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Ivancevic_Applied-Diff-Geom

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668 <strong>Applied</strong> <strong>Diff</strong>erential <strong>Geom</strong>etry: A Modern IntroductionE is called a Clifford module over a Clifford algebra C(V ) if there is aClifford action·cC(V ) × E −→ E( a , e ) ↦−→ a · ecor equivalently, an algebra homomorphismcC(V ) −→ End(E)a ↦−→ c(a)which is even with respect to this grading:with c(a) (e) = a ·c e,C + (V ) · E ± ⊂ E ± , C − (V ) · E ∓ ⊂ E ∓ .ccLet O(V, Q) be the group of linear transformations of V which preserveQ. That means for all φ ∈ O(V, Q) and v 1 , v 2 ∈ V,Q(φ v 1 , φv 2 ) = Q(v 1 , v 2 ).The action of O(V, Q) on generators of T (V ) is defined byφ(v 1 ⊗ v 2 ⊗ · · · ⊗ v k ) =k∑v 1 ⊗ · · · ⊗ φ(v i ) ⊗ · · · ⊗ v ki=1and extends to the whole T (V ) linearly.I Q is invariant under the action of O(V, Q). Hence C(V, Q) carries anatural action of O(V, Q).Let ∗ : a ↦→ a ∗ be the anti–automorphism of T (V ) induced by v ↦→ −von T , and satisfiesHence,Since(v 1 v 2 . . . v k ) ∗ =(a 1 a 2 ) ∗ = a ∗ 2 a ∗ 1.{(vk v k−1 . . . v 1 ), if k is even,−(v k v k−1 . . . v 1 ),v ∗ 1 ⊗ v ∗ 2 + v ∗ 2 ⊗ v ∗ 1 + 2Q(v ∗ 1, v ∗ 2)if k is odd.= (−v 1 ) ⊗ (−v 2 ) + (−v 2 ) ⊗ (−v 1 ) + 2Q(−v 1 , −v 2 )= v 1 ⊗ v 2 + v 2 ⊗ v 1 + 2Q(v 1 , v 2 ),

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