Bourbaki

Proposition 38

Tag 0AAZ, permanent. Cite it as [Bourbaki, Tag 0AAZ].

Lie Groups and Lie Algebras, chapter III, § 3. Passage from a Lie group to its Lie algebra

Consider GG as operating on EE on the left by the mapping (g,x)↦π(g)x(g, x) \mapsto \pi(g)x. Let b∈Eb \in E and φ(b)\varphi(b) be its orbital mapping. Let Tb(E)T_b(E) be canonically identified with EE. For all t∈L(G)t \in L(G),

(L(π)t)(b)=⟨t,φ(b)⟩=φ(b)∗t=t∗εb. (L(\pi)t)(b) = \langle t, \varphi(b) \rangle = \varphi(b)*t = t * \varepsilon_b.

In particular, the vector field defined by tt on EE is the field b↦(L(π)t)(b)b \mapsto (L(\pi)t)(b).

L(π)t=⟨t,π⟩L(\pi)t = \langle t, \pi \rangle (no. 9, Proposition 34). As the mapping A↦AbA \mapsto Ab of L(E)\mathscr{L}(E) into EE is continuous and linear, it follows that

(L(π)t)(b)=⟨t,g↦π(g)b⟩=⟨t,IdE∘φ(b)⟩=⟨φ(b)∗t,IdE⟩(Diff. & Anal. Man., R, 13.2.3)=φ(b)∗t. \begin{align*} (L(\pi)t)(b) &= \langle t, g \mapsto \pi(g)b \rangle \\ &= \langle t, \mathrm{Id}_E \circ \varphi(b) \rangle \\ &= \langle \varphi(b)*t, \mathrm{Id}_E \rangle \quad (\text{Diff. \& Anal. Man., R, 13.2.3}) \\ &= \varphi(b)*t. \end{align*}

Finally, φ(b)∗t=t∗εb\varphi(b)*t = t * \varepsilon_b (no. 3, Proposition 14 (ii)).

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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