We obtain a new representation for the solution to the operator Sylvester equation in the form of a Stieltjes operator integral. We also formulate new sufficient conditions for the strong solvability of the operator Riccati equation that ensures the existence of reducing graph subspaces for block operator matrices. Next, we extend the concept of the Lifshits-Krein spectral shift function associated with a pair of self-adjoint operators to the case of pairs of admissible operators that are similar to self-adjoint operators. Based on this new concept we express the spectral shift function arising in a perturbation problem for block operator matrices in terms of the angular operators associated with the corresponding perturbed and unperturbed eigenspaces.

In this paper, we construct abelian varieties associated to Gauss’ and Appell–Lauricella hypergeometric series. Abelian varieties of this kind and the algebraic curves we define to construct them were considered by several authors in settings ranging from monodromy groups (Deligne, Mostow), exceptional sets (Cohen, Wolfart, Wüstholz), modular embeddings (Cohen, Wolfart) to CM-type (Cohen, Shiga, Wolfart) and modularity (Darmon). Our contribution is to provide a complete, explicit and self-contained geometric construction.

Let $\mathbb{F}$ be a finite real abelian extension of $\mathbb{Q}$. Let $M$ be an odd positive integer. For every squarefree positive integer $r$ the prime factors of which are congruent to 1 modulo $M$ and split completely in $\mathbb{F}$, the corresponding Kolyvagin class ${{k}_{r}}\in {{\mathbb{F}}^{\times }}/{{\mathbb{F}}^{\times M}}$ satisfies a remarkable and crucial recursion which for each prime number $\ell $ dividing $r$ determines the order of vanishing of ${{k}_{r}}$ at each place of $\mathbb{F}$ above $\ell $ in terms of ${{k}_{r/\ell }}$. In this note we give the recursion a new and universal interpretation with the help of the double complex method introduced by Anderson and further developed by Das and Ouyang. Namely, we show that the recursion satisfied by Kolyvagin classes is the specialization of a universal recursion independent of $\mathbb{F}$ satisfied by universal Kolyvagin classes in the group cohomology of the universal ordinary distribution à la Kubert tensored with $\mathbb{Z}/M\mathbb{Z}$. Further, we show by a method involving a variant of the diagonal shift operation introduced by Das that certain group cohomology classes belonging (up to sign) to a basis previously constructed by Ouyang also satisfy the universal recursion.

We extend to the setting of polynomials over a finite field certain estimates for short Kloosterman sums originally due to Karatsuba. Our estimates are then used to establish some uniformity of distribution results in the ring ${{\mathbb{F}}_{q}}\left[ x \right]\,/\,M\left( x \right)$ for collections of polynomials either of the form ${{f}^{-1}}{{g}^{-1}}$ or of the form ${{f}^{-1}}{{g}^{-1}}\,+\,afg$, where $f$ and $g$ are polynomials coprime to $M$ and of very small degree relative to $M$, and $a$ is an arbitrary polynomial. We also give estimates for short Kloosterman sums where the summation runs over products of two irreducible polynomials of small degree. It is likely that this result can be used to give an improvement of the Brun-Titchmarsh theorem for polynomials over finite fields.

Soit $G$ le groupe des points définis sur un corps $p$-adique d'un groupe réductif connexe. A l'aide des caractères virtuels supertempérés de $G$, on prouve (conjectures de Clozel) que toute représentation irréductible tempérée de $G$ est irréductiblement induite d'une essentielle d'un sousgroupe de Lévi de $G$.

It is well known that rather general mutation-recombination models can be solved algorithmically (though not in closed form) by means of Haldane linearization. The price to be paid is that one has to work with a multiple tensor product of the state space one started from.

Here, we present a relevant subclass of such models, in continuous time, with independent mutation events at the sites, and crossover events between them. It admits a closed solution of the corresponding differential equation on the basis of the original state space, and also closed expressions for the linkage disequilibria, derived by means of Möbius inversion. As an extra benefit, the approach can be extended to a model with selection of additive type across sites. We also derive a necessary and sufficient criterion for the mean fitness to be a Lyapunov function and determine the asymptotic behaviour of the solutions.

Soit $G$ un groupe fini agissant sur une courbe algébrique projective et lisse $X$ sur un corps algébriquement clos $k$. Dans cet article, on donne une formule de Riemann-Roch pour la caractéristique d'Euler équivariante d'un $G$-faisceau inversible $\mathcal{L}$, à valeurs dans l'anneau ${{R}_{k}}\left( G \right)$ des caractères du groupe $G$. La formule donnée a un bon comportement fonctoriel en ce sens qu'elle relève la formule classique le long du morphisme dim: ${{R}_{k}}\left( G \right)\to \mathbb{Z}$, et est valable même pour une action sauvage. En guise d'application, on montre comment calculer explicitement le caractère de l'espace des sections globales d'une large classe de $G$-faisceaux inversibles, en s'attardant sur le cas particulier délicat du faisceau des différentielles sur la courbe.

In this paper we estimate the $\left( {{L}^{p}}-{{L}^{2}} \right)$-norm of the complex harmonic projectors $\pi \ell {\ell }',\,1\le p\le 2$, uniformly with respect to the indexes $\ell,{\ell}'$. We provide sharp estimates both for the projectors ${{\pi }_{\ell{\ell}'}}$, when $\ell,{\ell}'$ belong to a proper angular sector in $\mathbb{N}\,\times \,\mathbb{N}$, and for the projectors ${{\pi }_{\ell0}}$ and ${{\pi }_{0\ell}}$. The proof is based on an extension of a complex interpolation argument by C. Sogge. In the appendix, we prove in a direct way the uniform boundedness of a particular zonal kernel in the ${{L}^{1}}$ norm on the unit sphere of ${{\mathbb{R}}^{2n}}$.

