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19 votes
Accepted

how to compute Hilbert class field of $\Bbb Q(\zeta_{23})$?

The cyclotomic field $K=\mathbb{Q}(\zeta_{23})$ contains the quadratic field $F=\mathbb{Q}(\sqrt{-23})$, and $F$ has class number $3$ (it is the first quadratic field, when those are ordered by absolu …
Alex B.'s user avatar
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14 votes
2 answers
1k views

Class groups in dihedral extensions - some sort of Spiegelungssatz?

Let $p$ be an odd prime and let $F/\mathbb{Q}$ be a Galois extension with Galois group $D_{2p}$, let $K$ be the intermediate quadratic extension of $\mathbb{Q}$, and $L$ an intermediate degree $p$ ext …
Alex B.'s user avatar
  • 13k
12 votes

An explicit computation in class field theory

In your particular case, $K^{ab}$ is completely understood, but your field is one of the very few for which such an explicit class field theory is known, so you got lucky. I don't know your backgroun …
Alex B.'s user avatar
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8 votes

How do Brauer groups relate to zeta functions?

The computation of the Brauer group is only the "first half" of class field theory. The main reason one is interested in the Brauer group is that for a finite Galois extension $L/K$, let's say of loca …
Alex B.'s user avatar
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7 votes
Accepted

Analogue of j-invariant for CM fields

The simplest generalisation to abelian surfaces is, I believe, the statement (which is a theorem, not a conjecture) that the Igusa invariants of an abelian surface with CM by $K$ generate an abelian u …
Alex B.'s user avatar
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