Abstract
Let and be the n-th Fourier coefficient associated with the symmetric square L-function . For any , we prove that the mean value of over is for almost all in the sense of Lebesgue measure. Furthermore, it holds for all under the Riemann Hypothesis. Furthermore, we obtain that asymptotic formula for over is for almost all , where is the normalized n-th Fourier coefficient associated with a holomorphic cusp form f for the full modular group.
MSC:
11A41; 11F11; 11F30
1. Introduction
Let k be an even positive integer, f be a holomorphic cusp form of weight k for the full modular group and be the normalized n-th Fourier coefficient of f, i.e.,
If we assume that f is an eigenform of all the Hecke operators, then f can be normalized such that and is real. We define the Hecke L-function associated to f for by
For any prime p and all integers , we have
where are the local parameters of at prime p, satisfying
Then we have
Deligne [1,2] proved Ramanujan–Petersson conjecture, i.e.,
for all , where .
In order to detect the sign changes of , many authors have studied the mean value of and obtained some good results. For example, see [1,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. In addition, the sums of over primes have also been studied. It is known that (see for example Section 5.6 of Iwaniec and Kowalski [23]) there exists a constant such that
The upper bound of (1) may reach , assuming the Riemann Hypothesis. Furthermore, we can establish that
by using the analytic properties of the Rankin–Selberg L-function .
Another interesting question considered by many authors is the mean value of over certain sets of primes. For example, Baier and Zhao [24] studied the distribution of at Piatetski–Shapiro primes by considering estimates of exponential sum involving Hecke eigenvalue. Moreover, they conjectured that, for with some suitable , there exists a constant such that
Furthermore, we can define Piatetski–Shapiro prime twins if are primes and , for any fixed . Balog [25] and Dufner [26] proved that
for almost all in the sense of Lebesgue measure. Furthermore, assuming the Riemann Hypothesis of automorphic L-function is true, they found that (2) holds for all . Furthermore, Zhang and Zhai [27] studied the mean value of over Piatetski–Shapiro prime twins.
Motivated by the above results, we are interested in the distribution of at Piatetski–Shapiro prime twins. For the form f, we know the is an L-function for some automorphic representation, which is often called the symmetric-square lift of f. The n-th Fourier coefficient of satisfies
The symmetric square L-function associated to f is defined by
in the half-plane . Then, for all , is also multiplicative, real and
where . Furthermore, for all primes p, we have
Many authors studied the mean value of . For example, see References [28,29,30,31,32,33,34,35,36]. In this paper, we consider the mean value of Fourier coefficients of symmetric square L-function over Piatetski–Shapiro prime twins and obtain the following results, which imply a result on the distribution of at Piatetski–Shapiro prime twins.
Theorem 1.
For almost all and any , we have
Theorem 2.
Assuming the Riemann Hypothesis of symmetric square L-function is true, (3) holds for all .
Corollary 1.
For almost all , we have
Proof.
The result follows easily from Theorem 1 and (2), if we notice that . ☐
Corollary 2.
Assuming the Riemann Hypothesis of symmetric square L-function is true, (4) holds for all .
Proof.
The result follows from Theorem 2 and (2). ☐
Notation.
Throughout the paper, ε always denotes a sufficiently small positive constant. Let be sufficiently small and depend on ε. We write , or , to mean that . Let be the nontrivial zero of the symmetric square L-function . As usual, is the von Mangoldt function.
2. Auxiliary Lemmas
Lemma 1.
Let η run through a countable set of reals, with arbitrary complex such that is absolutely convergent. Let . Then
Proof.
This lemma is Lemma 1 of Gallagher [37]. ☐
Lemma 2.
Let , where is a sufficiently large real number. The
Proof.
This lemma is Lemma of Lü [33]. ☐
Lemma 3.
For , define
Then we have
and
Proof.
From Lemma 2, we have
This combined with Theorem 1.1, 1.2 of Ye and Zhang [38] and [39] gives this lemma. ☐
Lemma 4.
