Pseudocharacters on free groups, invariant with respect to some types of endomorphisms

We investigate methods for constructing nontrivial pseudocharacters on a free group F _n invariant with respect to certain types of endomorphisms. We find some conditions for endomorphisms of the free group under which there is a nontrivial pseudocharacter that is invariant with respect to these endomorphisms. We consider free products $ R = \tilde{R}*\prod\limits_{{i = k}}^n {\left\langle {{r_i}} \right\rangle } $ , where one factor is F _n , and the other factor is a group on which there is a pseudocharacter. For such products we obtain a similar result about the conditions of existence of nontrivial pseudocharacters invariant with respect to certain endomorphisms.     

On existence of invariant measures

Let G be a Lie group, H ≤ G a closed subgroup and M ≈ G/H. In [14] André Weil gave a necessary and sufficient condition for the existence of invariant measures on homogeneous spaces of arbitrary locally compact groups. For Lie groups using the structure theory we give a neater necessary and sufficient condition for the existence of a G-invariant measure on M, cf. Theorems (2.1) and (3.2) in the introduction.     

On maximal transitive sets of generic diffeomorphisms

Abstract. – We construct locally generic C¹-diffeomorphisms of 3-manifolds with maximal transitive Cantor sets without periodic points. The locally generic diffeomorphisms constructed also exhibit strongly pathological features generalizing the Newhouse phenomenon (coexistence of infinitely many sinks or sources). Two of these features are: coexistence of infinitely many nontrivial (hyperbolic and nonhyperbolic) attractors and repellors, and coexistence of infinitely many nontrivial (nonhyperbolic) homoclinic classes.?We prove that these phenomena are associated to the existence of a homoclinic class H(P,f) with two specific properties:?– in a C¹-robust way, the homoclinic class H(P,f) does not admit any dominated splitting,?– there is a periodic point P^′ homoclinically related to P such that the Jacobians of P^′ and P are greater than and less than one, respectively. Manuscrit reĉu le 13 décembre 2000. RID="*" ID="*"This paper was partially supported by CNPq, Faperj, and Pronex Dynamical Systems (Brazil), PICS-CNRS and the Agreement Brazil-France in Mathematics. The authors acknowledge to IMPA and Laboratoire de Topologie, Université de Bourgogne, for the warm hospitality during their visits while preparing this paper. We also acknowledge M.-C. Arnaud, F. Béguin and the referees for their comments on the first version of this paper.     

Stone-weierstrass theorems for group-valued functions

Constructive groups were introduced by Sternfeld in [6] as a class of metrizable groupsG for which a suitable version of the Stone-Weierstrass theorem on the group ofG-valued functionsC(X, G) remains valid. As a way of exploring the existence of such Stone-Weierstrass-type theorems in this context we address the question raised in [6] as to which groups are constructive and prove that a locally compact group with more than two elements is constructive if and only if it is either totally disconnected or homeomorphic to some vector group ℝ ⁿ . It may therefore be concluded that the Stone-Weierstrass theorem can be extended to some noncommutative Lie groups — exactly to those not containing any nontrivial compact subgroup. Research partially supported by Grant CTIDIB/2002/192 of theAgencia Valenciana de Ciencia y Tecnología, and Fundació Caixa-Castelló, grant P1 B2001-08.     

The universal torsion-free image of a group

We show that the universal torsion free homomorphic image of any group given by a sufficiently ‘small’ presentation is locally indicable, and give an application to a conjecture of Levin about equations over torsion free groups. Supported by SERC Visiting Fellowship GR/F 97355.     

Power automorphisms of finitep-groups

For a finite groupG letA(G) denote the group of power automorphisms, i.e. automorphisms normalizing every subgroup ofG. IfG is ap-group of class at mostp, the structure ofA (G) is shown to be rather restricted, generalizing a result of Cooper ([2]). The existence of nontrivial power automorphisms, however, seems to impose restrictions on thep-groupG itself. It is proved that the nilpotence class of a metabelianp-group of exponentp ² possessing a nontrival power automorphism is bounded by a function ofp. The “nicer” the automorphism—the lower the bound for the class. Therefore a “type” for power automorphisms is introduced. Several examples ofp-groups having large power automorphism groups are given.     

