Monday, 12 December 2011

kt.k theory homology - Any reason why K_23(Z) has order 65520?

More generally, if F is a number field with ring of integers mathfrako, and zetaaFst(m) is the first nonzero coefficient in the Taylor expansion of zetaF at m, then Lichtenbaum (and Quillen) conjectured that |zeta_F^ast(1-i)|=frac{# K_{2i-2}(mathfrak{o})_{text{tors}}}{# K_{2i-1}(mathfrak{o})_{text{tors}}}, times a regulator and some power of 2 (which I believe is not understood in general, although some progress was made on this in Ion Rada's PhD thesis). Hence, odd K groups are related to the denominators of the Bernoulli numbers, and the even ones are related to the numerators. Also, not much cancellation occurs; I think the two K-groups can only share factors of 2.



The Voevodsky-Rost theorem might prove the Lichtenbaum conjecture, but I haven't seen anyone come out and say definitely that this is the case.



I don't have much intuition for this, except that the K-groups seem to be objects that like to map into étale cohomology groups. In this paper (link to MathSciNet), Soulé constructs Chern class maps from certain K-groups to étale cohomology groups. Furthermore, these maps frequently have small (or trivial) kernels and cokernels. I suppose the idea, then, is that K-theory is supposed to be a slightly better behaved version of étale cohomology, at least for the purpose of understanding zeta functions.



The rank of K-groups of rings of integers was computed by Quillen in the early 70's: it's rank 1 in dimension 0, rank r1+r21 in dimension 1 (Dirichlet's unit theorem), rank 0 in even dimensions >0, rank r1+r2 in dimensions 1pmod4 except 1, and rank r2 in dimensions 3pmod4.

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