Duflo's branching and moment-map conjecture for discrete series

Let GG be a real almost algebraic group, let π\pi be a discrete series representation attached to a coadjoint orbit Oπ\mathcal{O}_{\pi}, and let HH be a closed almost algebraic subgroup. Let

q ⁣:Oπhq\colon \mathcal{O}_{\pi}\rightarrow \mathfrak{h}^{\ast}

be the moment map. Duflo's conjecture. (i) The restriction πH\pi\vert_{H} is HH-admissible if and only if qq is weakly proper. (ii) If πH\pi\vert_{H} is HH-admissible, every irreducible HH-representation σ\sigma appearing in it is attached to a strongly regular HH-coadjoint orbit Oσ\mathcal{O}'_{\sigma} contained in q(Oπ)q(\mathcal{O}_{\pi}). (iii) If πH\pi\vert_{H} is HH-admissible, the multiplicity of each such σ\sigma can be expressed geometrically in terms of the reduced space q1(Oσ)/Hq^{-1}(\mathcal{O}'_{\sigma})/H. This conjecture connects branching laws with the geometry of moment maps and is motivated by the orbit method and quantization-commutes-with-reduction. The paper verifies it for G=Spin(N,1)G=\operatorname{Spin}(N,1) and parabolic subgroups, while the general statement remains open.

Sources & referencesView supporting material

Primary source

Gang Liu, Yoshiki Oshima and Jun Yu, “Restriction of irreducible unitary representations of Spin(N,1) to parabolic subgroups”, arXiv:2010.01026 (2021).

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