2
$\begingroup$

Let $\mathfrak{g}$ be the Lie algebra of a Lie group $G$, and $exp:\mathfrak{g}\to G$ be its exponential map. The group $G$ could be finite or infinite dimensional. Let $G$ have the property that

$\bullet$ For each smooth curve $X\in C^{\infty}(\mathbb R,\mathfrak g)$ there exists a curve $g\in C^{\infty}(\mathbb R,G)$ whose right logarithmic derivative is $X$, i.e., $$ g(0) = e, \qquad \partial_t g(t) = T_e(\mu^{g(t)})X(t) = X(t).g(t),\quad\text{where } \mu(a,b)=\mu_a(b)=\mu^b(a) = a.b $$ The curve $g$ is uniquely determined by its initial value $g(0)$, if it exists.

$\bullet$ Put $\operatorname{evol}^r_G(X)=g(1)$ where $g$ is the unique solution required above. Then $\operatorname{evol}^r_G: C^{\infty}(\mathbb R,\mathfrak g)\to G$ is required to be $C^{\infty}$ also.

Note that for $X$ constant in time, $\operatorname{evol}^r_G(X)=\exp(X)$. So each regular Lie group admits an exponential mapping.

My questions are:

1) Is there any expression for the derivative of $\operatorname{evol}^r_G$. It's motivated by the fact that that there's an expression of $(Dexp)_{\mathfrak g}$ using the adjoint action on $\mathfrak g$ and derivative of the left translation in $G$.

2) Can we construct a new Lie group $H\subset = C^{\infty}(\mathbb R,G)$ with Lie algebra $C^{\infty}(\mathbb R,\mathfrak g)$ so that $\operatorname{evol}^r$ becomes the exponential map $C^{\infty}(\mathbb R,\mathfrak g)\to H$?

I must admit that I got the idea of the question from Peter Michor's answer to this question:

Exponential map

$\endgroup$

1 Answer 1

5
$\begingroup$

Answer to 1:

$TG$ is again a Lie group, semidirect product go $G$ over the normal $\mathfrak g$. See 6.7 of here. $TC^\infty(\mathbb R, \mathfrak g) = C^\infty(\mathbb R, \mathfrak g\times \mathfrak g)$. Then $$ T(evol_G^r) = evol^r_{TG}. $$ Be careful with the identifications. This is treated in detail in 38.10 of this book.

Answer to 2:

See 38.11 and 42.21 of this same second book.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.