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A. Vershik

Publications and source records attributed to A. Vershik.

At least 37 records · Page 2Linked to original sources
arXiv2016

On the relation of some combinatorial functions to representation theory

The paper is devoted to the study of some well-knonw combinatorial functions on the symmetric group $\sn$ --- the major index $\maj$, the descent number $\des$, and the inversion number $\inv$ --- from the representation-theoretic point of view. We show that each of these functions generates in the group algebra the same ideal, and the restriction of the left regular representation to this ideal is isomorphic to the representation of $\sn$ in the space of $n\times n$ skew-symmetric matrices. This allows us to obtain formulas for the functions $\maj,\des,\inv$ in terms of matrices of an exceptionally simple form. These formulas are applied to find the spectra of the elements under study in the regular representation, as well as to deduce a series of identities relating these functions to one another and to the number of fixed points $\fix$. \smallskip\noindent {\it Keywords:} major index, descent number, inversion number, representations of the symmetric group, skew-symmetric matrices, dual complexity.

math.RT↗
arXiv2016

Asymptotic theory of path spaces of graded graphs and its applications

The survey covers several topics related to the asymptotic structure of various combinatorial and analytic objects such as the path spaces in graded graphs (Bratteli diagrams), invariant measures with respect to countable groups, etc. The main subject is the asymptotic structure of filtrations and a new notion of standardness. All graded graphs and all filtrations of Borel or measure spaces can be divided into two classes: the standard ones, which have a regular behavior at infinity, and the other ones. Depending on this property, the list of invariant measures can either be well parameterized or have no good parametrization at all. One of the main results is a general standardness criterion for filtrations. We consider some old and new examples which illustrate the usefulness of this point of view and the breadth of its applications.

math.DS↗
arXiv2015

On the classification problem of matrix distributions of measurable functions in several variables

We resume the results from \cite{Vershik FA} on the classification of measurable functions in several variables, with some minor corrections of purely technical nature, and give a partial solution to the characterization problem of so--called matrix distributions, which are the metric invariants of measurable functions introduced in \cite{Vershik FA}. The characterization of these invariants of the ergodic measures on the space of matrices is closely related to Aldous' and Hoover's representation of row-- and column--exchangable distributions \cite{Aldous1981,Hoover1982}, but not in such an obvious way as was initially expected in \cite{Vershik FA}.

math.PR↗
arXiv2015

Phase transition in the exit boundary problem for random walks on groups

We describe the full exit boundary of random walks on homogeneous trees, in particular, on the free groups. This model exhibits a phase transition, namely, the family of Markov measures under study loses ergodicity as a parameter of the random walk changes. The problem under consideration is a special case of the problem of describing the invariant (central) measures on branching graphs, which covers a number of problems in combinatorics, representation theory, probability and was fully stated in a series of recent papers by the first author \cite{V1,V2,V3}. On the other hand, in the context of the theory of Markov processes, close problems were discussed as early as 1960s by E.~B.~Dynkin.

math.PR↗
arXiv2015

Equipped graded graphs, projective limits of simplices, and their boundaries

In this paper, we develop a theory of equipped graded graphs (or Bratteli diagrams) and an alternative theory of projective limits of finite-dimensional simplices. An equipment is an additional structure on the graph, namely, a system of "cotransition" probabilities on the set of its paths. The main problem is to describe all probability measures on the path space of a graph with given cotransition probabilities; it goes back to the problem, posed by E.~B.~Dynkin in the 1960s, of describing exit and entrance boundaries for Markov chains. The most important example is the problem of describing all central measures, to which one can reduce the problems of describing states on AF-algebras or characters on locally finite groups. We suggest an unification of the whole theory, an interpretation of the notions of Martin, Choquet, and Dynkin boundaries in terms of equipped graded graphs and in terms of the theory of projective limits of simplices. In the last section, we study the new notion of "standardness" of projective limits of simplices and of equipped Bratteli diagrams, as well as the notion of "lacunarization."

math.FA↗
arXiv2014

The serpentine representation of the infinite symmetric group and the basic representation of the affine Lie algebra $\widehat{\mathfrak{sl}_2}$

