Hyperbolic structure preserving isomorphisms of Markov shifts

In this paper we consider metric isomorphisms of Markov shifts which are also isomorphisms of the hyperbolic structures of the shift spaces. We prove that such isomorphisms need not be finitary, and that finitary isomorphisms need not preserve the hyperbolic structures unless they have finite expected code lengths. In particular we show that certain explicity computable invariants previously associated with finitary isomorphisms with finite expected code lengths are, in fact, invariants of the hyperbolic structure of the Markov shifts.     

Quasiconformal motions and isomorphisms of continuous families of Möbius groups

In their paper [17], Sullivan and Thurston introduced the notion of quasiconformal motions, and proved an extension theorem for quasiconformal motions over an interval. We prove some new properties of (normalized) quasiconformal motions of a closed set E in the Riemann sphere, over connected Hausdorff spaces. As a spin-off, we strengthen the result of Sullivan and Thurston, and show that if a quasiconformal motion of E over an interval has a certain group-equivariance property, then the extended quasiconformal motion can be chosen to have the same group-equivariance property. Our main theorem proves a result on isomorphisms of continuous families of Möbius groups arising from a group-equivariant quasiconformal motion of E over a path-connected Hausdorff space. Our techniques connect the Teichmüller space of the closed set E with quasiconformal motions of E.     

Solvable Permutation Groups and Orbits on Power Sets

We consider the class ? of finitely generated toral relatively hyperbolic groups. We show that groups from ? are commutative transitive and generalize a theorem proved by Benjamin Baumslag in [3 Baumslag, B. (1967). Residually free groups. Prceedings of the London Mathematical Society 17(3):402–418.[Crossref] , [Google Scholar]] to this class. We also discuss two definitions of (fully) residually-𝒞 groups, i.e., the classical Definition 1.1 and a modified Definition 1.4. Building upon results obtained by Ol'shanskii [18 Ol'shanskii, A. Yu. (1993). On residualing homomorphisms and G-subgroups of hyperbolic groups. International Journal of Algebra Computation 3:365–409.[Crossref] , [Google Scholar]] and Osin [22 Osin, D. V. (2010). Small cancellations over relatively hyperbolic groups and embedding theorems. Annals of mathematics 172:1–39.[Crossref], [Web of Science ®] , [Google Scholar]], we prove the equivalence of the two definitions for 𝒞 = ?. This is a generalization of the similar result obtained by Ol'shanskii for 𝒞 being the class of torsion-free hyperbolic groups. Let Γ ∈ ? be non-abelian and non-elementary. Kharlampovich and Miasnikov proved in [14 Kharlampovich, O., Myasnikov, A. (2012). Limits of relatively hyperbolic groups and Lyndon's completions. Journal of the European Math. Soc. 14:659–680.[Crossref], [Web of Science ®] , [Google Scholar]] that a finitely generated fully residually-Γ group G embeds into an iterated extension of centralizers of Γ. We deduce from their theorem that every finitely generated fully residually-Γ group embeds into a group from ?. On the other hand, we give an example of a finitely generated torsion-free fully residually-? group that does not embed into a group from ?; ? is the class of hyperbolic groups.     

Existence ofBV absolute discontinuous minima for modified multiple integrals of the calculus of variations

We continue here the discussion on the existence of discontinuousBV minima, for a class of multiple integrals of the calculus of variationsI, we have started in [2] in view of possible studies on hyperbolic partial differential equations. Besides the associated Serrin integralJ, based onL ₁-convergence, we take into consideration a modified Serrin-type functionalJ ^*. This new integralJ ^* will be needed in [3] to prove Rankine-Hugoniot type properties.     

Hyperbolicity of generic deformations

We modify the deformation method in [16] to construct further examples of Kobayashi hyperbolic surfaces in \(\mathbb{P}_\mathbb{C}^3 \) of any even degree d ? 8.     

Congruences between word length statistics for the finitary alternating and symmetric groups

Bacher and de la Harpe (arxiv:1603.07943, 2016) study conjugacy growth series of infinite permutation groups and their relationships with p(n), the partition function, and \(p(n)_\mathbf{e }\), a generalized partition function. They prove identities for the conjugacy growth series of the finitary symmetric group and the finitary alternating group. The group theory due to Bacher and de la Harpe (arxiv:1603.07943, 2016) also motivates an investigation into congruence relationships between the finitary symmetric group and the finitary alternating group. Using the Ramanujan congruences for the partition function p(n) and Atkin’s generalization to the k-colored partition function \(p_{k}(n)\), we prove the existence of congruence relations between these two series modulo arbitrary powers of 5 and 7, which we systematically describe. Furthermore, we prove that such relationships exist modulo powers of all primes \(\ell \ge 5\).     

On the Best Exponent in Markov Inequality

Let E be a compact set preserving the Markov inequality and m(E) be its best exponent i.e., m(E) is the infimum of all possible exponents in this inequality on E. It is known that $\alpha (E) \le \frac1{m(E)}$ where α(E) is the best exponent in Hölder continuity property of the (pluri)complex Green function (with pole at infinity) of E. We show that if E???? ^N (or ? ^N ) with N?≥?2 then the Markov inequality need not be fulfilled with m(E). We also construct a set E????² such that the Markov inequality holds at the tip of exponential cusps composing E but for the whole set E we have m(E)?=?∞. Moreover, we prove that sup m(E)?=?∞ where the supremum is taken over all compact sets E???? preserving the Markov inequality. Finally, we prove that if E is a Markov set in ? then its image F(E) under a holomorphic mapping F is a Markov set too. More precisely, we prove that $m(F(E))\leq m(E)\cdot \Big(1+ \max\limits_{ \partial E\cap\{F'(t)=0\}}\textrm{ord}_t F'\Big)$ .     

