q-RIEMANN ZETA FUNCTION

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q-RIEMANN ZETA FUNCTION

TAEKYUN KIM Received 19 July 2003

We consider the modifiedq-analogue of Riemann zeta function which is defined byζq(s)=

_∞

n=1(q^n(s−1)/[n]^s), 0< q <1,s∈C. In this paper, we giveq-Bernoulli numbers which can be viewed as interpolation of the aboveq-analogue of Riemann zeta function at negative integers in the same way that Riemann zeta function interpolates Bernoulli numbers at negative integers. Also, we will treat some identities of q-Bernoulli numbers using non- Archimedeanq-integration.

2000 Mathematics Subject Classification: 11S80, 11B68.

1. Introduction. Throughout this paper,Zp,Qp,C, andCpwill respectively denote the ring ofp-adic rational integers, the field ofp-adic rational numbers, the complex number field, and the completion of algebraic closure ofQp.

Thep-adic absolute value inCpis normalized so that|p|p=1/p. When one talks of q-extension,qis considered in many ways such as an indeterminate, a complex number q∈C, or ap-adic numberq∈Cp. Ifq∈C, we normally assume|q|<1. Ifq∈Cp, then we normally assume|q−1|p< p^−1/(p−1)so thatq^x=exp(xlogq)for|x|p≤1. We use the notation

[x]=[x:q]=1−q^x

1−q =1+q+q²+···+q^x−1. (1.1)

Note that lim_q→1[x]=xforx∈Zpin thep-adic case.

LetUD(Zp)be denoted by the set of uniformly differentiable functions onZp. Forf∈UD(Zp), we start with the expression

1

p^N

0≤j<p^N

q^jf (j)=

0≤j<p^N

f (j)µq

j+p^NZp

(1.2)

representing the analogue of Riemann’s sums forf(cf. [4]).

The integral off onZp will be defined as the limit(N→ ∞)of these sums, which exists. Thep-adicq-integral of a functionf∈UD(Zp)is defined by (see [4])

Zp

f (x)dµq(x)= lim

N→∞

1

p^N

0≤j<p^N

f (j)q^j. (1.3)

Fordthat is a fixed positive integer with(p,d)=1, let X=Xd=lim←_N Z

dp^NZ, X¹=Zp, X^∗=

0<a<dp (a,p)=1

a+dpZp, a+dp^NZp= x∈X|x≡a

moddp^N ,

(1.4)

wherea∈Zlies in 0≤a < dp^N.

Let N be the set of positive integers. For m,k ∈N, theq-Bernoulli polynomials, β^(−m,k)m (x,q), of higher order for the variablexinCpare defined usingp-adicq-integral by (cf. [4])

β^(−m,k)m (x,q)

=

Zp

Zp

···

Zp

ktimes

x+x1+x2+···+xk

m

·q^{−x1(m+1)−x2}(m+2)−···−x_k(m+k)dµq

x1

dµq

x2

···dµq

xk

. (1.5)

Now, we define theq-Bernoulli numbers of higher order as follows (cf. [2,4,7]):

β^(−m,k)m

=β^(−m,k)m (q)

=β^(−m,k)m (0,q). (1.6)

By (1.5), it is known that (cf. [4])

β^(−m,k)_m =lim

N→∞

1 p^Nk

p^N−1 x1=0

···

p^N−1 x_k=0

x1+···+xkm

q^−x1m−x2(m+1)+···−x_k(m+k−1)

= 1 (1−q)^m

m i=0

m i

(−1)ⁱ(i−m)(i−m−1)···(i−m−k+1) [i−m][i−m−1]···[i−m−k+1],

(1.7)

where

m i

are the binomial coefficients.

Note that lim_q→1β^(−m,k)m =Bm^(k), whereBm^(k)are ordinary Bernoulli numbers of orderk (cf. [2,3,5,7,9]). By (1.5) and (1.7), it is easy to see that

β^(−m,1)m (x,q)= m i=0

m i

q^xiβ^(−m,1)_i [x]^m−i

= 1 (1−q)^m

m j=0

q^jx m

j

(−1)^j j−m [j−m].

(1.8)

We modify theq-analogue of Riemann zeta function which is defined in [1] as follows:

forq∈Cwith 0< q <1,s∈C, define

ζq(s)= ∞ n=1

q^(s−1)n

[n]^s . (1.9)

q-RIEMANN ZETA FUNCTION

The numerator ensures the analytic continuation for(s) >1. In (1.9), we can consider the following problem.

“Are there q-Bernoulli numbers which can be viewed as interpolation ofζq(s)at negative integers in the same way that Riemann zeta function interpolates Bernoulli numbers at negative integers?”

In this paper, we give the valueζq(−m)form∈N, which is the answer of the above problem, and construct a new complexq-analogue of Hurwitz’s zeta function andq-L- series. Also, we will treat some interesting identities ofq-Bernoulli numbers.

