# AdS Poisson homogeneous spaces and Drinfel'd doubles

## TL;DR

This paper explores the structure of Poisson homogeneous spaces related to Drinfel'd doubles, providing explicit descriptions for spaces like AdS3 and hyperbolic space, and classifying their Poisson structures.

## Contribution

It offers a detailed analysis of Poisson homogeneous spaces over classical doubles, including explicit classifications for AdS3 and hyperbolic spaces, and connects these to Drinfel'd double structures.

## Key findings

- Explicit descriptions of 2D Poisson homogeneous spaces over SL(2,R)
- Classification of Poisson structures on AdS3 from Drinfel'd doubles
- Identification of two Poisson homogeneous structures on AdS3

## Abstract

The correspondence between Poisson homogeneous spaces over a Poisson-Lie group $G$ and Lagrangian Lie subalgebras of the classical double $D({\mathfrak g})$ is revisited and explored in detail for the case in which ${\mathfrak g}=D(\mathfrak a)$ is a classical double itself. We apply these results to give an explicit description of some coisotropic 2d Poisson homogeneous spaces over the group $\mathrm{SL}(2,R)\cong\mathrm{SO}(2,1)$, namely 2d anti de Sitter space, 2d hyperbolic space and the lightcone in 3d Minkowski space. We show how each of these spaces is obtained as a quotient with respect to a Poisson-subgroup for one of the three inequivalent Lie bialgebra structures on ${sl}(2,R)$ and as a coisotropic one for the others. We then construct families of coisotropic Poisson homogeneous structures for 3d anti de Sitter space $\mathrm{AdS}_3$ and show that the ones that are quotients by a Poisson subgroup are determined by a three-parameter family of classical $r$-matrices for ${so}(2,2)$, while the non Poisson-subgroup cases are much more numerous. In particular, we present the two Poisson homogeneous structures on $\mathrm{AdS}_3$ that arise from two Drinfel'd double structures on $\mathrm{SO}(2,2)$. The first one realises $\mathrm{AdS}_3$ as a quotient of $\mathrm{SO}(2,2)$ by the Poisson-subgroup $\mathrm{SL}(2,R)$, while the second one, the non-commutative spacetime of the twisted $\kappa$-AdS deformation, realises $\mathrm{AdS}_3$ as a coisotropic Poisson homogeneous space.