We define naturally Hermite-Lorentz metrics on almost-complex manifolds as special case of pseudo-Riemannian metrics compatible with the almost complex structure. We study their isometry groups.

Remark. The word generic cannot be replaced by all. We show this in Example 6. Theorem 1 is proven first for complex groups then deduced for real groups. It is not known at this time, to the author, whether or not these results hold true for more general algebraic groups. Our proof exploits Weyl’s Unitarian Trick. Before proving this theorem, we present some corollaries to demonstrate its value...

For a (compact) subset K of a metric space and ε > 0, the covering number N(K, ε) is defined as the smallest number of balls of radius ε whose union covers K. Knowledge of the metric entropy, i.e., the asymptotic behaviour of covering numbers for (families of) metric spaces is important in many areas of mathematics (geometry, functional analysis, probability, coding theory, to name a few). In t...

This article is an expository paper. We first survey developments over the past three decades in the theory of harmonic analysis on reductive symmetric spaces. Next we deal with the particular homogeneous space of non-reductive type, the so called Siegel-Jacobi space that is important arithmetically and geometrically. We present some new results on the Siegel-Jacobi space.

Motivated by inhomogeneous scaling of left invariant Riemannian metrics on a Lie group G, we consider a family of stochastic differential equations (SDEs) on G with Markov operators L = 1 ∑ k(Ak) 2 + 1 A0 + Y0, where > 0, {Ak} generates a sub Lie-algebra h of the Lie algebra g, and Y0 ∈ g. Assuming that G/H is a reductive homogeneous space, in the sense of Nomizu, we take → 0 and study the asym...

The solution of the eigenvalue problem of the Laplacian on a general homogeneous space G/H is given. Here G is a compact, semi-simple Lie group, H is a closed subgroup of G, and the rank of H is equal to the rank of G. It is shown that the multiplicity of the lowest eigenvalue of the Laplacian on G/H is just the degeneracy of the lowest Landau level for a particle moving on G/H in the presence ...

We consider a connected, locally compact topological space X. We suppose that a pseudo-distance d is defined on X that is, d : X × X 7−→ R+ such that d (x, y) > 0 if and only if x 6= y; d (x, y) = d (y, x) ; d (x, z) ≤ γ [d (x, y) + d (y, z)] for all x, y, z ∈ X, where γ ≥ 1 is some given constant and we suppose that the pseudo-balls B (x, r) = {y ∈ X : d (x, y) < r} , r > 0, form a basis of op...

Let G be a semi-simple Lie group with finite center and S ⊂ G a semigroup with intS 6= Ø . A closed subgroup L ⊂ G is said to be S -admissible if S is transitive in G/L . In [10] it was proved that a necessary condition for L to be S -admissible is that its action in B (S) is minimal and contractive where B (S) is the flag manifold associated with S , as in [9]. It is proved here, under an addi...

Let G be a compact, semi-simple Lie group and H a maximal rank reductive subgroup. The irreducible representations of G can be constructed as spaces of harmonic spinors with respect to a Dirac operator on the homogeneous space G/H twisted by bundles associated to the irreducible, possibly projective, representations of H. Here, we give a quick proof of this result, computing the index and kerne...