We show that any element of the universal Teichm\"uller space is realized by
a unique minimal Lagrangian diffeomorphism from the hyperbolic plane to itself.
The proof uses maximal surfaces in the 3-dimensional anti-de Sitter space. We
show that, in $AdS^{n+1}$, any subset $E$ of the boundary at infinity which is
the boundary at infinity of a space-like hypersurface bounds a maximal
space-like hypersurface. In $AdS^3$, if $E$ is the graph of a quasi-symmetric
homeomorphism, then this maximal surface is unique, and it has negative
sectional curvature.
We consider integrals of type $\int_{O_n}u_{11}^{a_1}...
u_{1n}^{a_n}u_{21}^{b_1}... u_{2n}^{b_n} du$, with respect to the Haar measure
on the orthogonal group. We establish several remarkable invariance properties
satisfied by such integrals, by using combinatorial methods. We present as well
a general formula for such integrals, as a sum of products of factorials.
We consider quasifuchsian manifolds with "particles", i.e., cone
singularities of fixed angle less than $\pi$ going from one connected component
of the boundary at infinity to the other. Each connected component of the
boundary at infinity is then endowed with a conformal structure marked by the
endpoints of the particles. We prove that this defines a homeomorphism from the
space of quasifuchsian metrics with $n$ particles (of fixed angle) and the
product of two copies of the Teichm\"uller space of a surface with $n$ marked
points.
We consider a volume maximization program to construct hyperbolic structures
on triangulated 3-manifolds, for which previous progress has lead to consider
angle assignments which do not correspond to a hyperbolic metric on each
simplex. We show that critical points of the generalized volume are associated
to geometric structures modeled on the extended hyperbolic space -- the natural
extension of hyperbolic space by the de Sitter space -- except for the
degenerate case where all simplices are Euclidean in a generalized sense.