- Research
- Open access
- Published:
A sum analogous to the high-dimensional Kloosterman sums and its upper bound estimate
Journal of Inequalities and Applications volume 2013, Article number: 130 (2013)
Abstract
The main purpose of this paper is, using the properties of Gauss sums and the estimate for the generalized exponential sums, to study the upper bound estimate problem of one kind sums analogous to the high-dimensional Kloosterman sums and to give some interesting mean value formula and an upper bound estimate for it.
MSC:11L05.
1 Introduction
For any integer , the high-dimensional Kloosterman sums are defined as follows:
where , denotes the summation over all integers such that , and m are integers with , denotes the solution of the congruent equation ().
There are several results on the properties of the Kloosterman sums . For example, see [1, 2] and [3]. Related works can also be found in [4–8] and [9].
In this paper, we consider a sum analogous to the high-dimensional Kloosterman sums as follows:
where χ is a Dirichlet character modq.
If and (an odd prime), then for any integer a with , applying the Fermat little theorem, one can deduce . So, the sum (1.1) becomes
It is a special case of the general polynomial character sums
where M and N are any positive integers and is a polynomial. Let χ be a q th-order character modp. If is not a perfect q th power modp, then from Weil’s classical work (see [10]), we can deduce the estimate
where ‘≪’ constant depends only on the degree of . Some related results can also be found in [11–13] and [14].
Now we are concerned with the upper bound estimate problem of (1.1). Regarding this contents, it seems that nobody has yet studied it, at least we have not seen any related result before. The problem is interesting because it can reflect some new properties of character sums. The main purpose of this paper is, using the analytic methods and the properties of Gauss sums, to study this problem and give a sharp upper bound estimate for (1.1). That is, we prove the following conclusions.
Theorem 1 Let p be an odd prime, let k be a positive integer with , and let χ be any non-principal character modp. Then for any integers and m with , we have the identity
where denotes the principal character modp.
Theorem 2 Let p be an odd prime, let k be a positive integer with , and let χ be any non-principal character modp. Then for any integers and m with , we have the estimate
Theorem 3 Let p and q be two odd primes, let r be any qth non-residue modp. Then for any integers with , we have the identity
If , then the above formula also holds for , where denotes the Legendre symbol.
Taking and in Theorem 3, note that , we may immediately deduce the following.
Corollary Let p be an odd prime with , then we have the identity
where r and s are any two integers such that .
This gives another proof for a classical work in elementary number theory (i.e., see [15] Theorems 4-11): For any prime p with , there exist two positive integers x and y such that .
2 Several lemmas
To complete the proof of our theorems, we need the following basic lemmas.
Lemma 1 Let p be an odd prime, let χ be any non-principal character modp, and let k be any positive integer such that or . Then for any integer m with , we have the identity
where , denotes the principal character modp, denotes any k-order character modp and .
Proof If , then there exists one integer r with such that . This time, for any integer a with , we have . If a passes through a reduced residue system modp, then also passes through a reduced residue system modp. Therefore, we have
If and with , then there must exist an integer n with such that . For this n, we have
or
Since , from the above identity, we have
If , then χ must be a k th character modp, so there exists one character such that . Let be a k-order character modp (i.e., ), then for any integer a with , note that
From the properties of Gauss sums, we have
Now Lemma 1 follows from (2.1), (2.2) and (2.3). □
Lemma 2 Let p and q be two odd primes with , and let be any q-order character modp. Then for any integers and m with , we have the identities
where denotes the Legendre symbol, and .
Proof If q is an odd prime, then and , so applying (2.3) and the properties of Gauss sums, we have
This proves formula (I).
