Abstract

We conjecture that the set of homogeneous probability measures on the maximal Satake compactification of an arithmetic locally symmetric space S=Gamma backslash G/K is compact. More precisely, given a sequence of homogeneous probability measures on S, we expect that any weak limit is homogeneous with support contained in precisely one of the boundary components (including S itself). We introduce several tools to study this conjecture and we prove it in a number of cases, including when G={mathbf{SL}}_3({{mathbb {R}}}) and Gamma ={mathbf{SL}}_3({{mathbb {Z}}}).

Highlights

  • 1.1 Background and motivationsThe study of sequences of measures invariant under unipotent flows has been a central theme in homogeneous dynamics, and the deep theorems obtained have had several important arithmetic applications

  • Such that the projection π1 on to the first factor is given by restricting to the corresponding subtorus. It follows that the restriction of (·, ·) to X ∗(AI )Q is a non-degenerate scalar product that is invariant with respect to the action of NMI (AI )(Q)

  • Μ is the homogeneous probability measure on \G associated with a connected algebraic subgroup H of G of type H and an element g ∈ G, and, Hn is contained in H for all n large enough

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Summary

Background and motivations

The study of sequences of measures invariant under unipotent flows has been a central theme in homogeneous dynamics, and the deep theorems obtained have had several important arithmetic applications Prototypical in this respect is Margulis’s proof of the Oppenheim Conjecture concerning the values of irrational indefinite quadratic forms at integral vectors [12]. In [10], building on the earlier work of Dani–Margulis [8], Eskin–Mozes–Shah proved a nondivergence criterion for sequences of homogeneous measures and, motivated by a counting problem for lattice points on homogeneous varieties, applied this to show in [9] that, when, for all n ∈ N, Hn = H, for a fixed reductive subgroup H of G not contained in a proper Q-parabolic subgroup of G, any weak limit μ of μn = μH,gn is homogeneous. This paper deals principally with the convergence of measures on general locally symmetric spaces and their Satake compactifications, but we hope to discuss the Baily–Borel compactification, and possible applications, in a future work

Overview of the results
Borel probability measures
Algebraic groups
Parabolic subgroups
Boundary symmetric spaces
Rational Langlands decomposition
Standard parabolic subgroups
Root systems
Quasi-fundamental weights
2.10 Groups of type H
2.11 Probability measures on homogeneous spaces
The maximal Satake compactification
Main conjecture
Baily–Borel compactification
Relationship between the compactifications
Conjecture for Baily–Borel compactification
The criterion
Groups of Q-rank 0
Groups of Q-rank 1
The case of SL3
A product of modular curves
10 Translates of the Levi of a maximal parabolic subgroup
11 Translates of the unipotent radical of a minimal parabolic
12 Digression on Levi spheres
13 Translates of subgroups of MI by elements of AI

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