Without using representations of quasitriangular ribbon Hopf algebras, Hennings, Kauffman and Radford, Ohtsuki and the author gave different methods to construct invariants of links and 3-manifolds respectively. To understand these different methods and the resultant invariants, we made a comprehensive comparison study in this paper. We show the relations among the universal invariants of framed links defined by these different authors. We also figured out the relations among the resultant invariants of 3-manifolds defined by these different authors. Ignoring the difference by scalar constants and the inversion of Hopf algebras, we found that the invariants of 3-manifolds obtained by these authors are the same or equivalent to each other. Therefore, in a sense, there is only one way to construct invariants of 3-manifolds without using representation theory of Hopf algebras.

We establish some properties of Thurston's asymmetric metric L on the Teichmüller space of a surface of genus with punctures and with negative Euler characteristic. We study convergence of sequences of elements in in the sense of L, as well as sequences that tend to infinity in . We show that the topology that the asymmetric metric L induces on Teichmüller space is the same as the usual topology. Furthermore, we show that L satisfies the axioms of a (not necessarily symmetric) metric in the sense of Busemann and conclude that L is complete in the sense of Busemann.

We present an example of a Banach space whose numerical index is strictly greater than the numerical index of its dual, giving a negative answer to a question which has been latent since the beginning of the seventies. We also show a particular case in which the numerical index of the space and the one of its dual coincide.

The famous Haken–Kneser–Milnor theorem states that every 3-manifold can be expressed in a unique way as a connected sum of prime 3-manifolds. The analogous statement for 3-orbifolds has been part of the folklore for several years, and it was commonly believed that slight variations on the argument used for manifolds would be sufficient to establish it. We demonstrate in this paper that this is not the case, proving that the apparently natural notion of “essential” system of spherical 2-orbifolds is not adequate in this context. We also show that the statement itself of the theorem must be given in a substantially different way. We then prove the theorem in full detail, using a certain notion of “efficient splitting system.”

We determine the set of Busemann points of an arbitrary finite-dimensional normed space. These are the points of the horofunction boundary that are the limits of “almost-geodesics”. We prove that all points in the horofunction boundary are Busemann points if and only if the set of extreme sets of the dual unit ball is closed in the Painlevé–Kuratowski topology.

Let e denote the Euler class on the space of representations of the fundamental group Γg of the closed surface Σg of genus g. Goldman showed that the connected components of are precisely the inverse images e−1(k), for 2−2g≤ k≤ 2g−2, and that the components of Euler class 2−2g and 2g−2 consist of the injective representations whose image is a discrete subgroup of . We prove that non-faithful representations are dense in all the other components. We show that the image of a discrete representation essentially determines its Euler class. Moreover, we show that for every genus and possible corresponding Euler class, there exist discrete representations.

For r ∈ [0, 1] let μr be the Bernoulli measure on the Cantor set given as the infinite power of the measure on {0, 1} with weights r and 1 − r. For r, s ∈ [0, 1] it is known that the measure μr is continuously reducible to μs (that is, there is a continuous map sending μr to μs) if and only if s can be written as a certain kind of polynomial in r; in this case s is said to be binomially reducible to r. In this paper we answer in the negative the following question posed by Mauldin:

Is it true that the product measures μrand μsare homeomorphic if and only if each is a continuous image of the other, or, equivalently, each of the numbersrandsis binomially reducible to the other?

We consider the class Sp of functions univalent in the unit disk Δ.

In [1] it was shown that if f∈Sp and p is large, (0.1) Here we show that there exists f in Sp for p=1,2,. . . such that where C0 is a positive absolute constant.

We introduce and study two new notions of amenability for Banach algebras. In particular we compare these notions with some of those studied earlier. We show that several classes of Banach algebras, including certain Banach algebras related to locally compact groups, are responsive to these notions.

