Conclusion
Theorem 1.1 now follows from (3.1), (3.2), (4.11), (4.12) and (5.22).
The reference list from the paper itself. Each links out to its DOI / PubMed record.
- 1[1] L. Báez-Duarte, M. Balazard, B. Landreau, E. Saias, Notes sur la fonction ζ 𝜁 \zeta de Riemann. III (French) [Notes on the Riemann ζ 𝜁 \zeta -function. III], Adv. Math. 149(2000), no. 1, 130–144.
- 2[2] L. Báez-Duarte, M. Balazard, B. Landreau, E. Saias, Étude de l’autocorrelation multiplicative de la fonction ’partie fractionnaire’ , (French) [Study of the multiplicative autocorrelation of the fractional part function], Ramanujan J., 9(2005), no. 1–2, 215–240; arxiv math.NT/0306251.
- 3[3] M. Balazard, B. Martin, Comportement local moyen de la fonction de Brjuno (French) [Average local behavior of the Brjuno function], Fund. Math., 218(3)(2012), 193–224.
- 4[4] M. Balazard, B. Martin, Sur l’autocorrélation multiplicative de la fonction“partie fractionnaire” et une fonction définie par J. R. Wilton , ar Xiv: 1305.4395 v 1.
- 5[5] S. Bettin, On the distribution of a cotangent sum , Int. Math. Res. Notices (2015), doi: 10.1093/imrn/rnv 036
- 6[6] S. Bettin and B. Conrey, Period functions and cotangent sums , Algebra & Number Theory 7(1)(2013), 215–242.
- 7[7] S. Bettin, J. B. Conrey, D. W. Farmer, An optimal choice of Dirichlet polynomials for the Nyman-Beurling criterion , (in memory of Prof. A. A. Karacuba), ar Xiv:1211.5191
- 8[8] R. de la Bretèche and G. Tenenbaum, Séries trigonométriques à coefficients arithmétiques , J. Anal. Math., 92(2004), 1–79.
