# nLab ALE space

Contents

### Context

#### Riemannian geometry

Riemannian geometry

# Contents

## Idea

An almost locally Euclidean space or ALE space for short is a solution to the Euclidean Einstein equations which is a blow-up of an ADE-orbifold singularity $\mathbb{C}^2/\Gamma$ for finite subgroup $\Gamma \hookrightarrow SU(2)$.

geometry transverse to KK-monopolesRiemannian metricremarks
Taub-NUT space:
geometry transverse to
$N+1$ distinct KK-monopoles
at $\vec r_i \in \mathbb{R}^3 \;\; i \in \{1, \cdots, N+1\}$
$\array{d s^2_{TaubNUT} \coloneqq U^{-1}(d x^4 + \vec \omega \cdot d \vec r)^2 + U (d \vec r)^2 \,, \\ \vec r \in \mathbb{R}^3,\, x^4 \in \mathbb{R}/(2 \pi R\mathbb{Z}) \\ U \coloneqq 1 + \underoverset{i = 1}{N+1}{\sum} U_i\,, \phantom{AA} \vec \omega \coloneqq \underoverset{i = 1}{N+1}{\sum} \vec \omega_i \\ U_i \coloneqq \frac{R/2}{ {\vert \vec r - \vec r_i\vert} }\,, \phantom{AA} \vec \nabla \times \vec \omega= \vec \nabla U_i}$(e.g. Sen 97b, Sect. 2)
ALE space
Taub-NUT close to $N$ close-by KK-monopoles
e.g. close to $\vec r = 0$: $\frac{{\vert \vec r_i\vert}}{R/2}, \frac{{\vert \vec r\vert}}{R/2} \ll 1$
$\array{d s^2_{ALE} \coloneqq U'^{-1}(d x^4 + \vec \omega \cdot d \vec r)^2 + U' (d \vec r)^2 \,, \\ \vec r \in \mathbb{R}^3,\, x^4 \in \mathbb{R}/(2 \pi R\mathbb{Z}) \\ U' \coloneqq \underoverset{i = 1}{N+1}{\sum} U'_i\,, \phantom{AA} \vec \omega \coloneqq \underoverset{i = 1}{N+1}{\sum} \vec \omega_i \\ U'_i \coloneqq \frac{R/2}{ {\vert \vec r - \vec r_i\vert} }\,, \phantom{AA} \vec \nabla \times \vec \omega= \vec \nabla U_i}$e.g. via Euler angles: $\vec \omega = (N+1)R/2(\cos(\theta)-1) d\psi$
(e.g. Asano 00, Sect. 2)
$A_N$-type ADE singularity:
ALE space in the limit
where all $N+1$ KK-monopoles coincide at $vec r_i = 0$
$\array{d s^2_{A_N Sing} \coloneqq \frac{\vert\vec r\vert }{(N+1)R/2}(d x^4 + \vec \omega \cdot d \vec r)^2 + \frac{ (N+1)R/2}{\vert \vec r\vert} (d \vec r)^2 \,, \\ \vec r \in \mathbb{R}^3,\, x^4 \in \mathbb{R}/(2 \pi R\mathbb{Z}) }$(e.g. Asano 00, Sect. 3)

## References

An ADE classification of 4d ALE-spaces is due to

• Peter Kronheimer, The construction of ALE spaces as hyper-Kähler quotients, J. Differential Geom. Volume 29, Number 3 (1989), 665-683. (Euclid)

In

this result is interpreted physically as describing the moduli space of vacua of gauge theories with spontaneously broken symmetry (“Higgs branches”). See at 3d mirror symmetry for more on this.

For application in string theory see at KK-monopole and see

Last revised on March 19, 2019 at 06:58:40. See the history of this page for a list of all contributions to it.