Let $K$ be a number field, $\mathcal{O}_K$ its ring of integers, $\mathcal{O}_K^{\times}$ its group of units, $\mathcal{Cl}(K)=J_K/P_K$ its ideal class group. As you know, the Dedekind zeta function is defined as follows:

$$\zeta_{K}(s)=\sum_{I\subseteq \mathcal{O}_K}{\frac{1}{(N_{K/\mathbb{Q} }(I))^{s}}}.$$

Let $\mathcal{A} \in \mathcal{Cl}(K)$ be arbitrary, now consider this function:

$$\zeta_{K, \mathcal{A}}^{\text{BAD}}(s)=\sum_{I\subseteq \mathcal{O}_K \\ I \in [\mathcal{A}]}{\frac{1}{(N_{K/\mathbb{Q} }(I))^{s}}}.$$

I did not verify the conditions for absolute convergence, but if there is no serious problem about that, then we have:

$$\zeta_{K}(s) = \sum_{\mathcal{A} \in \mathcal{Cl}(K)} \zeta_{K, \mathcal{A}}^{\text{BAD}}(s).$$

$\color{Red}{\text{My question}}$:

I am very curious to know if the BAD zeta function $\zeta_{K, \mathcal{A}}^{\text{BAD}}(s)$, is a good thing or not? What other objects are related to the BAD zeta function $\zeta_{K, \mathcal{A}}^{\text{BAD}}(s)$? I have very little information about this subject, and I could not find anything about it in the literature. Is there something related to the BAD zeta function $\zeta_{K, \mathcal{A}}^{\text{BAD}}(s)$? Could you please introduce me to some references to follow and read?

  • 1
    $\begingroup$ What does "$I\subseteq\mathcal{O}^\times_K$" mean? $\endgroup$ Jun 13, 2020 at 9:34
  • $\begingroup$ @AnginaSeng +1, you are right. It doesn't make sense. I will edit it now. $\endgroup$
    – Davood
    Jun 13, 2020 at 9:39
  • 1
    $\begingroup$ Why ${}$BAD? $\endgroup$ Jun 13, 2020 at 9:53
  • 3
    $\begingroup$ Your functions are "partial zeta functions". The standard proofs of the analytic class number formula involve using your final sum, and observing that each partial zeta function has a pole at $s=1$ with the same residue. $\endgroup$ Jun 13, 2020 at 10:05
  • 3
    $\begingroup$ See my answer there math.stackexchange.com/a/3713036/276986 we decompose $\zeta_K$ this way because the sum over one ideal class is something closeto the Mellin transform of a theta function, from which we obtain the meromorphic continuation, the residues, the functional equation.. $\endgroup$
    – reuns
    Jun 13, 2020 at 18:32


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy