# Contents

## Idea

The orthogonal group $O(n,n)$ for signature $(n,n)$ is sometimes called the Narain group or generalized T-duality group for the role that it plays in T-duality of type II string theory. See also at type II geometry.

## Properties

### Structure group of generalized tangent bundle

For $X$ a smooth manifold, the generalized tangent bundle $T X \oplus T^* X$ has as structure group the Narain group.

### Maximal compact subgroup

The maximal compact subgroup of the Narain group is the product group $O(n) \times O(n)$. A reduction of the structure group of the generalized tangent bundle along the inclusion defines a type II geometry.

groupsymboluniversal coversymbolhigher coversymbol
orthogonal group$\mathrm{O}(n)$Pin group$Pin(n)$Tring group$Tring(n)$
special orthogonal group$SO(n)$Spin group$Spin(n)$String group$String(n)$
Lorentz group$\mathrm{O}(n,1)$$\,$$Spin(n,1)$$\,$$\,$
anti de Sitter group$\mathrm{O}(n,2)$$\,$$Spin(n,2)$$\,$$\,$
Narain group$O(n,n)$
Poincaré group$ISO(n,1)$$\,$$\,$$\,$$\,$
super Poincaré group$sISO(n,1)$$\,$$\,$$\,$$\,$
Created on May 28, 2012 01:47:29 by Urs Schreiber (82.113.99.74)