====== Free bistochastic quantum group ======

The **free bistochastic quantum groups** are the elements of a sequence $(B_N^+)_{N\in \N}$ of [[compact matrix quantum group|compact matrix quantum groups]] introduced by Banica and Speicher in [(:ref:BanSp09)]. Each $B_N^+$ is a [[free_orthogonal_easy_quantum_group|free]] counterpart of the [[bistochastic group]] $B_N$ of the corresponding dimension $N$. 

===== Definition =====
Given $N\in \N$, the **free bistochastic quantum group** $B_N^+$ is the [[compact matrix quantum group]] $(C(B_N^+),u)$ where $u=(u_{i,j})_{i,j=1}^N$ organizes the generators $\{u_{i,j}\}_{i,j=1}^N$ of the (unital) [[wp>Universal_C*-algebra|universal C*-algebra]] 
$$C(B_N^+)\colon\hspace{-0.66em}= C^\ast_1\big\langle\{u_{i,j}\}_{i,j=1}^N\big\,\vert \,u=\overline u,\, uu^t=u^tu=I_N\otimes 1, \, \forall_{i,j=1}^N: {\textstyle\sum_{k=1}^N} u_{i,k}={\textstyle\sum_{l=1}^N} u_{l,j}=1\big\rangle,$$
where $\overline u=(u^\ast_{i,j})_{i,j=1}^N$ is the complex conjugate of $u$ and $u^t=(u_{j,i})_{i,j=1}^N$ the transpose, where $I_N$ is the identity $N\!\times \!N$-matrix and where $1$ is the unit of the universal $C^\ast$-algebra.

The definition can also be expressed by saying that the fundamental corpresentation matrix $u$ of $B_N^+$ is **bistochastic** (or **doubly stochastic**), which is to say that $u$ is orthogonal and each of its rows and columns sums to $1$.

===== Basic Properties =====

The fundamental corepresentation matrix $u$ of $B_N^+$ is in particular //orthogonal//. Hence, $B_N^+$ is a compact quantum subgroup of the [[free orthogonal quantum group]] $O_N^+$.

If $I$ denotes the closed two-sided ideal of $C(B_N^+)$ generated by the relations $u_{i,j}u_{k,l}=u_{k,l}u_{i,j}$ for any $i,j,k,l=1,\ldots, N$, then $C(B_N^+)/I$ is isomorphic to the $C^\ast$-algebra $C(B_N)$ of continuous functions on the [[wp>bistochastic group]] $B_N$, the subgroup of $\mathrm{GL}(N,\C)$ given by all [[wp>doubly stochastic matrix|bistochastic matrices]]. Hence, $B_N^+$ is a compact quantum supergroup of $B_N$.

The free bistochastic quantum groups $(B_N^+)_{N\in \N}$ are an [[easy_quantum_group|easy]] family of compact matrix quantum groups, i.e., the intertwiner spaces of their corepresentation categories are induced by a [[category of partitions]]. More precisely, it is the [[category of all non-crossing partitions with small blocks]] that induces the corepresentation categories of $(S_N^+)_{N\in \N}$. Its canonical generating partition is $\singleton$. 


===== Representation theory =====


===== Cohomology =====


===== Related quantum groups =====

===== References =====

[( :ref:BanSp09 >>
author:  Banica, Teodor and Speicher, Roland
title:   Liberation of orthogonal Lie groups
year:    2009
journal: Advances in Mathematics
volume:  222
issue:   4
pages:   1461--150
url:     https://doi.org/10.1016/j.aim.2009.06.009
archivePrefix: arXiv
eprint   :0808.2628
)]