We introduce and study the so-called serpentine representations of the infinite symmetric group $\sinf$, which turn out to be closely related to the basic representation of the affine Lie algebra $\widehat{\mathfrak{sl}_2}$ and representations of the Virasoro algebra. This is a new version of the manuscript of the same authors "On a relation between the basic representation of the affine Lie algebra $\widehat\sl$ and a Schur--Weyl representation of the infinite symmetric group" (arXiv:1403.1558)

math.RT↗
arXiv2014

Laplace operators in gamma analysis

Let $\mathbb K(\mathbb R^d)$ denote the cone of discrete Radon measures on $\mathbb R^d$. The gamma measure $\mathcal G$ is the probability measure on $\mathbb K(\mathbb R^d)$ which is a measure-valued Lévy process with intensity measure $s^{-1}e^{-s}\,ds$ on $(0,\infty)$. We study a class of Laplace-type operators in $L^2(\mathbb K(\mathbb R^d),\mathcal G)$. These operators are defined as generators of certain (local) Dirichlet forms. The main result of the papers is the essential self-adjointness of these operators on a set of `test' cylinder functions on $\mathbb K(\mathbb R^d)$.

math.PR↗
arXiv2014

Virtual Continuity of Measurable Functions and Its Applications

Classical theorem of Luzin states that a measurable function of one real variable is "almost" continuous. For measurable functions of several variables the analogous statement (continuity on the product of sets having almost full measure) does not hold in general. Searching for a right analogue of Luzin theorem leads to a notion of virtually continuous functions of several variables. This probably new notion implicitly appears in the statements of embedding theorems and trace theorems for Sobolev spaces. In fact it reveals the nature of such theorems as statements about virtual continuity. Our results imply that under conditions of Sobolev theorems there is a well-defined integration of a function over wide class of singular measures, including the measures concentrated on submanifolds. The notion of virtual continuity is used also for the classification of measurable functions of several variables and in some questions on dynamical systems, theory of polymorphisms and bistochastic measures. In this paper we recall necessary definitions and properties of admissible metrics, give several definitions of virtual continuity and discuss some applications. Revised version (without the proofs) is published in \cite{VZPFA}.

math.FA↗
arXiv2013

On classification of measurable functions of several variables

We define a normal form (called the canonical image) of an arbitrary measurable function of several variables with respect to a natural group of transformations; describe a new complete system of invariants of such a function (the system of joint distributions); and relate these notions to the matrix distribution, another invariant of measurable functions found earlier, which is a random matrix. Bibliography: 7 titles.

math.DS↗
arXiv2012

Geometry and Dynamics of Admissible Metrics in Measure Spaces

We study a wide class of metrics in a Lebesgue space with a standard measure, the class of so-called admissible metrics. We consider the cone of admissible metrics, introduce a special norm in it, prove compactness criteria, define the "-entropy of a measure space with an admissible metric, etc. These notions and related results are applied to the theory of transformations with invariant measure; namely, we study the asymptotic properties of orbits in the cone of admissible metrics with respect to a given transformation or a group of transformations. The main result of this paper is a new discreteness criterion for the spectrum of an ergodic transformation: we prove that the spectrum is discrete if and only if the "-entropy of the averages of some (and hence any) admissible metric over fragments of its trajectory is uniformly bounded.

math.DS↗
arXiv2012

Infnite-dimensional Schur-Weyl duality and the Coxeter-Laplace operator

We extend the classical Schur-Weyl duality between representations of the groups $SL(n,\C)$ and $\sN$ to the case of $SL(n,\C)$ and the infinite symmetric group $\sinf$. Our construction is based on a "dynamic," or inductive, scheme of Schur-Weyl dualities. It leads to a new class of representations of the infinite symmetric group, which have not appeared earlier. We describe these representations and, in particular, find their spectral types with respect to the Gelfand-Tsetlin algebra. The main example of such a representation acts in an incomplete infinite tensor product. As an important application, we consider the weak limit of the so-called Coxeter-Laplace operator, which is essentially the Hamiltonian of the XXX Heisenberg model, in these representations.

