1. Introduction
The Riemann Hypothesis
is one of the most important unsolved problems in mathematics. Although many efforts and achievements have been made towards proving this celebrated hypothesis, it still remains an open problem
. The Riemann zeta function is originally defined in the half-plane
by the absolutely convergent series
The connection between the above-defined Riemann zeta function and prime numbers was discovered by Euler, i.e., the famous Euler product
where
p runs over the prime numbers.
Riemann showed in his paper in 1859 how to extend the zeta function to the whole complex plane
by analytic continuation, i.e.
where
is the symbol adopted by Riemann to represent the contour integral from
to
around a domain which includes the value 0 but no other point of discontinuity of the integrand in its interior.
Or equivalently,
where
is the Jaccobi theta function,
is the Gamma function in the following Weierstrass expression
where
is the Euler-Mascheroni constant.
As shown by Riemann,
extends to
as a meromorphic function with only a simple pole at
, with residue 1, and satisfies the following functional equation
The Riemann zeta function has zeros at the negative even integers: , , , , ⋯ and one refers to them as the trivial zeros. The other zeros of are the complex numbers, i.e., non-trivial zeros.
In 1896, Hadamard and Poussin independently proved that no zeros could lie on the line , together with the functional equation and the fact that there are no zeros with real part greater than 1, this showed that all non-trivial zeros must lie in the interior of the critical strip. Later on, Hardy (1914) , Hardy and Littlewood (1921) showed that there are infinitely many zeros on the critical line.
To give a summary of the related research on the RH, we have the following results on the properties of the non-trivial zeros of .
Lemma 1: Non-trivial zeroes of , noted as , have the following properties
(1) The number of non-trivial zeroes is infinity;
(2) ;
(3) ;
(4) are all non-trivial zeroes.
As further study, a completed zeta function
is defined as
It is well-known that
is an entire function of order 1. This implies
is analytic, and can be expressed as infinite polynomial, in the whole complex plane
. In addition, replacing
s with
in Equation(6), and combining Equation(5), we obtain the following functional equation
Considering the definition of , and recalling Equation(4), the trivial zeros of are canceled by the poles of . The zero of and the pole of cancel; the zero and the pole of cancel . Thus, all the zeros of are exactly the nontrivial zeros of . Then we have the following Lemma 2.
Lemma 2: The zeros of coincide with the non-trivial zeros of .
Accordingly, the following two statements of the RH are equivalent.
Statement 1: All the non-trivial zeros of have real part equal to .
Statement 2: All the zeros of have real part equal to .
To prove the RH, a natural thinking is to estimate the numbers of non-trivial zeros of inside or outside some certain areas according to Argument Principle. Along this train of thought, there are many research works. Let denote the number of non-trivial zeros of inside the rectangle: , and let denote the number of non-trivial zeros of on the line . Selberg proved that there exist positive constants c and , such that , later on, Levinson proved that , Lou and Yao proved that , Conrey proved that , Bui, Conrey and Young proved that , Feng proved that , Wu proved that .
On the other hand, many non-trivial zeros have been calculated by hand or by computer programs. Among others, Riemann found the first three non-trivial zeros . Gram found the first 15 zeros based on Euler-Maclaurin summation . Titchmarsh calculated the 138th to 195th zeros using the Riemann-Siegel formula . Here are the first three (pairs of) non-trivial zeros: .
The idea of this paper is originated from Euler’s work on proving the following famous equality
This interesting result is deduced by comparing the like terms of two types of infinite expressions, i.e., infinite polynomial and infinite product, as shown in the following
Then the author of this paper conjectured that should be factored into or something like that, which was verified by paring and in the Hadamard product of , i.e.
The Hadamard product of
as shown in Equation(10) was first proposed by Riemann, however, it was Hadamard who showed the validity of this infinite product expansion
.
where
,
runs over all the zeros of the completed zeta function
.
Hadamard pointed out that to ensure the absolute convergence of the infinite product expansion,
and
are paired. Later in
Section 3, we will show that
and
can also be paired to ensure the absolute convergence of the infinite product expansion.
2. Lemmas
In this section, we first explain the concept of the real multiplicity of a zero of . And then we give four lemmas (Lemma 3 to Lemma 6) to support the proof of the RH, among which Lemma 3 is the key lemma.
Multiple zeros of and their real multiplicities: As shown in
Figure 1, the multiple zeros of
are defined in terms of the quadruplet, i.e.,
.
Figure 1.
Illustration of the multiple zeros of .
Figure 1.
Illustration of the multiple zeros of .
There are two different expressions of factors of
for the multiple zeros in
Figure 1, respectively, i.e.,
, or
with
.
