## Duke Mathematical Journal

### q-series identities and values of certain L-functions

#### Abstract

As usual, define Dedekind's eta-function η(z) by the infinite product

$$\eta(z):=q^{1/24}\prod_{n=1}^{\infty} \big(1-q^n\big) \quad \big(q:=e^{2\pi i z} \text{ throughout}\big).$$

In a recent paper, D. Zagier proved that (note: empty products equal 1 throughout)

$$\sum_{n=0}^{\infty} \Big(\eta(24z)-q\big(1-q^{24}\big) \big(1-q^{48}\big)\cdots \big(1-q^{24n}\big)\Big) =\eta(24z)D(q)+E(q),$$

where the series D(q) and E(q) are defined by

\begin{align*} D(q)&=-\frac{1}{2}+\sum_{n=1}^{\infty}\frac{q^{24n}}{1-q^{24n}}\\ &=-\frac{1}{2}+\sum_{n=1}^{\infty}d(n)q^{24n}\\ &=-\frac{1}{2}+q^{24}+2q^{48}+2q^{72}+3q^{96}+\cdots\quad,\\ E(q)&=\frac{1}{2}\sum_{n=1}^{\infty} \bigg(\frac{12}{n}\bigg)nq^{n^2} =\frac{1}{2}q-\frac{5}{2}q^{25}- \frac{7}{2}q^{49}+\frac{11}{2}q^{121}+\cdots\quad. \end{align*}

Here d(n) denotes the number of positive divisors of n. We obtain two infinite families of such identities and describe some consequences for L-functions and partitions. For example, if χ2 is the Kronecker character for ℚ($\sqrt{2}$), these identities can be used to show that

\begin{align*} &-2e^{-t/8}\sum_{n=0}^{\infty} \frac{\big(1-e^{-2t}\big)\big(1-e^{-4t}\big) \cdots\big(1-e^{-2nt}\big)} {\big(1+e^{-t}\big)\big(1+e^{-3t}\big) \cdots\big(1+e^{-(2n+1)t}\big)} \\ &\hspace{110pt}=\sum_{n=0}^{\infty} \bigg(\frac{-1}{8}\bigg)^n\cdot L(\chi_{2},-2n-1)\cdot \frac{t^{n}}{n!}. \end{align*}

#### Article information

Source
Duke Math. J., Volume 108, Number 3 (2001), 395-419.

Dates
First available in Project Euclid: 5 August 2004

https://projecteuclid.org/euclid.dmj/1091737179

Digital Object Identifier
doi:10.1215/S0012-7094-01-10831-4

Mathematical Reviews number (MathSciNet)
MR1838657

Zentralblatt MATH identifier
1005.11048

#### Citation

Andrews, George E.; Jiménez-Urroz, Jorge; Ono, Ken. q -series identities and values of certain L -functions. Duke Math. J. 108 (2001), no. 3, 395--419. doi:10.1215/S0012-7094-01-10831-4. https://projecteuclid.org/euclid.dmj/1091737179

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