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The real J-homomorphism produces cyclic subgroups of size the denominator of $\zeta(1-2k)=-B_{2k}/k$ for $k>0$ in $\pi_{4k-1}S$ which completely account for first layer of the chromatic filtration on $\pi_*S$.

Question: Does the numerator in $\zeta(1-2k)$ also relate to $\pi_*S$ (at higher layers in the chromatic filtration)?

Guess: Can we think of denominator of $\zeta(1-2k)$ as local information (since it is hit by the J-homomorphism) and the numerator of $\zeta(1-2k)$ as global information?

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    $\begingroup$ For those number theorists among us who are not soooo hip to homotopy theory: in words, what is $S$? (Hard to google with just symbols, even with "chromatic filtration"). Thanks! :) $\endgroup$ Commented Jul 27, 2022 at 20:25
  • $\begingroup$ S is the sphere spectrum. This is a modern writing convention. $\endgroup$
    – Ola Sande
    Commented Jul 27, 2022 at 20:27
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    $\begingroup$ Thanks! I understand that it's surely a standard convention in some context, but/and outsiders with curiosity about these interconnections may be out of the loop! :) $\endgroup$ Commented Jul 27, 2022 at 20:30
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    $\begingroup$ The numerators of zeta-values in the left half-plane come from H^1 of class group Iwasawa modules. Those Iwasawa modules contribute to the etale H^* of the number rings and hence to algebraic K-thy, which is why you see numerators of zeta-values in the Lichtenbaum conjecture. But for finite spectra (rather than alg. K-thy spectra), it's much easier to recognize the UNIT group Iwasawa modules as contributing to the homotopy groups of finite spectra, since the Galois action on unit groups in some familiar Z_p-towers agrees with the action of Adams operations on K-theory of some familiar spaces. $\endgroup$
    – user164898
    Commented Jul 27, 2022 at 22:32
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    $\begingroup$ (The cohomology of UNIT group Iwasawa modules contributes to the denominators, rather than numerators, of Dedekind zeta-values in the left half-plane; this is part of the Iwasawa main conjecture) $\endgroup$
    – user164898
    Commented Jul 27, 2022 at 22:33

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(Too long for a comment:)

As A.S. commented, the absolute value of $\zeta(1-2k) = - B_{2k}/2k$ for $k\ge1$ is realized as twice the order of $K_{4k-2}(Z)$ divided by the order of $K_{4k-1}(Z)$, so for Bernoulli numbers the connection to the algebraic K-theory spectrum $K(Z)$ is much stronger than the connection to the sphere spectrum $S$

Implicitly completing at an odd prime $p$, $K_{4k-2}(Z)$ comes from $H_{et}^2(Z[1/p]; Z_p(2k))$ and $K_{4k-1}(Z)$ comes from $H_{et}^1(Z[1/p]; Z_p(2k))$. After (chromatic) $K(1)$-localization, $L_{K(1)} K(Z)$ is more-or-less the $G$-homotopy fixed points for an action on complex topological K-theory, $KU$, where $G$ has cohomological dimension two. Similarly, the image-of-J spectrum $L_{K(1)} S$ is the $\bar G$-homotopy fixed points of $KU$, where $\bar G$ is the quotient of $G$ generated by Adams operations, whose cohomology realizes $H^1$ of $G$ but not $H^2$. The projection $G \to \bar G$ is compatible with the unit map $S \to K(Z)$. Now $K(Z)$ is essentially $K(1)$-local, so this suggests that both the numerator and the denominator of $\zeta(1-2k)$ is accounted for by a $K(1)$-local object. This also fits with the Kummer congruences, telling you that whether a prime $p$ divides $B_{2k}/2k$ depends on $2k$ mod $p-1$, so that any $p$-torsion in $K_{4k-2}(Z)$ will reappear (in some form) every $2p-2$ degrees. This is the usual degree of $v_1$-periodicity. See Dwyer-Mitchell "On the K-theory spectrum of a ring of algebraic integers" K-Theory 14 (1998), no. 3, 201–263, for more general rings of integers than $Z$.

Higher chromatic periodicities tend to repeat every $|v_n| = 2p^n-2$ degrees, which for $n\ge2$ does not match with the Kummer congruences. However, some $v_2$-periodic and $v_3$-periodic families in $\pi_*(S)$ are known to be detected in $\pi_* K(BP\langle 1\rangle)$ and $\pi_* K(BP\langle 2\rangle)$, respectively, where the truncated Brown-Peterson spectrum $BP\langle 1\rangle$ is closely related to topological K-theory, and $BP\langle 2\rangle$ is related to elliptic cohomology and topological modular forms. See Angelini-Knoll-Ausoni-Culver-Hoening-R. https://arxiv.org/abs/2204.05890. These are instances of the phenomenon I called "redshift", which has now been proved to hold for all $E_\infty$ (= strictly commutative) ring spectra by Burklund-Schlank-Yuan https://arxiv.org/abs/2207.09929. Moreover, all of $\pi_*(S)$ is detected in $\pi_* K(S)$. So the higher chromatic families in $\pi_*(S)$ are detected in algebraic K-theory of (non-discrete) ring spectra, and should be detected in arithmetic cohomology theories evaluated on these ring spectra. See Hahn-Raksit-Wilson https://arxiv.org/abs/2206.11208. I am not aware of any extant theory of zeta- or L-functions that reflects these "spectral" cohomology theories.

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