A spray is a second-order differential equation field on the slit tangent bundleof a differentiable manifold, which is homogeneous of degree 1 in the fibrecoordinates in an appropriate sense; two sprays which are projectivelyequivalent have the same base-integral curves up to reparametrization. We showhow, when the base manifold is two-dimensional, to construct from any projectiveequivalence class of sprays a conformal class of metrics on a four-dimensionalmanifold, of signature (2, 2); the Weyl conformal curvature of these metrics issimply related to the projective curvature of the sprays, and the geodesics ofthe sprays determine null geodesics of the metrics. The metrics in question havepreviously been obtained by Nurowski and Sparling (Classical and Quantum Gravity20 (2003) 4995–5016), by a differentmethod involving the exploitation of a close analogy between the Cartan geometryof second-order ordinary differential equations and of three-dimensionalCauchy–Riemann structures. From this perspective the derived metricsare seen to be analoguous to those defined by Fefferman in the CR theory, andare therefore said to be of Fefferman type. Our version of the constructionreveals that the Fefferman-type metrics are derivable from the scalar tripleproduct, both directly in the flat case (which we discuss in some detail) and bya simple extension in general. There is accordingly in our formulation a verysimple expression for a representative metric of the class in suitablecoordinates.

We give estimates of the essential norms of weighted composition operators acting between Bergman spaces on strongly pseudoconvex domains. We also characterize boundedness and compactness of these operators.

A formula for the generalized Schwarz–Christoffel conformal mapping from a bounded multiply connected circular domain to an unbounded multiply connected polygonal domain is derived. The formula for the derivative of the mapping function is shown to contain a product of powers of Schottky–Klein prime functions associated with the circular preimage domain. Two analytical checks of the new formula are given. First, it is compared with a known formula in the doubly connected case. Second, a new slit mapping formula from a circular domain to the triply connected region exterior to three slits on the real axis is derived using separate arguments. The derivative of this independently-derived slit mapping formula is shown to correspond to a degenerate case of the new Schwarz–Christoffel mapping. The example of the mapping to the triply connected region exterior to three rectangles centred on the real axis is considered in detail.

We investigate the structure of 3-dimensional complete minimal hypersurfaces in the unit sphere with Gauss–Kronecker curvature identically zero.

The only stable singularities of a real map-germ are isolated transverse double-points. All -simple germs f have a deformation with the maximal number d(f) of real double-points (this is a partial generalization to higher n of the result of A'Campo [1] and Gusein-Zade [13] that all plane curve-germs have a deformation with δ real double points, with the extra hypothesis of -simplicity). The proof of this result is based on a classification of all -simple orbits.

A recent characterisation of Fock-adapted contraction operator stochastic cocycles on a Hilbert space, in terms of their associated semigroups, yields a general principle for the construction of such cocycles by approximation of their stochastic generators. This leads to new existence results for quantum stochastic differential equations. We also give necessary and sufficient conditions for a cocycle to satisfy such an equation.

Let f be a function transcendental and meromorphic in the plane, and define g(z) by g(z) = Δf(z) = f(z + 1) − f(z). A number of results are proved concerning the existence of zeros of g(z) or g(z)/f(z), in terms of the growth and the poles of f. The results may be viewed as discrete analogues of existing theorems on the zeros of f' and f'/f.

In analogy to the classical isomorphism between and , we show that a large class of moderate linear mappings acting between the space of Colombeau rapidly decreasing generalized functions and the space of temperate ones admits generalized integral representations, with kernels belonging to . Furthermore, this result contains the classical one.

One usually assumes that the Schrödinger operator on a thin quantum network (“fattened graph”) can be simulated by the ordinary Schrödinger operator on the corresponding one-dimensional quantum graph. On the other hand, each quantum graph can be constructed of standard elements – star graphs. We prove that a thin star-shaped quantum network which consists of a compact domain and a few straight semi-infinite quantum wires, with a two-dimensional Schrödinger operator on it, can be simulated by the corresponding solvable model in form of a one-dimensional star graph: an outer space, with an ordinary Schrödinger operator on the leads, a resonance vertex supplied with an inner space and a finite matrix in it and an appropriate boundary condition connecting the inner and outer components of elements from the domain of the model. The model is (locally) quantitatively consistent: the scattering matrix of the model on a certain spectral interval serves an approximation of the scattering matrix of the network. The role of the constructed star-graph model as a “jump-start” in analytic perturbation procedure on continuous spectrum is discussed.

PM(E) denotes the set of pseudomeasures on with support in the closed set E ⊆ . Then y ∈ is not in E if and only if there is a neighbourhood W of y with uniformly for w ∈ W and S ∈ PM(E) with ‖S‖PM ≤ 1. This improves previous results by adding “uniformly” and its scope. The proof uses the fact that squashing the central spike of the Fejer kernel leads to A-norm convergence.

We establish a combinatorial formula for homogeneous moments and give some examples where it can be put to use. An application to the statistical mechanics of interacting gauged vortices is discussed.