Marches aléatoires sur les espaces homogènes
Marches aléatoires sur les espaces homogènes des groupes nilpotents connexes à génération compacte
Maximal degenerate representations of SL.
Maximal functions related to subelliptic operators invariant under an action of a nilpotent Lie group
Maximal functions related to subelliptic operators invariant under an action of a solvable Lie group
On the domain S_a = {(x,e^b): x ∈ N, b ∈ ℝ, b > a} where N is a simply connected nilpotent Lie group, a certain N-left-invariant, second order, degenerate elliptic operator L is considered. N × {e^a} is the Poisson boundary for L-harmonic functions F, i.e. F is the Poisson integral F(xe^b) = ʃ_N f(xy)dμ^b_a(x), for an f in L^∞(N). The main theorem of the paper asserts that the maximal function M^a f(x) = sup{|ʃf(xy)dμ_a^b(y)| : b > a} is of weak type (1,1).
Maximal functions related to subelliptic operators with polynomially growing coefficients.
Minimality and unique ergodicity for subgroup actions
Let be an -algebraic semisimple group, an algebraic -subgroup, and a lattice in . Partially answering a question posed by Hillel Furstenberg in 1972, we prove that if the action of on is minimal, then it is uniquely ergodic. Our proof uses in an essential way Marina Ratner’s classification of probability measures on invariant under unipotent elements, and the study of “tubes” in .
Monotone functions on symmetric spaces.
Moser-Trudinger and logarithmic HLS inequalities for systems
We prove several optimal Moser–Trudinger and logarithmic Hardy–Littlewood–Sobolev inequalities for systems in two dimensions. These include inequalities on the sphere , on a bounded domain and on all of . In some cases we also address the question of existence of minimizers.
Multiplicité un pour les espaces symétriques exponentiels