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'Kronecker's Jugendtraum'
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| Title of object: |
Kronecker's Jugendtraum |
| Canonical Name: |
KroneckersJugendtraum |
| Type: |
Definition |
| Created on: |
2005-02-08 19:57:55 |
| Modified on: |
2005-02-09 23:59:17 |
| Classification: |
msc:11R37 |
Revision comment (for changes between this and next version):
| Changes for correction #5862 ('spelling'). |
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Content:
Kronecker's Jugendtraum (Jugendtradum is German for "youthful dream") describes a central problem in class field theory, to explicitly describe the abelian extensions of an arbitrary number field $K$ in \PMlinkescapetext{terms} of values of transcendental functions.
Class field theory gives a \PMlinkescapetext{complete} solution to this problem in the case where $K=\mathbb{Q}$, the field of rational numbers. Specifically, the Kronecker-Weber theorem gives that any \PMlinkescapetext{abelian} number field sits inside one of the cyclotomic fields $\mathbb{Q}(\zeta_n)$ for some $n$. Refining this only slightly gives that we can explicitly generate all abelian extensions of $\mathbb{Q}$ by adjoining values of the transcendental function $e^{2\pi iz}$ for certain points $z\in \Q/\Z$.
A slightly more complicated example is when $K$ is a quadratic imaginary extension of $\mathbb{Q}$, in which case Kronecker's Jugendtraum has been solved by the theory of "complex multiplication" (see CM-field). The specific transcendental functions which generate all these abelian extensions are the $j$-function (as in elliptic curves) and Weber's $w$-function.
Though there are partial results in the cases of CM-fields or real quadratic fields, the problem is largely still \PMlinkname{open}{OpenQuestion}, and earned great prestige by being included as Hilbert's twelfth problem. |
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