Local derivations of finitary incidence algebras

Let P be a partially ordered set, R a commutative ring with identity and FI(P,R) the finitary incidence algebra of P over R. We prove that each R-linear local derivation of FI(P,R) is a derivation, which partially generalizes Theorem 3 of [21].     

Endomorphisms of a Lebesgue space III

A new invariant is introduced for regular isomorphisms, which are isomorphisms by codes that anticipate a finite amount of the future. With the help of this invariant it is shown that the Bernoulli automorphism (p, q) is not regularly isomorphic to the Markov automorphism ( _pq ^qp ),p ≠q, and that neither of these is regularly isomorphic to the Markov automorphism ( _qp ^pq ).     

Very Hyperbolic Polynomials

A real polynomial in one variable is hyperbolic if it has only real roots. A function f is a primitive of order k of a function g if f ^(k) = g. A hyperbolic polynomial is very hyperbolic if it has hyperbolic primitives of all orders. In the paper, we prove a property of the domain of very hyperbolic polynomials and describe this domain in the case of degree 4.     

Existence of positive solutions to nonlinear elliptic equations involving critical Sobolev exponents

In this paper we extend the results of Brezis and Nirenberg in [4] to the problem $$\left\{ \begin{gathered} Lu = - D_i (a_{ij} (x)D_j u) = b(x)u^p + f(x,u) in\Omega , \hfill \\ p = (n + 2)/(n - 2) \hfill \\ u > 0 in\Omega , u = 0 \partial \Omega , \hfill \\ \end{gathered} \right.$$ whereL is a uniformly elliptic operator,b(x)≥0,f(x,u) is a lower order perturbation ofu ^p at infinity. The existence of solutions to (A) is strongly dependent on the behaviour ofa _ij (x), b(x) andf(x, u). For example, for any bounded smooth domain Ω, we have \(a_{ij} \left( x \right) \in C\left( {\bar \Omega } \right)\) such thatLu=u ^p possesses a positive solution inH ₀ ¹ (Ω). We also prove the existence of nonradial solutions to the problem ?Δu=f(|x|, u) in Ω,u>0 in Ωu=0 on ?Ω, Ω=B(0,1). for a class off(r, u).     

Small volume closed hyperbolic 4-manifolds

Further examples of non-orientable compact hyperbolic 4-manifoldsof volume 32²/3 arising from torsion-free subgroups of the [5,3, 3, 3] Coxeter group are given. These are the smallest knownclosed hyperbolic 4-manifolds and arise by consideration ofmaps from the [5, 3, 3, 3] Coxeter group onto the simple simplecticgroup S₄(4).     

Computing the determinantal representations of hyperbolic forms

The numerical range of an n × n matrix is determined by an n degree hyperbolic ternary form. Helton-Vinnikov confirmed conversely that an n degree hyperbolic ternary form admits a symmetric determinantal representation. We determine the types of Riemann theta functions appearing in the Helton-Vinnikov formula for the real symmetric determinantal representation of hyperbolic forms for the genus g = 1. We reformulate the Fiedler-Helton-Vinnikov formulae for the genus g = 0, 1, and present an elementary computation of the reformulation. Several examples are provided for computing the real symmetric matrices using the reformulation.     

A Markov copula model with regime switching and its application

Regime switching, which is described by a Markov chain, is introduced in a Markov copula model. We prove that the marginals (X,H ⁱ ), i = 1, 2, 3 of the Markov copula model (X,H) are still Markov processes and have martingale property. In this proposed model, a pricing formula of credit default swap (CDS) with bilateral counterparty risk is derived.     

Right Markov Processes and Systems of Semilinear Equations with Measure Data

In the paper we prove the existence of probabilistic solutions to systems of the form ?Au = F(x, u) + μ, where F satisfies a generalized sign condition and μ is a smooth measure. As for A we assume that it is a generator of a Markov semigroup determined by a right Markov process whose resolvent is order compact on L¹. This class includes local and nonlocal operators corresponding to Dirichlet forms as well as some operators which are not in the variational form. To study the problem we introduce new concept of compactness property relating the underlying Markov process to almost everywhere convergence. We prove some useful properties of the compactness property and provide its characterization in terms of Meyer’s property (L) of Markov processes and in terms of order compactness of the associated resolvent.     

On Isomorphisms Between Integral Table Algebras and Applications to Finite Groups and Association Schemes

A problem that has been open for a long time is whether an automorphism of the center of the integral group ring of a finite group permutes the class sums. As a generalization, the similar problem for integral table algebras has also been studied in a few papers. In this paper we further the investigation of the problem for integral C-algebras and table algebras. We will first present some necessary and sufficient conditions under which an algebra isomorphism between integral C-algebras is monomial, and as an application, obtain a conceptual proof of the class sum correspondence theorem of group rings of finite groups. Then we prove that an algebra isomorphism compatible with degree maps between standard integral nilpotent table algebras over the ring of algebraic integers is exact. As a direct consequence, we get Hertweck's result [6 Hertweck , M. ( 2008 ). On isomorphisms between centers of integral group rings of finite groups . Proc. Amer. Math. Soc. 136 : 1539 – 1547 .[Crossref], [Web of Science ®] , [Google Scholar]] for finite nilpotent groups. An application to association schemes is also presented.