English

Asymptotic expansions for the alternating Hurwitz zeta function and its derivatives

Number Theory 2023-08-10 v6 Classical Analysis and ODEs

Abstract

Let ζE(s,q)=n=0(1)n(n+q)s \zeta_E(s,q)=\sum_{n=0}^\infty\frac{(-1)^n}{(n+q)^{s}} be the alternating Hurwitz (or Hurwitz-type Euler) zeta function. In this paper, we obtain the following asymptotic expansion of ζE(s,q)\zeta_{E}(s,q) ζE(s,q)12qs+14sqs112qsk=1E2k+1(0)(2k+1)!(s)2k+1q2k+1, \zeta_E(s,q)\sim\frac12 q^{-s}+\frac14sq^{-s-1}-\frac12q^{-s}\sum_{k=1}^\infty\frac{E_{2k+1}(0)}{(2k+1)!}\frac{(s)_{2k+1}}{q^{2k+1}}, as q|q|\to\infty, where E2k+1(0)E_{2k+1}(0) are the special values of odd-order Euler polynomials at 0, and we also consider representations and bounds for the remainder of the above asymptotic expansion. In addition, we derive the asymptotic expansions for the higher order derivatives of ζE(s,q)\zeta_{E}(s,q) with respect to its first argument ζE(m)(s,q)msmζE(s,q),\zeta_{E}^{(m)}(s,q)\equiv\frac{\partial^m}{\partial s^m}\zeta_E(s,q), as q|q|\to\infty. Finally, we also prove a new exact series representation of ζE(s,q)\zeta_{E}(s,q).

Keywords

Cite

@article{arxiv.2103.15528,
  title  = {Asymptotic expansions for the alternating Hurwitz zeta function and its derivatives},
  author = {Su Hu and Min-Soo Kim},
  journal= {arXiv preprint arXiv:2103.15528},
  year   = {2023}
}

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31 pages