Isometries of Clifford Algebras I

Let $V$ be a finite dimensional vector space over a field $F$ of characteristic different from 2, and let $Q$ be a nondegenerate, symmetric, bilinear form on $V$. Let $C\mathrm{\ell }(V,Q)$ be the Clifford algebra determined by $V$ and $Q$. The bilinear form $Q$ extends in a natural way to a nondegenerate, symmetric, bilinear form $\bar{Q}$ on $C\mathrm{\ell }(V,Q)$. Let $G$ be the group of isometries of $C\mathrm{\ell }(V,Q)$ relative to $\bar{Q}$, and let $LG$ be the Lie algebra of infinitesimal isometries of $C\mathrm{\ell }(V,Q)$ relative to $\bar{Q}$. We derive some basic structural information about $LG$, and we compute $G$ in the case that $F=R,V=R^n$ and $Q$ is positive definite on $R^n$. In a sequel to this paper we determine $LG$ in the case that $F=R,V=R^n$ and $Q$ is nondegenerate on $R^n$.