For any , , we have
Proof.
See, for example, Iwaniec and Kowalski [23]. For convenience of calculation, we reduce the summation range of n from to . The contribution of is , in view of . ☐
Lemma 5.
Let be an L-function of degree k such that Rankin–Selberg convolutions and exist, and the latter has a simple pole at while the former is entire if . Suppose that the ramified primes . There exists an absolute constant such that has no zeros in the region
where is the analytic conductor and .
Proof.
This lemma is Theorem 5.10 of Iwaniec and Kowalski [23]. ☐
Lemma 6.
Let x, , and
we have
Proof.
Note that
where is the width of the zero-free region of the symmetric square L-function in Lemma 5. Using integration by parts and Lemma 3, we obtain
where is fulfilled apart from a fixed number of log-factors,
and
We estimate first. The first and second derivatives of are
and
Then is a concave function as . Let , we have . So we have the following three cases.
Case 1. When . In this case, we have and is monotonically decreasing in . Hence
Case 2. When . In this case, the function takes the extreme value at , which gives
Case 3. When . In this case, we have and is monotonically increasing in . Hence,
Combining all the above cases, we have
Next, we need to estimate . It is easy to see that is linear function in , hence
Lemma 7.
Let , . Let be a constant and
If , we have
If , we have
Proof.
This lemma follows from (13) and (16) of Dufner [26]. ☐
3. Proof of Theorem 2
In this section, we write . Then we have
We split the summation range of q into two parts: and to get
For , there is at most one prime satisfying , hence
if we notice that .
For , by the definition of the von Mangoldt function, we have
The error term of the above formula contributes
Let
By the range of n and Taylor’s formula, we have
and
Then
where the O-term comes from
To get (3), it suffices to prove that
The inequality (17) will be proved from a variant of (17) for short intervals. Let , , we can see that the inequality
implies (17). We use Lemma 4 and get
Taking , then we obtain
where
Under the Riemann Hypothesis, we have
Making the change of variables , we deduce that
Using the Cauchy–Schwarz inequality twice, we get
Making the change of variables , we deduce that the last integral in (22) can be written as
where and
Applying Lemma 1 with and to estimate the integral in (23), we have
4. Proof of Theorem 1
To prove Theorem 1, we need Lemma 6 and Lemma 7. Furthermore, we only need to estimate unconditionally. Note that
where
We consider the following integral mean value of ,
with .
From Lemma 6, we know that the upper bound of S depends on the range of T, so we have the following three cases.
Case 1. When .
In this case, we have and use (9) to get
Note that if we have
Case 2. When .
In case of , we use (9) and get
For convenience, we take and consider a quadratic function .
If , we have and is monotonically decreasing in this interval. Hence,
with . Therefore,
If , we get analogously and
where we choose sufficiently small and use the elementary inequality
Therefore,
In case of , we use (10) and get
so we consider a new quadratic function .
If , we get and
Therefore,
Case 3. When .
Therefore,
Therefore,
Combining all the above cases, we obtain
Inequality (20) gives us
Let and . Then by Tschebytschev’s inequality, we obtain
Author Contributions
Conceptualization, X.H. and X.Y.; Methodology, D.Z.; Software, X.H.; Validation, X.H., X.Y. and D.Z.; Formal Analysis, X.H.; Investigation, X.H.; Resources, X.Y.; Data Curation, D.Z.; Writing—Original Draft Preparation, X.H.; Writing—Review & Editing, X.Y.; Visualization, D.Z.; Supervision, D.Z.; Project Administration, D.Z.; Funding Acquisition, X.Y. and D.Z. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by National Natural Science Foundation of China (Grant No. 11771256 and No. 11801327), and Natural Science Foundation of Shandong Province (Grant No. ZR201709280100).
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Acknowledgments
The author would like to thank the referees for their many useful comments.
Conflicts of Interest
The authors declare no conflict of interest.
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