math.RT↗
arXiv2012

Stable states and representations of the infnite symmetric group

We introduce the notion of stable representations, -- it is a new class of the representations of a certain class of groups which defined with positive definite functions which generalize the classical notion of the characters (or trace). We give the complete description of this class for infinite symmetric group ${\frak S}_{\Bbb N}$. It happened the family of the stable representations of ${\frak S}_{\Bbb N}$ coincides with the set of representations of the components (left or right) of the admissible representations of the double-group in the sense of Ol'shanski. In particular all these are representation of type ${\rm II}$ which was open question for many years.

math.FA↗
arXiv2011

The Pascal automorphism has a purely continuous spectrum

We give the detale description from various points of view of Pascal automorphism,--- a natural transformation of the space of paths in the Pascal graph (= infinite Pascal triangle), and describetha plan of the proof of continuiuty of its spectrum. If we realize this automorphism as the shift in the space of 0-1 sequences, we obtain a stationary measure, called the Pascal measure, whose properties we study. The transformations generated by classical graded graphs, such as the ordinary and multidimensional Pascal graphs, the Young graph, the graph of walks in Weyl chambers, etc., provide examples of combinatorial nature from a new and very interesting class of adic transformations introduced as early as in \cite{V81}; some considerations by V. I. Arnold also lead to such transformations. We discuss problems arising in this field. This is the first paper of the series of articles about adic transformations.

math.DS↗
arXiv2011

Scaling entropy and automorphisms with purely point spectrum

We study the dynamics of the metrics generated by measure preserving transformations. We consider a sequence of average metrics and define the corresponding sequence of $ε$-entropies ({\it scaling sequence}) of the measure with respect to the mean metrics. The main result claims that scaling sequences of an automorphism with respect to any {\it admissible metric} is bounded if and only if the automorphism has discrete spectrum. This gives a non-spectral criterion of the discreteness of the spectrum of an automorphism. The related result was discussed in \cite{Fe} but our approach is different. This article is one in the series of papers about asymptotic theory of sequences of the metric compacts with measure and its role in dynamics.

math.DS↗
arXiv2010

Nonfree Actions of Countable Groups and their Characters

We introduce the definition of totally nonfree actions of groups; such actions are naturally related to the theory of characters of groups and their factor-representations of type II. This short note is a brief exposition of a part of a more detailed paper on this subject, which is now in preparation.

math.DS↗
arXiv2010

Dynamics of metrics in measure spaces and their asymptotic invariants

We discuss the Kolmogorov's entropy and Sinai's definition of it; and then define a deformation of the entropy, called {\it scaling entropy}; this is also a metric invariant of the measure preserving actions of the group, which is more powerful than the ordinary entropy. To define it, we involve the notion of the $ε$-entropy of a metric in a measure space, also suggested by A. N. Kolmogorov slightly earlier. We suggest to replace the techniques of measurable partitions, conventional in entropy theory, by that of iterations of metrics or semi-metrics. This leads us to the key idea of this paper which as we hope is the answer on the old question: what is the natural context in which one should consider the entropy of measure-preserving actions of groups? the same question about its generalizations--scaling entropy, and more general problems of ergodic theory. Namely, we propose a certain research program, called {\it asymptotic dynamics of metrics in a measure space}, in which, for instance, the generalized entropy is understood as {\it the asymptotic Hausdorff dimension of a sequence of metric spaces associated with dynamical system.} As may be supposed, the metric isomorphism problem for dynamical systems as a whole also gets a new geometric interpretation.

math.DS↗
arXiv2009

Rational approximation of the maximal commutative subgroups of GL(n,R)

How to find "best rational approximations" of maximal commutative subgroups of GL(n,R)? In this paper we pose and make first steps in the study of this problem. It contains both classical problems of Diophantine and simultaneous approximations as a particular subcases but in general is much wider. We prove estimates for n=2 for both totaly real and complex cases and write the algorithm to construct best approximations of a fixed size. In addition we introduce a relation between best approximations and sails of cones and interpret the result for totally real subgroups in geometric terms of sails.

math.NT↗