On the existence of solutions for nonlinear impulsive periodic viable problems

In this paper we prove the existence of periodic solutions for nonlinear impulsive viable problems monitored by differential inclusions of the type x′(t)∈F(t,x(t))+G(t,x(t)). Our existence theorems extend, in a broad sense, some propositions proved in [10] and improve a result due to Hristova-Bainov in [13].     

Left Ordered Amenable and Locally Indicable Groups

There has been interest recently concerning when a left orderedgroup is locally indicable. Chiswell and Kropholler proved thatevery left ordered solvable-by-finite group is locally indicable,while Bergman gave examples of left ordered groups which arenot locally indicable. This paper proves that every left orderedelementary amenable group is locally indicable. Every solvable-by-finitegroup is elementary amenable, and every elementary amenablegroup is amenable. The author leaves it as an open problem asto whether every left ordered amenable group is locally indicable.     

Differential substitutions of the miura transformation type

The existence of a nontrivial integral and a sufficiently large set of symmetries with respect to one of the characteristics of a hyperbolic equation implies the existence of nontrivial integrals and symmetries with respect to the other characteristic. We classify differential substitutions of the form ω=P(x, u, u _x ) relating families of evolution equations that depend on an arbitrary function. Among such substitutions, there are infinitely many pairwise-nonequivalent ones. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 116, No. 3, pp. 336–348, September, 1998.     

Multiple Nontrivial Solutions for a Class of p-Laplacian Equations

In this paper a class of p-Laplacian equations are considered. The existence of five nontrivial solutions is stated. By the standard supersolution and subsolution method, we prove the existence of minimal positive solution and maximal negative solution in L ^∞(Ω). Furthermore, in virtue of the well-known Mountain-Pass Theorem and Second Deformation Theorem, we can give additional three nontrivial solutions, i.e., one positive solution, one negative solution and one sign-changing solution.     

Periodic groups saturated by finite simple groups <Emphasis Type="Italic">U</Emphasis><Subscript>3</Subscript>(2<Superscript>m</Superscript>)

Let {ie166-01} be a set of finite groups. A group G is said to be saturated by the groups in {ie166-02} if every finite subgroup of G is contained in a subgroup isomorphic to a member of {ie166-03}. It is proved that a periodic group G saturated by groups in a set {U₃(2^m) | m = 1, 2, …} is isomorphic to U₃(Q) for some locally finite field Q of characteristic 2; in particular, G is locally finite. __________ Translated from Algebra i Logika, Vol. 47, No. 3, pp. 288–306, May–June, 2008.     

Symplectic structures on locally compact abelian groups and polarizations

LetX be a locally compact abelian group and ω(.,.) a symplectic structure on it. A polarization for (X, ω) is a pair of totally isotropic closed subgroupsG, G* ofX such thatX =G.G* and ω(.,.) defines a dual pairing ofG andG*. In this paper we describe a class of such groups which always admit a polarization and also discuss their structure. Dedicated to the memory of Professor K G Ramanathan     

Stochastic processes on geometric loop groups,diffeomorphism groups of connected manifolds,and associated unitary representations

This paper is devoted to the investigation of semidirect products of loop groups and homeomorphism or diffeomorphism groups of finite-and infinite-dimensional real, complex, and quaternion manifolds. Necessary statements about quaternion manifolds with quaternion holomorphic transition mappings between charts of atlases are proved. It is shown that these groups exist and have the structure of infinite-dimensional Lie groups, i.e., they are continuous or differentiable manifolds and the composition (f, g) ↦ f ⁻¹ g is continuous or differentiable depending on the smoothness class of groups. Moreover, it is proved that in the cases of complex and quaternion manifolds, these groups have the structures of complex and quaternion manifolds, respectively. Nevertheless, it is proved that these groups do not necessarily satisfy the Campbell-Hausdorff formula even locally outside of the exceptional case of a group of holomorphic diffeomorphisms of a compact complex manifold. Unitary representations of these groups G′, including irreducible ones, are constructed by using quasi-invariant measures on groups G relative to dense subgroups G′. It is proved that this procedure provides a family of cardinality card(ℝ) of pairwise nonequivalent, irreducible, unitary representations. The differentiabilty of such representations is studied. __________ Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 28, Algebra and Analysis, 2005.     

