Fields Institute Communications Volume 00, 0000
Valuation Theory on Finite Dimensional Division Algebras
A. R. Wadsworth Department of Mathematics University of California at San Diego La Jolla, California 92093–0112 [email protected]
to P. Ribenboim with respect and affection
Valuation theory has classically meant the study of valuations on a commu- tative field. Such valuation theory has flourished for many decades, nourished by its connections with number theory and algebraic geometry. But there is also a noncommutative side of the subject in the study of valuations and valuation rings on division rings. This aspect has blossomed only in the last twenty odd years, and it is not so well known as its commutative counterpart. We give in this paper a survey of valuations and valuation theory for division rings finite dimensional over their centers. We describe the associated theory and also some of the most significant constructions that have been given as applications. The earliest use of valuations on noncommutative division rings, to my know- ledge, was by Hasse in his work in [Ha] in 1931 on orders over central simple algebras over p-adic fields. In the ’40’s and ’50’s there was a little further work with valua- tions on division algebras over fields with complete discrete valuations. Also, there was some discussion of valuations on division algebras in Schilling’s work [Schi1], [Schi2], mostly observing that some results about valuations remain valid without assuming that the ambient field be commutative. One can speculate that there was little attention to valuations on division algebras because too often for the di- vision algebras of interest there was no apparent valuation available. Additionally, it was not fully clear what to take as the definition of a valuation on a division ring, since the concepts of valuation and valuation ring are not equivalent in the noncommutative setting. It was not until the late 1970’s and the 1980’s that valuation theory on divi- sion algebras began to developsubstantially. This was due in large measure to the realization that some of the major constructions of counterexamples in the 1970’s could best be understood using valuation theory. This applies to Amitsur’s con- struction of noncrossed product division algebras and also to the constructions of division algebras with nontrivial SK1 by Platonov and by Yanchevski˘ı. It began to
2000 Mathematics Subject Classification. Primary 16K20, 12J10; Secondary 16H05, 16K50, 16L30, 19B99.