5,016 research outputs found
Equilibrium states for non-uniformly expanding maps: decay of correlations and strong stability
We study the rate of decay of correlations for equilibrium states associated
to a robust class of non-uniformly expanding maps where no Markov assumption is
required. We show that the Ruelle-Perron-Frobenius operator acting on the space
of Holder continuous observables has a spectral gap and deduce the exponential
decay of correlations and the central limit theorem. In particular, we obtain
an alternative proof for the existence and uniqueness of the equilibrium states
and we prove that the topological pressure varies continuously. Finally, we use
the spectral properties of the transfer operators in space of differentiable
observables to obtain strong stability results under deterministic and random
perturbations.Comment: 29 pages, Annales de l'Institut Henri Poincare - Analyse non lineaire
(to appear
Groups of given intermediate word growth
We show that there exists a finitely generated group of growth ~f for all
functions f:\mathbb{R}\rightarrow\mathbb{R} satisfying f(2R) \leq f(R)^{2} \leq
f(\eta R) for all R large enough and \eta\approx2.4675 the positive root of
X^{3}-X^{2}-2X-4. This covers all functions that grow uniformly faster than
\exp(R^{\log2/\log\eta}).
We also give a family of self-similar branched groups of growth
~\exp(R^\alpha) for a dense set of \alpha\in(\log2/\log\eta,1).Comment: small typos corrected from v
The cycle contraction mapping theorem
This report lays the foundation for a theory of total correctness for programs not based upon termination. The Cycle Contraction Mapping Theorem is both an extension of Wadge's cycle sum theorem for Kahn data flow and a generalisation of Banach's contraction mapping theorem to a class of quasi metric spaces definable using the symmetric Partial Metric distance function. This work provides considerable evidence that it is possible after all to construct a metric theory for Scott style partial order domains
Curvature in Noncommutative Geometry
Our understanding of the notion of curvature in a noncommutative setting has
progressed substantially in the past ten years. This new episode in
noncommutative geometry started when a Gauss-Bonnet theorem was proved by
Connes and Tretkoff for a curved noncommutative two torus. Ideas from spectral
geometry and heat kernel asymptotic expansions suggest a general way of
defining local curvature invariants for noncommutative Riemannian type spaces
where the metric structure is encoded by a Dirac type operator. To carry
explicit computations however one needs quite intriguing new ideas. We give an
account of the most recent developments on the notion of curvature in
noncommutative geometry in this paper.Comment: 76 pages, 8 figures, final version, one section on open problems
added, and references expanded. Appears in "Advances in Noncommutative
Geometry - on the occasion of Alain Connes' 70th birthday
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