@article {2006,
title = {A Hopf bundle over a quantum four-sphere from the symplectic group},
journal = {Commun. Math. Phys. 263 (2006) 65-88},
number = {arXiv.org;math/0407342v2},
year = {2006},
abstract = {We construct a quantum version of the SU(2) Hopf bundle $S^7 \\\\to S^4$. The quantum sphere $S^7_q$ arises from the symplectic group $Sp_q(2)$ and a quantum 4-sphere $S^4_q$ is obtained via a suitable self-adjoint idempotent $p$ whose entries generate the algebra $A(S^4_q)$ of polynomial functions over it. This projection determines a deformation of an (anti-)instanton bundle over the classical sphere $S^4$. We compute the fundamental $K$-homology class of $S^4_q$ and pair it with the class of $p$ in the $K$-theory getting the value -1 for the topological charge. There is a right coaction of $SU_q(2)$ on $S^7_q$ such that the algebra $A(S^7_q)$ is a non trivial quantum principal bundle over $A(S^4_q)$ with structure quantum group $A(SU_q(2))$.},
doi = {10.1007/s00220-005-1494-3},
url = {http://hdl.handle.net/1963/2179},
author = {Giovanni Landi and Chiara Pagani and Cesare Reina}
}