The norm problem is considered for elementary operators of the form $U_{a,b}\,{:}\,{\cal A}\,{\longrightarrow}\,{\cal A},\;x\longmapsto axb\,{+}\,bxa (a,\,b\,{\in}\,{\cal A})$ in the special case when ${\cal A}$ is a subalgebra of the algebra of bounded operators on a Banach space. In particular, the lower estimate $\|U_{a,b}\|\geq\|a\|\|b\|$ is established when the Banach space is a Hilbert space and ${\cal A}$ is the algebra of all bounded linear operators.

The main objective of this paper is to establish a large deviation principle for heat kernel measures on loop spaces. It gives an extension of Fang and Zhang's results on loop groups. For the proof, we use the continuity theorem of Lyons' rough path theory.

The paper considers three questions about independent random points uniformly distributed in isotropic symmetric convex bodies $K, T_1,\ldots, T_s$. (a) Let $\varepsilon\,{\in}\, (0,1)$ and let $x_1,\ldots, x_N$ be chosen from K. Is it true that if $N\,{\geq}\, C(\varepsilon )n\log n$, then \[\left\| I-\frac{1}{NL_K^2}\sum_{i=1}^Nx_i\otimes x_i\right\|<\varepsilon\] with probability greater than $1\,{-}\,\varepsilon $? (b) Let $x_i$ be chosen from $T_i$. Is it true that the unconditional norm \[\|{\bf t}\|=\int_{T_1}\!{\ldots}\int_{T_s}\left\|\sum_{i=1}^st_ix_i\right\|_K\,dx_s\ldots dx_1\] is well comparable to the Euclidean norm in ${\mathbb R}^s$? (c) Let $x_1,\ldots, x_N$ be chosen from K. Let ${\mathbb E}\,(K,N):={\mathbb E}\,|{\rm conv}\{ x_1,\ldots, x_N\}|^{1/n}$ be the expected volume radius of their convex hull. Is it true that ${\mathbb E}\,(K,N)\,{\simeq}\, {\mathbb E}\,(B(n),N)$ for all N, where $B(n)$ is the Euclidean ball of volume 1?

It is proved that the answers to these questions are affirmative if there is a restriction to the class of unconditional convex bodies. The main tools come from recent work of Bobkov and Nazarov. Some observations about the general case are also included.

In 1998, Zalesskii proposed to classify all instances of irreducible characters of quasi- simple groups which are of prime power degree. In joint work, Malle and Zalesskii then dealt with all quasi-simple groups with the exception of the alternating groups and their double covers [5]. In an earlier article [1] we have classified all the irreducible characters of $S_n$ of prime power degree and have deduced from this also the corresponding classification for the alternating groups. In the present article we complete Zalesskii's programme by dealing with the final case left open in [5], the double covers of the alternating groups. We derive this result from a corresponding result on the double covers of the symmetric groups. If one is only interested in spin characters, one easily sees that only 2-powers can occur as prime power degrees. However from a combinatorial point of view it is natural to ask more generally: when is the number of shifted standard tableaux of a given shape a prime power? Since our method is independent of the prime, we will answer this question, showing that apart from a few accidental cases for small $n$ only the ‘obvious’ partitions satisfy the prime power condition. Thus in turn for the spin characters, apart from exceptions for small $n$ , the ‘obvious’ spin characters of 2-power degree are indeed the only ones (this confirms the conjecture stated in [5]).