To prove formula (II), note that if , then must be an odd character modp (i.e., ) so that
or
If , then there exists one character such that . Note that and ; from the properties of Gauss sums, we have
This proves Lemma 2. □
3 Proof of the theorems
In this section, we complete the proof of our theorems. First we prove Theorems 1 and 2. Let , . If , we can assume , then from Lemma 1, the properties of a reduced residue system modp and Gauss sums, we have
If and , then from the method of proving (2.2), we have
From this identity and the method of proving (3.1), we may immediately deduce that if , then
If and , then χ must be a d th character modp, so there exists a character such that . Let be a d-order character modp, then we have
Let , then repeat the process of proving (2.1), (2.2) and (2.3). Combining (3.1), (3.2) and (3.3), we may immediately deduce the estimate
Now note that , Theorems 1 and 2 follow from (3.1), (3.2) and (3.4).
Now we prove Theorem 3. If , we separate q into two cases and . If , then note that for any q th non-residue , we have
From (I) of Lemma 2, we can deduce that
If , then from the method of proving (2.1) and the properties of Gauss sums, we can deduce that
If and , then applying (II) of Lemma 2, we have
Therefore, from (3.5) we can deduce that
This proves Theorem 3.
To prove the corollary, note that
From (3.5) we may immediately deduce the identity
where r and s are any two integers such that .
This completes the proof of our corollary.
References
Chowla S: On Kloosterman’s sum. Norske Vid. Selsk. Forh., Trondheim 1967, 40: 70–72.
Malyshev AV: A generalization of Kloosterman sums and their estimates. Vestn. Leningr. Univ. 1960, 15: 59–75. (in Russian)
Zhang W: On the fourth power mean of the general Kloosterman sums. Indian J. Pure Appl. Math. 2004, 35: 237–242.
Cochrane T, Zheng Z: Bounds for certain exponential sums. Asian J. Math. 2000, 4: 757–774.
Cochrane T, Zheng Z: Upper bounds on a two-term exponential sums. Sci. China Ser. A 2001, 44: 1003–1015. 10.1007/BF02878976
Cochrane T, Zheng Z: Pure and mixed exponential sums. Acta Arith. 1999, 91: 249–278.
Cochrane T, Pinner C: A further refinement of Mordell’s bound on exponential sums. Acta Arith. 2005, 116: 35–41. 10.4064/aa116-1-4
Cochrane T, Pinner C: Using Stepanov’s method for exponential sums involving rational functions. J. Number Theory 2006, 116: 270–292. 10.1016/j.jnt.2005.04.001
Weil A: On some exponential sums. Proc. Natl. Acad. Sci. USA 1948, 34: 204–207. 10.1073/pnas.34.5.204
Burgess DA: On Dirichlet characters of polynomials. Proc. Lond. Math. Soc. 1963, 13: 537–548. 10.1112/plms/s3-13.1.537
Apostol TM: Introduction to Analytic Number Theory. Springer, New York; 1976.
Granville A, Soundararajan K: Large character sums: pretentious characters and the Pólya-Vinogradov theorem. J. Am. Math. Soc. 2007, 20: 357–384. 10.1090/S0894-0347-06-00536-4
Zhang W, Yao W: A note on the Dirichlet characters of polynomials. Acta Arith. 2004, 115: 225–229. 10.4064/aa115-3-3
Zhang W, Yi Y: On Dirichlet characters of polynomials. Bull. Lond. Math. Soc. 2002, 34: 469–473. 10.1112/S0024609302001030
Zhang W, Li H: Elementary Number Theory. Shaanxi Normal University Press, Xi’an; 2008.
Acknowledgements
The authors would like to thank the referee for carefully examining this paper and providing a number of important comments. This work is supported by the N.S.F. of P.R. China (11071194, 61202437), and by the Youth Science and Technology Innovation Foundation of Xi’an Shiyou University (2012QN012).
Author information
Authors and Affiliations
Corresponding author
Additional information
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
YL carried out the upper bound estimate problem of one kind sums analogous to the high-dimensional Kloosterman sums. DH participated in the research and summary of the study.
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
About this article
Cite this article
Li, Y., Han, D. A sum analogous to the high-dimensional Kloosterman sums and its upper bound estimate. J Inequal Appl 2013, 130 (2013). https://doi.org/10.1186/1029-242X-2013-130
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/1029-242X-2013-130