39,280 research outputs found
The classical r-matrix method for nonlinear sigma-model
The canonical Poisson structure of nonlinear sigma-model is presented as a
Lie-Poisson r-matrix bracket on coadjoint orbits. It is shown that the Poisson
structure of this model is determined by some `hidden singularities' of the Lax
matrix.Comment: 18 pages, LaTe
Symmetric measures via moments
Algebraic tools in statistics have recently been receiving special attention
and a number of interactions between algebraic geometry and computational
statistics have been rapidly developing. This paper presents another such
connection, namely, one between probabilistic models invariant under a finite
group of (non-singular) linear transformations and polynomials invariant under
the same group. Two specific aspects of the connection are discussed:
generalization of the (uniqueness part of the multivariate) problem of moments
and log-linear, or toric, modeling by expansion of invariant terms. A
distribution of minuscule subimages extracted from a large database of natural
images is analyzed to illustrate the above concepts.Comment: Published in at http://dx.doi.org/10.3150/07-BEJ6144 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
On density of horospheres in dynamical laminations
In 1985 D.Sullivan had introduced a dictionary between two domains of complex
dynamics: iterations of rational functions on the Riemann sphere and Kleinian
groups. The latters are discrete subgroups of the group of conformal
automorphisms of the Riemann sphere. This dictionary motivated many remarkable
results in both domains, starting from the famous Sullivan's no wandering
domain theorem in the theory of iterations of rational functions.
One of the principal objects used in the study of Kleinian groups is the
hyperbolic 3- manifold associated to a Kleinian group, which is the quotient of
its lifted action to the hyperbolic 3- space. M.Lyubich and Y.Minsky have
suggested to extend Sullivan's dictionary by providing an analogous
construction for iterations of rational functions. Namely, they have
constructed a lamination by three-dimensional manifolds equipped with a
continuous family with hyperbolic metrics on them (may be with singularities).
The action of the rational mapping on the sphere lifts naturally up to
homeomorphic action on the hyperbolic lamination that is isometric along the
leaves. The action on the hyperbolic lamination admits a well-defined quotient
called {\it the quotient hyperbolic lamination}.
We study the arrangement of the horospheres in the quotient hyperbolic
lamination. The main result says that if a rational function does not belong to
a small list of exceptions (powers, Chebyshev and Latt\`es), then there are
many dense horospheres, i.e., the horospheric lamination is
topologically-transitive. We show that for "many" rational functions
(hyperbolic or critically-nonrecurrent nonparabolic) the quotient horospheric
lamination is minimal: each horosphere is dense.Comment: The complete versio
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