For the $p$-Laplacian $\Delta_p v \,{=}\, {\rm div}\:(|\nabla v|^{p-2}\nabla v)$, $p\,{>}\,1$, the eigenvalue problem $-\Delta_p v + q(|x|)|v|^{p-2}v \,{=}\, \lambda |v|^{p-2}v$ in $\R^n$ is considered under the assumption of radial symmetry. For a first class of potentials $q(r)\,{\to}\,\infty$ as $r\,{\to}\,\infty$ at a sufficiently fast rate, the existence of a sequence of eigenvalues $\lambda_k\,{\to}\,\infty$ if $k\,{\to}\,\infty$ is shown with eigenfunctions belonging to $L^p(\R^n)$. In the case $p\,{=}\,2$, this corresponds to Weyl's limit point theory. For a second class of power-like potentials $q(r)\,{\to}\,{-}\infty$ as $r\,{\to}\,\infty$ at a sufficiently fast rate, it is shown that, under an additional boundary condition at $r\,{=}\,\infty$, which generalizes the Lagrange bracket, there exists a doubly infinite sequence of eigenvalues $\lambda_k$ with $\lambda_k \,{\to}\,\pm \infty$ if $k\,{\to}\,\pm\infty$. In this case, every solution of the initial value problem belongs to $L^p(\R^n)$. For $p\,{=}\,2$, this situation corresponds to Weyl's limit circle theory.

A theorem of Hall extends the sylow theory to π-subgroups of a finite solvable group for any set of primes π. This theorem has been generalized to solvable periodic linear groups [21] and to other similar settings [19]. We consider the same problem in a model-theoretic context.

In model theory, the study of ω-stable groups generalizes the classical theory of algebraic groups in the case of a algebraically closed base field, and is closely connected with certain aspects of the general structure theory developed by Shelah, particularly in connection with the more geometric theory of Zilber, Buechler, Hrushovski, Pillay, and others. In this connection, the primary concern is with the structure of simple ω-stable groups of finite rank. One way to approach the study of ω-stable groups is by generalizing some of the methods of finite group theory to this setting. One anticipates that character theory and counting arguments will not be available, though one would hope to recover much of the ‘local analysis’. Unfortunately there is as yet no very satisfactory sylow theory for ω-stable groups, except for the prime 2 [4]. One of us (Nesin) noticed initially that there is a sylow theorem for connected solvable ω-stable groups of finite Morley rank; this prompted us to look for a generalization along the following lines.

Let $f(z)$ be a transcendental meromorphic function. The paper investigates, using the hyperbolic metric, the relation between the forward orbit $P(f)$ of singularities of $f^{-1}$ and limit functions of iterations of $f$ in its Fatou components. It is mainly proved, among other things, that for a wandering domain $U$ , all the limit functions of $\{f^n\vert_U\}$ lie in the derived set of $P(f)$ and that if $f^{np}\vert_V\rightarrow q(n\rightarrow +\infty)$ for a Fatou component $V$ , then either $q$ is in the derived set of $S_p(f)$ or $f^p(q) = q$ . As applications of main theorems, some sufficient conditions of the non-existence of wandering domains and Baker domains are given.

Explicit bounds are given for the residues at $s\,{=}\,1$ of the Dedekind zeta functions of number fields. As a consequence, a simple proof of the Brauer-Siegel theorem and explicit lower bounds for class numbers of number fields are obtained. Compared with Stark's original approach, the paper is explicit and more satisfactory for number fields containing quadratic subfields. Examples are given of fully explicit lower bounds for class numbers of various types of number fields, for example normal and non-normal number fields of odd degree, with an emphasis on cubic fields, real cyclic quartic number fields, and non-normal quartic number fields containing an imaginary quadratic subfield.

For bounded Hilbert space operators X, An and Bn, n = 1, 2, …,

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for all 1 [les ] p < ∞ and

formula here

These inequalities involve some estimates for the norm of elementary operators with the range contained in the Schatten p-ideals.

Localization and dévissage theorems are proved for the hermitian $K$-theory of rings that are analogous to well-known theorems in algebraic $K$-theory. The proofs rely on, among other things, a study of derived categories, a generalization of a theorem of Pedersen and Weibel to the hermitian setting, and a cofinality result for triangular Witt groups. Applications include a proof of a conjecture of Karoubi and algebraic Bott periodicity.