To exclude the latter expression, we stipulate that zero
related factors of
take the unique form of
, where
is the real multiplicity of
, here "real" means unique and unchangeable. In
Figure 1, the multiplicity of
is 2, i.e.,
.
Remark: Although the real multiplicity of zero is unknown, it is an objective existence, unique, and unchangeable. This is the key point in the proofs of Lemma 3, Lemma 4, and Lemma 5.
Lemma 3: Given two absolutely convergent infinite products
and
where
s is a complex variable,
and
are the complex conjugate zeros of
,
and
are real numbers,
is the
real multiplicity of
,
.
Then we have
where
is the equivalent sign.
Proof: First of all, we have the following fact:
where
is an integer,
and
are real numbers.
Next, the proof is based on Transfinite Induction.
According to Equation(14),
is an obvious fact as the
Base Case, i.e.,
To be more convincing, let’s further check
, i.e.,
which is also an obvious fact according to Lemma 4.
As the Successor Case, we need to prove .
Thus the Successor Case is true, i.e., .
Next, we prove that holds, by considering well-ordered ordinal set A indexing the family of statements , with the ordering that for all natural numbers n, is the first limit ordinal.
It is well-known that .
To prove that holds, it suffices to prove the Limit Case, i.e., .
Based on Equation(14), it is an obvious fact that
Then we only need to prove, under condition
, that
For the sake of contradiction, assume
under condition
, i.e.
then we have
[Otherwise, since
are absolutely convergent, then through rearrangement of the order of factors in the left-hand part of Equation(19c), we have
, and
(at least
). Further, based on Equation(14), canceling the corresponding factors of these
in the left-hand part of Equation(19c), we obtain
Taking Equation(19b) into consideration, Equation(19d) leads to , this together with , is a contradiction to the assumption Equation(19a).]
Next, we shall show that Equation(19c) contradicts the "divisibility" implied in
It follows from Equation(19e) that
where
is the "divisible" sign.
According to Lemma 6, Equation(19f) implies that either divides (this leads to the violation of the real multiplicities of zeros, similar to the situation in the proofs of Lemma 4 and Lemma 5) or divides (this is impossible, because ). Then we come to an absurdity that .
Thus, assumption Equation(19a) does not hold under condition .
Consequently, Equation(19) holds under condition .
To keep the real multiplicities of zeros unchanged, the imaginary parts should be further limited to .
Thus, the Limit Case is true, i.e., .
Hence, we conclude by Transfinite Induction that
holds, i.e.,
i.e.,
That completes the proof of Lemma 3.
Lemma 4: Given
where
s is a complex variable,
are real numbers,
,
and
are the real multiplicities of
and
, respectively.
Proof: Equation(22) has an obvious solution, i.e.,
Next, we shall show that the above obvious solution is the only solution to Equation(22). Then let us try to find other solutions of Equation(22) by considering
where "gcd" stands for: greatest common divisor.
Based on Equation(22), and suppose
without loss of generality, we have
where
is the "divisible" sign.
By Lemma 6 and Equation(25), it follows that
By comparing like terms of both sides of Equation(28), it follows that
. Consequently,
is a duplicate of
in terms of quadruplet, which is the same situation as shown in
Figure 1. That contradicts the definition of real multiplicities in Equation(22), i.e., in Equation(22) the real multiplicity of
is
, if
, then the real multiplicity of
would be
.
Therefore, the obvious solution Equation(24) is the only solution of Equation(22), i.e.
Further excluding the situation that violates the definition of the real multiplicities of zeros in Equation(29), i.e., , then we know that Equation(23) holds.
That completes the proof of Lemma 4.
Another Proof of Lemma 4: It is obvious that each factor in Equation(22) may divide other two factors on the opposite side. Consequently, Equation(22) can be rewritten as follows
or (suppose
without loss of generality)
k and are constants, which can be easily determined as by comparing the like terms of related polynomial equations. Then, Equation(30) is equivalent to , but Equation(31) yields solution: , which contradicts the definition of the real multiplicities of zeros. After discarding Equation(31), and further excluding the potential situation in the solution of Equation(30), we know that Equation(23) holds.
That completes the proof of Lemma 4.
Lemma 5: Given
where
s is a complex variable,
and
are real numbers,
,
is the real multiplicity of
.
Proof: Equation(32) is equivalent to
Similar to "Another proof of Lemma 4", Equation(34) can be rewritten as follows
or (suppose
without loss of generality)
Then after Equation(36) is abandoned (for that will generate solutions violating the definition of the real multiplicities of zeros) and further excluding the potential situations: , in the solution of Equation(35), we know that Equation(33) holds.
