A note on integral bases of unramified cyclic extensions of prime degree. (English) Zbl 1018.11055
Let \(L/K\) be a finite extension of number fields, unramified at all finite primes, with rings of integers \(O_L, O_K\) and Galois group \(\Gamma\). If \(O_L = O_K[\alpha]\) for some \(\alpha \in O_L\), \(L/K\) is said to have a relative power integral basis (PIB). If \(O_L = O_K[\Gamma](\beta)\) for some \(\beta \in O_L\), \(L/K\) is said to have a relative normal integral basis (NIB). When \(\Gamma\) is cyclic of prime order \(p\) and \(K\) contains a primitive \(p\)th root of unity \(\zeta_p\), the reviewer [Proc. Lond. Math. Soc. (3) 35, 407-422 (1977; Zbl 0374.13002)] showed that if \(L/K\) has a NIB, it has a PIB. The author obtains infinitely many cubic extensions \(L/K\) with \(\zeta_3 \in K\) with a PIB but no NIB, and also infinitely many quadratic extensions \(L/K\) with PIB but no NIB where \(K\) is a real quadratic field. The examples build on earlier results of the author [J. Algebra 235, 104-112 (2001; Zbl 0972.11101)].
Reviewer: Lindsay N.Childs (Albany)
MSC:
11R33 | Integral representations related to algebraic numbers; Galois module structure of rings of integers |
11R11 | Quadratic extensions |
Keywords:
normal integral basis; power integral basis; cubic extension; quadratic extension; real quadratic field; unramified extensionReferences:
[1] | Childs, L., The group of unramified Kummer extensions of prime degree, Proc. London Math. Soc., 35, 407-422 (1977) · Zbl 0374.13002 · doi:10.1112/plms/s3-35.3.407 |
[2] | H. Ichimura, On power integral bases of unramified cyclic extensions of prime degree. To appear inJournal of Algebra. · Zbl 0972.11101 |
[3] | -, On a power integral bases problem over cyclotomic ℤ_p-extensions. To appear inJournal of Algebra. · Zbl 0990.11060 |
[4] | S. Lang,Algebraic Number Theory. Springer, 1986. · Zbl 0601.12001 |
[5] | L. Washington,Introduction to Cyclotomic Fields (2-nd edition). Springer, 1996. · Zbl 0484.12001 |
This reference list is based on information provided by the publisher or from digital mathematics libraries. Its items are heuristically matched to zbMATH identifiers and may contain data conversion errors. In some cases that data have been complemented/enhanced by data from zbMATH Open. This attempts to reflect the references listed in the original paper as accurately as possible without claiming completeness or a perfect matching.