eva.bayer@epfl.ch

Submission: 2011, Dec 4

Let $k$ be a field of characteristic not 2. A quadratic space is
a non--degenerate symmetric bilinear form $q: V \times V \to k$
defined on a finite dimensional $k$--vector space $V$, and an
isometry of $(V,q)$ is an element of $SO(q)$, in other words an
isomorphism $t : V \to V$ such that $q(tx,ty) = q(x,y)$ for all
$x,y \in V$ and that $det (t) = 1$. Milnor investigated
isometries of quadratic spaces, and raised the following
question :

Question. Let $q$ be a quadratic space over $k$, and let $f \in
k[X]$ be an irreducible polynomial. How can we tell whether $q$
has an isometry with minimal polynomial $f$ ?

The purpose of the present paper is to study and give an answer to this
question for global fields.

2010 Mathematics Subject Classification: 11E12

Keywords and Phrases:

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