2. Some identities ofq-Bernoulli numbersβ^(−m,1)m . In this section, we assumeq∈Cp

with|1−q|p< p^−1/(p−1). By (1.5), we have β^(−n,1)_n (x,q)=

Xq^−(n+1)t[x+t]ⁿdµq(t)

=[d]ⁿ⁻¹

d−1

i=0

q⁻ⁿⁱ

Zp

q^−(n+1)dx x+i

d :q^d n

dµ_qd(x).

(2.1)

Thus, we have

β^(−n,1)_n (x,q)=[d]ⁿ⁻¹

d−1

i=0

q⁻ⁿⁱβ^(−n,1)_n x+i

d ,q^d

, (2.2)

whered,nare positive integers.

If we takex=0, then we have

[n]β^(−m,1)m −n[n]^mβ^(−m,1)m

qⁿ

=

m−1 k=0

m k

[n]^kβ^(−m,1)_k qⁿⁿ⁻¹

j=1

q^−(m−j)k[j]^m−k. (2.3) It is easy to see that lim_q→1β^(−m,1)m =Bm, whereBm are ordinary Bernoulli numbers (cf. [7]).

Remark2.1. By (2.3), note that

n 1−n^m

Bm=

m−1

k=0

m k

n^kBk

n−1

j=1

j^m−k. (2.4)

LetFq(t)be the generating function ofβ^(−n,1)n as follows:

Fq(t)= ∞ k=0

β^(−k,1)_k t^k

k!. (2.5)

By (1.7) and (2.5), we easily see that

Fq(t)= − ∞ m=0

m

∞ n=0

q^−mn[n]^m−1 t^m

m!. (2.6)

Through differentiating both sides with respect totin (2.5) and (2.6), and comparing coefficients, we obtain the following proposition.

Proposition2.2. Form >0, there exists

−β^(−m,1)m

m =

∞ n=1

q^−nm[n]^m−1. (2.7)

Moreover,β^(0,1)0 =(q−1)/logq.

Remark2.3. Note thatProposition 2.2is aq-analogue ofζ(1−2m)for any positive integerm.

Letχbe a primitive Dirichlet character with conductorf∈N. Form∈N, we define

β^(−m,1)m,χ =

Xq^−(m+1)xχ(x)[x]^mdµq(x), form≥0. (2.8) Note that

β^(−m,1)m,χ =[d]^m−1

d−1 i=0

χ(i)q^−miβ^(−m,1)m

i d,q^d

. (2.9)

3. q-analogs of zeta functions. In this section, we assumeq∈Cwith|q|<1. In [1], theq-analogue of Riemann zeta function was defined by (cf. [1])

ζq^∗(s)= ∞ n=1

q^ns

[n]^s, (s) >0. (3.1)

Now, we modify the aboveq-analogue of Riemann zeta function as follows: forq∈C with 0<|q|<1,s∈C, define

ζq(s)= ∞ n=1

q^(s−1)n

[n]^s . (3.2)

By (2.5), (2.6), and (2.7), we obtain the following proposition.

Proposition3.1. Form∈N, there exists (i) ζq(1−m)= −β^(−m,1)m /m, form≥1;

(ii) ζq(s)having simple pole ats=1with residue(q−1)/logq. By (1.7) and (1.8), we see that

β^(−n,1)n (x,q)= −n ∞ k=0

[k]q^x+[x]n−1

q^−n(k+x), where 0≤x <1. (3.3)

q-RIEMANN ZETA FUNCTION

Hence, we can defineq-analogue of Hurwitzζ-function as follows: fors∈C, define

ζq(s,x)= ∞ n=0

q^(s−1)(n+x)

[n]q^x+[x]s. (3.4)

Note thatζq(s,x)has an analytic continuation inCwith only one simple pole ats=1.

By (3.3) and (3.4), we have the following theorem.

Theorem3.2. For any positive integerk, there exists

ζq(1−k,x)= −β^(−k,1)_k (x,q)

k . (3.5)

Letχbe Dirichlet character with conductord∈N. By (2.9), the generalizedq-Bernoulli numbers withχcan be defined by

β^(−m,1)_m,χ =[d]^m−1

d−1

i=0

χ(i)q^−miβ^(−m,1)_m i

d,q^d

. (3.6)

Fors∈C, we define

Lq(s,χ)=^∞

n=1

χ(n)q^(s−1)n

[n]^s . (3.7)

It is easy to see that

Lq(χ,s)=[d]^−s d a=1

χ(a)q^(s−1)aζ_qd

s,a

d

. (3.8)

By (3.6), (3.7), and (3.8), we obtain the following theorem.

Theorem3.3. Letkbe a positive integer. Then there exists

Lq(1−k,χ)= −β^(−k,1)_k,χ

k . (3.9)

LetaandFbe integers with 0< a < F. Fors∈C, we consider the functionsHq(s,a,F) as follows:

Hq(s,a,F)=

m≡a(F),m>0

q^m(s−1)

[m]^s =[F]^−sζq^F

s,a

F

. (3.10)

Then we have

Hq(1−n,a,F)= −[F]ⁿ⁻¹ n β^(−n,1)_n

a F,q^F

, (3.11)

wherenis any positive integer.

