Convergence question on analytic continuation of Zeta fcn

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Discussion Overview

The discussion revolves around the convergence of the analytic continuation of the Riemann zeta function, particularly focusing on a series derived from Euler's transformation. Participants explore the conditions under which this series converges in the complex plane, especially for values of \( s \) outside the region where the original series converges.

Discussion Character

  • Technical explanation, Exploratory, Debate/contested

Main Points Raised

  • One participant presents a series for the analytic continuation of the zeta function and questions how to demonstrate its convergence for all \( s \) in the complex plane except \( s=1 \).
  • The same participant expresses uncertainty about the convergence of a related series for \( \zeta(-s) \), suggesting a personal intuition that it does not converge.
  • Another participant references a specific academic article that may provide insights into the analytic continuation and convergence of the zeta function, indicating a potential resource for further exploration.
  • A couple of participants express gratitude for the reference provided, indicating its usefulness in the context of the discussion.

Areas of Agreement / Disagreement

There is no consensus on the convergence of the series discussed, as one participant expresses doubt about the convergence of a related series, while others provide references without resolving the uncertainty.

Contextual Notes

The discussion includes assumptions about convergence that are not fully substantiated, and the implications of Euler's transformation on the series are not completely explored.

benorin
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Given \zeta (s) = \sum_{k=1}^{\infty} k^{-s} which converges in the half-plane \Re (s) >1, the usual analytic continuation to the half-plane \Re (s) >0 is found by adding the alternating series \sum_{k=1}^{\infty} (-1)^kk^{-s} to \zeta (s) and simplifing to get

\zeta (s) = \left(1-2^{1-s}\right) ^{-1}\sum_{k=1}^{\infty} \frac{(-1)^{k-1}}{k^s}

now re-index this series to begin with k=0 and apply Euler's series transformation (as given by Knopp: in terms of the backward difference operator; (4) and (5) in the link) to arrive at this series

\zeta (s) = \left(1-2^{1-s}\right) ^{-1}\sum_{k=0}^{\infty}\frac{1}{2^{k+1}} \sum_{m=0}^{k} \left( \begin{array}{c}k\\m\end{array}\right) \frac{(-1)^{m}}{(m+1)^s}

which according to the mathworld Riemann zeta function page formula (20) converges for all s in the complex plane except s=1 (i.e. \forall s\in\mathbb{C}\setminus \left\{ 1\right\} ). My question is, how does one demonstrate the convergence of this series on said domain?

EDIT: I have noticed that

\zeta (-s) = \left(1-2^{1+s}\right) ^{-1}\sum_{k=0}^{\infty}\frac{1}{2^{k+1}} \sum_{m=0}^{k} \left( \begin{array}{c}k\\m\end{array}\right) (-1)^{m}(m+1)^s

does :rolleyes: not at all appear to converge according to that portion of my "gut" that is known to conjecture for me when initially looking at series for convergence. :biggrin:

Thanks, --Ben
 
Last edited:
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See "Analytic Continuation of Riemann's Zeta Function and Values at Negative Integers Via Euler's Transformation of Series", Jonathan Sondow, Proceedings of the American Mathematical Society, Vol. 120, No. 2. (Feb., 1994), pp. 421-424.

If you have access to http://www.jstor.org/cgi-bin/jstor/printpage/00029939/di981511/98p04597/0?frame=noframe&dpi=3&userID=8e9680ea@utoronto.ca/01cc993397005075a23&backcontext=table-of-contents&backurl=/cgi-bin/jstor/listjournal/00029939/di981511%3fframe%3dframe%26dpi%3d3%26userID%3d8e9680ea@utoronto.ca/01cc993397005075a23%26config%3djstor&action=download&config=jstor
 
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Thank you for taking the time to dig that one up, shmoe. Much appreciated.
 
Last edited:
I got said article, and it is a nice reference. Thank you shmoe.
 

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