That completes the proof of Lemma 5.
Lemma 6: Let
F be a field,
. If
divides the product
, but
and
are relatively prime, i.e.,
, then
divides
, where
is defined as the set of all polynomials in
x over
F:
Remark: The set equipped with the operations + and · is the polynomial ring in x over the field F.
Remark: The content of Lemma 6 (Polynomial Algebra over Fields) can be found in many textbooks of Linear Algebra or Advanced Algebra. It is the foundation to find other possible solutions in addition to the obvious solution in Lemma 4 and Lemma 5.
3. A Proof of the RH
This section is planned to present a proof of the Riemann Hypothesis. We first prove that Statement 2 of the RH is true, and then by Lemma 2, Statement 1 of the RH is also true. To be brief, to prove the Riemann Hypothesis, it suffices to show that in the new expression of as shown in Equation(37).
Proof of the RH: The details are delivered in three steps as follows.
Step 1:
It is well-known that all the zeros of
always come in complex conjugate pairs. Then by pairing
and
in the Hadamard product as shown in Equation(10), we have
where
.
The absolute convergence of the infinite product in Equation(37) in the form
depends on the convergence of infinite series
, which is an obvious fact according to Theorem 2 in
Section 2, Chapter IV of Ref.[23].
Further, considering the absolute convergence of
we have the following new expression of
by putting all the
related multiple factors (zeros) together in the above Equation(39)
where
is the real multiplicity of
,
.
Step 2: Replacing
s with
in Equation(40), we obtain the infinite product expression of
, i.e.,
Step 3: According to the functional equation
, and considering Equation(40) and Equation(41), we have
which is equivalent to
where
are in order of increasing
, i.e.,
.
To check the absolute convergence of both sides of Equation(43), it suffices to make a comparison with Equation(38) without considering multiple zeros in Equation (
43), i.e., to make a comparison between
and
. It is well-known that the absolute convergence of
depends on the convergence of infinite series
(already proved in Step 1); the absolute convergence of
depends on the convergence of infinite series
, which is also an obvious fact because
, that means
and
have the same convergence.
Then, according to Lemma 3, Equation(43) is equivalent to
Thus, we conclude that all the zeros of the completed zeta function have real part equal to , i.e., Statement 2 of the RH is true. According to Lemma 2, Statement 1 of the RH is also true, i.e., all the non-trivial zeros of the Riemann zeta function have real part equal to .
That completes the proof of the RH.
4. Retrospection and Discussion
On the Simultaneous Zeros of
According to Lemma 1, there are two pairs of complex zeros of simultaneously, i.e., . With the proof of the RH, these 2 pairs of zeros are actually only one pair, because . Thus Lemma 1 could be modified more precisely as follows.
Lemma 1*: Non-trivial zeroes of , noted as , have the following properties
(1) The number of non-trivial zeroes is infinity;
(2) ;
(3) ;
(4) are all non-trivial zeroes.
On the Paring of Zeros of
Hadamard pointed out that to ensure the absolute convergence of the Hadamard product, i.e.,
,
and
are paired. In
Section 3, the author proved that
and
can also be paired to ensure the absolute convergence of the Hadamard product. And that the paring of conjugate zeros, i.e.,
and
, is the right way to express the most essential characteristic of
as (infinite) polynomial with real coefficients, whereas
and
are just another pair of conjugate zeros given by
.
5. Conclusion
This paper presents a proof of the RH based on a new expression of
, i.e.,
where
and
are the complex conjugate zeros of
,
and
are real numbers,
,
is the real multiplicity of
.
The proof is conducted according to Transfinite Induction. The first key-point is the paring of conjugate zeros and to get the new expression of . The second key-point is the use of "real multiplicities" of the zeros of . Obviously, the real multiplicity of a zero of is an objective existence, unique, and unchangeable. As a result, the functional equation finally leads to .
Acknowledgments
The author would like to gratefully acknowledge the help received from Dr. Victor Ignatov (Independent Researcher), Prof. Mark Kisin (Harvard University), Prof. Yingmin Jia (Beihang University), Prof. Tianguang Chu (Peking University), Prof. Guangda Hu (Shanghai University), Prof. Jiwei Liu (University of Science and Technology Beijing), and Dr. Shangwu Wang (Beijing 99view Technology Limited), while preparing this article. The author is also grateful to the editors and referees of PNAS for their constructive comments and suggestions. Finally, with this manuscript, the author pays tribute to Bernhard Riemann and other predecessor mathematicians. They are the shining stars in the sky of human civilization. This manuscript has no associated data.
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