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Search: MSC category 16K20 ( Finite-dimensional {For crossed products, see 16S35} )

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1. CJM 2007 (vol 59 pp. 658)

 Division Algebras of Prime Degree and Maximal Galois $p$-Extensions Let $p$ be an odd prime number, and let $F$ be a field of characteristic not $p$ and not containing the group $\mu_p$ of $p$-th roots of unity. We consider cyclic $p$-algebras over $F$ by descent from $L = F(\mu_p)$. We generalize a theorem of Albert by showing that if $\mu_{p^n} \subseteq L$, then a division algebra $D$ of degree $p^n$ over $F$ is a cyclic algebra if and only if there is $d\in D$ with $d^{p^n}\in F - F^p$. Let $F(p)$ be the maximal $p$-extension of $F$. We show that $F(p)$ has a noncyclic algebra of degree $p$ if and only if a certain eigencomponent of the $p$-torsion of $\Br(F(p)(\mu_p))$ is nontrivial. To get a better understanding of $F(p)$, we consider the valuations on $F(p)$ with residue characteristic not $p$, and determine what residue fields and value groups can occur. Our results support the conjecture that the $p$ torsion in $\Br(F(p))$ is always trivial. Category:16K20
 On a Theorem of Hermite and Joubert A classical theorem of Hermite and Joubert asserts that any field extension of degree $n=5$ or $6$ is generated by an element whose minimal polynomial is of the form $\lambda^n + c_1 \lambda^{n-1} + \cdots + c_{n-1} \lambda + c_n$ with $c_1=c_3=0$. We show that this theorem fails for $n=3^m$ or $3^m + 3^l$ (and more generally, for $n = p^m$ or $p^m + p^l$, if 3 is replaced by another prime $p$), where $m > l \geq 0$. We also prove a similar result for division algebras and use it to study the structure of the universal division algebra $\UD (n)$. We also prove a similar result for division algebras and use it to study the structure of the universal division algebra $\UD(n)$. Categories:12E05, 16K20