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Real Group Orbits on Flag Ind-Varieties of SL(∞,C)
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We consider the complex ind-group G = SL(∞,C) and its real forms G0 = SU(∞,∞), SU(p,∞), SL(∞,R), SL(∞,H). Our main object of study are the G0-orbits on an ind-variety G/P for an arbitrary splitting parabolic ind-subgroup P ⊂ G, under the assumption that the subgroups G0 ⊂ G and P ⊂ G are aligned in a natural way. We prove that the intersection of any G0-orbit on G/P with a finite-dimensional flag variety Gn/Pn from a given exhaustion of G / P via Gn/Pn for n → ∞, is a single (G0∩Gn)-orbit. We also characterize all ind-varieties G/P on which there are finitely many G0-orbits, and provide criteria for the existence of open and closed G0-orbits on G/P in the case of infinitely many G0-orbits.
In book
Vol. 191. , Springer, 2016.