Type-II spectral decomposition conjecture for standard quotients

Let (G,H,L)(G,H,L) be a properly transitive triple. Write G^H\widehat G_H for the relevant HH-cospherical GG-representations, let D(G/H)^\widehat{\mathbf D(G/H)} denote the joint spectrum of D(G/H)\mathbf D(G/H), and let VπV_\pi be a representation of LL.

Type-II spectral decomposition conjecture. There exist a topological space G^HLG^H\widehat G_H^L\supset\widehat G_H, a continuous finite-to-one map

p:G^HLD(G/H)^,p:\widehat G_H^L\longrightarrow \widehat{\mathbf D(G/H)},

measurable Hilbert-space fibers [HomL(Wρ,,Vπ,)(Wρ,)H]0[\operatorname{Hom}_L(W_{\rho,\infty},V_{\pi,\infty})\otimes(W_{\rho,-\infty})^H]_0, and a σ\sigma-finite Borel measure μπ\mu_\pi such that, for every πL^\pi\in\widehat L with VπLH{0}V_\pi^{L\cap H}\ne\{0\}, the natural D(G/H)\mathbf D(G/H)-equivariant maps induce a unitary equivalence

VπLHG^HL[HomL(Wρ,,Vπ,)(Wρ,)H]0dμπ(ρ).V_\pi^{L\cap H}\cong\int^{\oplus}_{\widehat G_H^L}[\operatorname{Hom}_L(W_{\rho,\infty},V_{\pi,\infty})\otimes(W_{\rho,-\infty})^H]_0\,d\mu_\pi(\rho).

This is intended to supply the missing spectral decomposition for standard quotients associated with Type-II triples, independently of the lattice Γ\Gamma. The source presents it as a conjecture and gives no resolution status.

Sources & referencesView supporting material

Primary source

Salah Mehdi and Martin Olbrich, “Harmonic analysis on compact standard quotients of non-Riemannian semisimple symmetric spaces”, arXiv:2607.25528 (2026).

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