We prove that we have an isomorphism of type $A_{aut}(\mathbb
C_\sigma[G])\simeq A_{aut}(\mathbb C[G])^\sigma$, for any finite group $G$, and
any 2-cocycle $\sigma$ on $G$. In the particular case $G=\mathbb Z_n^2$, this
leads to a Haar-measure preserving identification between the subalgebra of
$A_o(n)$ generated by the variables $u_{ij}^2$, and the subalgebra of
$A_s(n^2)$ generated by the variables $X_{ij}=\sum_{a,b=1}^np_{ia,jb}$.
The half-liberated orthogonal group $O_n^*$ appears as intermediate quantum
group between the orthogonal group $O_n$, and its free version $O_n^+$. We
discuss here its basic algebraic properties, and we classify its irreducible
representations. The classification of representations is done by using a
certain twisting-type relation between $O_n^*$ and $U_n$, a non abelian
discrete group playing the role of weight lattice for $O_n^*$, and a number of
methods inspired from the theory of Lie algebras.
The half-liberated orthogonal group $O_n^*$ appears as intermediate quantum
group between the orthogonal group $O_n$, and its free version $O_n^+$. We
discuss here its basic algebraic properties, and we classify its irreducible
representations. The classification of representations is done by using a
certain twisting-type relation between $O_n^*$ and $U_n$, a non abelian
discrete group playing the role of weight lattice for $O_n^*$, and a number of
methods inspired from the theory of Lie algebras.
We consider integrals of type $\int_{O_n}u_{11}^{a_1}...
u_{1n}^{a_n}u_{21}^{b_1}... u_{2n}^{b_n} du$, with respect to the Haar measure
on the orthogonal group. We establish several remarkable invariance properties
satisfied by such integrals, by using combinatorial methods. We present as well
a general formula for such integrals, as a sum of products of factorials.
We consider several orthogonal quantum groups satisfying the easiness
assumption axiomatized in our previous paper. For each of them we discuss the
computation of the asymptotic law of Tr(u^k) with respect to the Haar measure,
u being the fundamental representation. For the classical groups O_n, S_n we
recover in this way some well-known results of Diaconis and Shahshahani.
We consider several orthogonal quantum groups satisfying the easiness
assumption axiomatized in our previous paper. For each of them we discuss the
computation of the asymptotic law of Tr(u^k) with respect to the Haar measure,
u being the fundamental representation. For the classical groups O_n, S_n we
recover in this way some well-known results of Diaconis and Shahshahani.