Given the Diophantine equation a2+b2+c2=3abc, a solution triple of natural numbers (a, b, c) can be arranged in ascending order so that a[les ]b[les ]c. Then, given the largest element c, one can ask whether this uniquely determines the triple. This is referred to as the Markoff conjecture. The paper proves that, if c is prime, then there is indeed only one triple that solves the equation with c as the largest element. The proof uses only standard algebraic number theory, but it was prompted by geometric considerations.

For any given real number $\alpha$ with bounded partial quotients, we construct explicitly continuum many real numbers $\beta$ with bounded partial quotients for which the pair $(\alpha, \beta)$ satisfies a strong form of the Littlewood conjecture. Our proof is elementary and rests on the basic theory of continued fractions.

The Cauchy problem is studied for the nonlinear equations with fractional power of the negative Laplacian \[ \left\{ \begin{array}{@{}r@{\,}c@{\,}l@{\qquad}l} u_{t}+( -\Delta ) ^{{\alpha}/{2}}u+u^{1+\sigma } &=&0, & x\in {\mathbf{R}}^{n},\text{ }t>0, \\[4pt] u( 0,x) &=& u_{0} ( x), &x\in {\mathbf{R}}^{n}, \end{array} \right. \label{A} \] where $\alpha \in ( 0,2)$, with critical $\sigma ={\alpha }/{ n}$ and sub-critical $\sigma \in ( 0,{\alpha }/{n}) $ powers of the nonlinearity. Let $u_{0}\,{\in}\, \mathbf{L}^{1,a}\cap \mathbf{L}^{\infty }\cap \mathbf{C}, $$u_{0}( x) \,{\geq}\, 0$ in $\mathbf{R}^{n},$$\theta \,{=}\,\int_{ \mathbf{R}^{n}}u_{0}( x) \,dx\,{>}\,0.$ The case of not small initial data is of interest. It is proved that the Cauchy problem has a unique global solution $u \in \mathbf{C}( [0,\infty); \mathbf{L}^{\infty }\cap \mathbf{L}^{1,a}\cap \mathbf{C})$ and the large time asymptotics are obtained.

The moduli theory of Calabi–Yau threefolds is investigated, and using Griffiths' work on the period map, some finiteness results are derived. In particular, a prediction of Morrison's cone conjecture is confirmed.

For a sequence (cn) of complex numbers, the quadratic polynomials fcn(z) := z2 + cn and the sequence (Fn) of iterates Fn := fcn∘…∘fc1 are considered. The Fatou set [Fscr ](cn) is by definition the set of all z ∈ [Copf ]ˆ such that (Fn) is normal in some neighbourhood of z, while the complement of [Fscr ](cn) is called the Julia set [Jscr ](cn). The aim of this article is to study the connectedness and stability of the Julia set [Jscr ](cn) provided that the sequence (cn) is bounded.

We introduce two related families of polynomials, easily computable by simple recursions into which any Kazhdan–Lusztig (and inverse Kazhdan–Lusztig) polynomial of any Coxeter group can be expanded linearly, and we give combinatorial interpretations to the coefficients in these expansions. This yields a combinatorial rule for computing the Kazhdan–Lusztig polynomials in terms of paths in a directed graph, and a completely combinatorial reformulation of the nonnegativity conjecture [15, p. 166].

We present the classification of all real hypersurfaces in complex hyperbolic space $\mathbb{C}H^{n}$, $n \geq 3$, with three distinct constant principal curvatures.

A point λ in the complex plane is said to be free if the group generated by the matrices

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is free. The paper gives an infinite family of polynomials whose roots are the non-free points. The main idea in the paper is to employ a symmetry relation.

In this paper we study quaternion-Kähler manifolds endowed with an isometric S1-action. We consider the corresponding moment map μ and prove that the only compact quaternion-Kähler manifold with positive scalar curvature which admits an isometric circle action free on μ−1(0) is the quaternionic projective space ℍPn.

Necessary and sufficient conditions are given for linearly recurrent Cantor dynamical systems to have measurable and continuous eigenfunctions. Also an example of a linearly recurrent system with a nontrivial Kronecker factor and a trivial maximal equicontinuous factor is constructed explicitly.