Stably Cayley semisimple groups
  A linear algebraic group G over a field k is called a Cayley group if it admits a Cayley map, i.e. a G-equivariant birational isomorphism over k between the group variety G and its Lie algebra Lie(G). A prototypical example is the classical "Cayley transform" for the special orthogonal group SO(n) defined by Arthur Cayley in 1846. A linear algebraic k-group G is called stably Cayley if $G \times S$ is Cayley for some split k-torus S. We classify stably Cayley semisimple groups over an arbitrary field k of characteristic 0. 
Mikhail Borovoi and Boris Kunyavskii
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