Editing Quantum group (section)

==Bicrossproduct quantum groups==
Whereas compact matrix pseudogroups are typically versions of  Drinfeld-Jimbo quantum groups in a dual function algebra formulation, with additional structure, the bicrossproduct ones are a distinct second family of quantum groups of increasing importance as deformations of solvable rather than semisimple Lie groups. They are associated to Lie splittings of Lie algebras or local factorisations of Lie groups and can be viewed as the cross product or Mackey quantisation of one of the factors acting on the other for the algebra and a similar story for the coproduct Δ with the second factor acting back on the first.

The very simplest nontrivial example corresponds to two copies of '''R''' locally acting on each other and results in a quantum group  (given here in an algebraic form) with generators ''p'', ''K'', ''K''<sup>−1</sup>, say, and coproduct

:<math>[p, K]=h K(K-1)</math>
:<math>\Delta p=p\otimes K+1\otimes p</math>
:<math>\Delta K=K\otimes K</math>

where ''h'' is the deformation parameter.

This quantum group was linked to a toy model of Planck scale physics implementing [[Born reciprocity]] when viewed as a deformation of the [[Heisenberg algebra]] of quantum mechanics. Also, starting with any compact real form of a semisimple Lie algebra '''g''' its complexification as a real Lie algebra of twice the dimension splits into '''g''' and a certain solvable Lie algebra (the [[Iwasawa decomposition]]), and this provides a canonical bicrossproduct quantum group associated to '''g'''. For '''su'''(2) one obtains a quantum group deformation of the [[Euclidean group]] E(3) of motions in 3 dimensions.