Therefore, we obtain the following theorem.

Theorem3.4. LetaandF be integers with0< a < F. Fors∈C, there exists (i) Hq(1−n,a,F)= −([F]ⁿ⁻¹/n)β^(−n,1)n (a/F,q^F);

(ii) Hq(s,a,F)having a simple pole ats=1with residue(1/[F]F)((q^F−1)/logq). In a recent paper, theq-analogue of Riemann zeta function was studied by Cherednik (see [1]). In [1], we can consider theq-Bernoulli numbers which can be viewed as an interpolation of theq-analogue of Riemann zeta function at negative integers. In this paper, we have shown that the q-analogue of zeta function interpolates q-Bernoulli numbers at negative integers in the same way that Riemann zeta function interpolates Bernoulli numbers at negative integers (cf. [2,5,7]).

Remark3.5. Letq∈Cpwith|1−q|p< p^−1/(p−1). Then thep-adicq-gamma function was defined as (see [8])

Γp,q(n)=(−1)ⁿ

1≤j<n,(j,p)=1

[j]. (3.12)

For allx∈Zp, we have

Γp,q(x+1)=p,q(x)Γp,q(x), (3.13) wherep,q(x)= −[x]for|x|p=1, andp,q(x)= −1 for|x|p<1, (see [8]). By (3.13), we easily see that (cf. [6])

logΓp,q(x+1)=logp,q(x)+logΓp,q(x). (3.14) By the differentiation of both sides in (3.14), we have (cf. [6])

Γ_p,q (x+1)

Γp,q(x+1)=Γ_p,q (x)

Γp,q(x)+_p,q(x)

p,q(x). (3.15)

By (3.15), we easily see that (cf. [6]) Γp,q (x) Γp,q(x)=



^x−1

j=1

q^j [j]



logq

q−1+Γp,q (1)

Γp,q(1). (3.16)

Define

Lp,q(x)=

x−1 j=0

p,q(j)

p,q(j). (3.17)

It is easy to check thatLp,q(1)=0. By (3.15), we also see that Γp,q (x)

Γp,q(x)=Lp,q(x)+Γp,q (1)

Γp,q(1), forx∈Zp, (3.18)

q-RIEMANN ZETA FUNCTION

whereLp,q(x)denotes the indefinite sum of_p,q(x)/p,q(x). By using (3.18) after sub- stitutingx=1, we obtainLp,q(1)=0. The classical Euler constant was known asγ=

−Γ(1)/Γ(1). In [8], Koblitz defined thep-adicq-Euler constantγp,q= −Γp,q (1)/Γp,q(1) (cf. [6,8]). By using (3.16) and the congruence of Andrews (cf. [3]), we obtain the follow- ing congruence:

q−1 logq

Γp,q (p) Γp,q(p)−γp,q

=

p−1 j=1

q^j

[j]≡p−1 2 (q−1)

mod[p]

. (3.19)

Acknowledgments. The author expresses his gratitude to the referees for their valuable suggestions and comments. This work was supported by the Korea Research Foundation Grant (KRF-2002-050-C00001).

References

[1] I. Cherednik,Onq-analogues of Riemann’s zeta function, Selecta Math. (N.S.)7(2001), no. 4, 447–491.

[2] T. Kim,On explicit formulas ofp-adicq-L-functions, Kyushu J. Math.48(1994), no. 1, 73–86.

[3] ,On p-adicq-L-functions and sums of powers, Discrete Math.252(2002), no. 1–3, 179–187.

[4] ,q-Volkenborn integration, Russ. J. Math. Phys.9(2002), no. 3, 288–299.

[5] ,Non-archimedeanq-integrals associated with multiple Changheeq-Bernoulli polyno- mials, Russ. J. Math. Phys.10(2003), 91–98.

[6] T. Kim, L. C. Jang, K-H. Koh, and I.-S. Pyung,A note on analogue ofΓ-functions, Proceedings of the Conference on 5th Transcendental Number Theory, vol. 5, no. 1, Gakushuin University, Tokyo, 1997, pp. 37–44.

[7] T. Kim and S.-H. Rim,Generalized Carlitz’sq-Bernoulli numbers in thep-adic number field, Adv. Stud. Contemp. Math. (Pusan)2(2000), 9–19.

[8] N. Koblitz,q-extension of thep-adic gamma function, Trans. Amer. Math. Soc.260(1980), no. 2, 449–457.

[9] Q.-M. Luo, Z.-L. Wei, and F. Qi,Lower and upper bounds ofζ(3), Adv. Stud. Contemp. Math.

(Kyungshang)6(2003), no. 1, 47–51.

Taekyun Kim: Institute of Science Education, Kongju National University, Kongju 314-701, Korea

E-mail address:[email protected]

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