Cayley digraphs and lexicographic product

In this paper, we prove that a Cayley digraph Γ = Cay(G, S) is a nontrivial lexicographical product if and only if there is a nontrivial subgroup H of G such that S∖H is a union of some double cosets of H in G.      

Criteria of prime links in terms of pseudo-characters

Pseudo-characters of groups have recently found applications in the theory of classical knots and links in ℝ³. More precisely, there is a connection between pseudo-characters of Artin’s braid groups and properties of links represented by braids. In the present work, this connection is investigated and the notion of kernel pseudo-characters of braid groups is introduced. It is proved that a kernel pseudo-character ϕ and a braid β satisfy Ιϕ(β)І > C _ϕ, where C _ϕ is the defect of ϕ, then β represents a prime link (i.e., a link that is noncomposite, nonsplit, and nontrivial). Furthermore, the space of braid group pseudo-characters is studied and a way to obtain nontrivial kernel pseudo-characters from an arbitrary braid group pseudo-character that is not a homomorphisrn is described. This allows one to use an arbitrary nontrivial braid group pseudo-character for recognition of prime knots and links. Bibliography: 17 titles.     

On universal locally finite groups

We deal with the question of existence of a universal object in the category of universal locally finite groups; the answer is negative for many uncountable cardinalities; for example, for 2^ℵ ₀, and assuming G.C.H. for every cardinal whose confinality is >ℵ₀. However, if λ>κ when κ is strongly compact and of λ=ℵ₀, then there exists a universal locally finite group of cardinality λ. The idea is to use the failure of the amalgamation property in a strong sense. We shall also prove the failure of the amalgamation property for universal locally finite groups by transferring the kind of failure of the amalgamation property from LF into ULF. We would like to thank Simon Thomas for reading carefully a preliminary version of this paper, proving Lemma 20 and making valuable remarks. Also we thank the United States—Israel Binational Science Foundation for partially supporting this work.     

Multiple solutions for a Robin‐type differential inclusion problem involving the p(x)‐Laplacian

In this paper, we obtain the existence of at least two nontrivial solutions for a Robin‐type differential inclusion problem involving p(x)‐Laplacian type operator and nonsmooth potentials. Our approach is variational, and it is based on the nonsmooth critical point theory for locally Lipschitz functions. Copyright © 2013 John Wiley & Sons, Ltd.     

Systolic inequalities and Massey products in simply-connected manifolds

We show that the existence of a nontrivial Massey product in the cohomology ring H* (X) imposes global constraints upon the Riemannian geometry of a manifold X. Namely, we exhibit a suitable systolic inequality, associated to such a product. This generalizes an inequality proved in collaboration with Y. Rudyak, in the case when X has unit Betti numbers, and realizes the next step in M. Gromov’s program for obtaining geometric inequalities associated with nontrivial Massey products. The inequality is a volume lower bound, and depends on the metric via a suitable isoperimetric quotient. The proof relies upon W. Banaszczyk’s upper bound for the successive minima of a pair of dual lattices. Such an upper bound is applied to the integral lattices in homology and cohomology of X. The possibility of applying such upper bounds to obtain volume lower bounds was first exploited in joint work with V. Bangert. The latter work deduced systolic inequalities from nontrivial cup-product relations, whose role here is played by Massey products. Supported by the Israel Science Foundation (grants no. 620/00, 84/03, and 1294/06)     

Majorants of functions with vanishing integrals over balls

We prove the existence of nontrivial functions in ℝⁿ, n ≥ 2, with vanishing integrals over balls of fixed radius and given majorant of growth. Translated from Ukrains'kyi Matematychnyi Zhurnal, Vol. 60, No. 6, pp. 857–861, June, 2008.     

On local solutions of degenerate differential inclusions

We study the existence and properties of local solution sets for differential inclusions of the form (Ax)′ ∈ F(t, x), where A is a closed linear surjective operator with nontrivial null space and F is a compact set-valued mapping.