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Friday, 20 July 2007

nt.number theory - Bounding archimedean lengths of fundamental units

Suppose K is a number field, r=r1+r21 (the rank of the unit group) and u1,dots,ur are a basis of fundamental units. Suppose this basis minimizes the max over i=1,dots,r of the largest archimedean absolute value of ui, and this value is M>0. What is a good upper bound on M in terms of standard invariants of the field K? (In fact, I know one exists which for fixed degree is exponential in the regulator.)



More precisely, I'd like a bound on this minimax (min over choices of basis of max over basis elements) of the product of all archimedean absolute values which are greater than 1 (a.k.a. the "entropy") of the ui. (This can of course be bounded by an r1st power of the previous bound.)



Is there a better bound/standard reference for bounding these quantities?

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