A theory of renormalization of divergent integrals over torus periods on $\text{GL}\left( 3 \right)$ is given, based on a relative truncation. It is shown that the renormalized periods of Eisenstein series have unexpected functional equations.

We study the singular integral operator

$${{T}_{\Omega ,\alpha }}f\left( x \right)\,=\,\text{p}\text{.v}\text{.}\,{{\int }_{{{R}^{n}}}}\,b\left( \left| y \right| \right)\Omega \left( {{y}'} \right){{\left| y \right|}^{-n-\alpha }}\,f\left( x\,-\,y \right)\,dy,$$

defined on all test functions $f$, where $b$ is a bounded function, $\alpha \ge 0,\,\Omega \left( {{y}'} \right)$ is an integrable function on the unit sphere ${{S}^{n-1}}$ satisfying certain cancellation conditions. We prove that, for $1\,<\,p\,<\infty$, ${{T}_{\Omega ,\alpha }}$ extends to a bounded operator from the Sobolev space $L_{\alpha }^{p}$ to the Lebesgue space ${{L}^{p}}$ with $\Omega$ being a distribution in the Hardy space ${{H}^{q}}\left( {{S}^{n-1}} \right)$ where $q=\frac{n-1}{n-1+\alpha }$. The result extends some known results on the singular integral operators. As applications, we obtain the boundedness for ${{T}_{\Omega ,\alpha }}$ on the Hardy spaces, as well as the boundedness for the truncated maximal operator $T_{\Omega ,m}^{*}$.

Let $\mathbb{K}$ be a field of characteristic zero, and $*\,=\,t$ the transpose involution for the matrix algebra ${{M}_{2}}\left( \mathbb{K} \right)$. Let $\mathfrak{U}$ be a proper subvariety of the variety of algebras with involution generated by $\left( {{M}_{2}}\left( \mathbb{K} \right),\,* \right)$. We define two sequences of algebras with involution ${{R}_{p}},\,{{S}_{q}}$, where $p,\,q\,\in \,\mathbb{N}$. Then we show that ${{T}_{*}}\left( \mathfrak{U} \right)$ and ${{T}_{*}}\left( {{R}_{p}}\oplus \,{{S}_{q}} \right)$ are $*$-asymptotically equivalent for suitable $p,\,q$.

This note signals an error in the above paper by giving a counter-example.

The main problem that is solved in this paper has the following simple formulation (which is not used in its solution). The group $K={{O}_{p}}\left( C \right)\times {{O}_{q}}\left( C \right)$ acts on the space ${{M}_{p,\,q}}\,\text{of}\,p\,\times \,q$ complex matrices by $\left( a,b \right)\cdot x=ax{{b}^{-1}}$, and so does its identity component ${{K}^{0}}=\text{S}{{\text{O}}_{p}}\left( \text{C} \right)\times \text{S}{{\text{O}}_{\text{q}}}\left( \text{C} \right)$. A $K$-orbit (or ${{K}^{0}}$-orbit) in ${{M}_{p,q}}$ is said to be nilpotent if its closure contains the zero matrix. The closure, $\bar{\mathcal{O}}$, of a nilpotent $K$-orbit (resp. ${{K}^{0}}$-orbit) $\mathcal{O}$ in ${{M}_{p,q}}$ is a union of $\mathcal{O}$ and some nilpotent $K$-orbits (resp. ${{K}^{0}}$-orbits) of smaller dimensions. The description of the closure of nilpotent $K$-orbits has been known for some time, but not so for the nilpotent ${{K}^{0}}$-orbits. A conjecture describing the closure of nilpotent ${{K}^{0}}$-orbits was proposed in $[11]$ and verified when $\min \left( p,\,q \right)\le 7$. In this paper we prove the conjecture. The proof is based on a study of two prehomogeneous vector spaces attached to $\mathcal{O}$ and determination of the basic relative invariants of these spaces.

The above problem is equivalent to the problem of describing the closure of nilpotent orbits in the real Lie algebra $\mathfrak{s}\mathfrak{o}\left( p,\,q \right)$ under the adjoint action of the identity component of the real orthogonal group $\text{O}\left( p,\,q \right)$.

We describe new construction principles for infinite-dimensional Lie groups. In particular, given any measure space $\left( X,\,\sum ,\,\mu \right)$ and (possibly infinite-dimensional) Lie group $G$, we construct a Lie group ${{L}^{\infty }}\left( X,G \right)$, which is a Fréchet-Lie group if $G$ is so. We also show that the weak direct product $\prod{_{i\in I}^{*}{{G}_{i}}}$ of an arbitrary family ${{\left( {{G}_{i}} \right)}_{i\in I}}$ of Lie groups can be made a Lie group, modelled on the locally convex direct sum ${{\oplus }_{i\in I}}L\left( {{G}_{i}} \right)$ .

A topology on $\mathbb{Z}$, which gives a nice proof that the set of prime integers is infinite, is characterised and examined. It is found to be homeomorphic to $\mathbb{Q}$, with a compact completion homeomorphic to the Cantor set. It has a natural place in a family of topologies on $\mathbb{Z}$, which includes the $p$-adics, and one in which the set of rational primes $\mathbb{P}$ is dense. Examples from number theory are given, including the primes and squares, Fermat numbers, Fibonacci numbers and $k$-free numbers.

Given a smooth projective curve $C$ of positive genus $g$, Torelli's theorem asserts that the pair $\left( J\left( C \right),\,{{W}^{g-1}} \right)$ determines $C$. We show that the theorem is true with ${{W}^{g-1}}$ replaced by ${{W}^{d}}$ for each $d$ in the range $1\,\le \,d\,\le \,g\,-\,1$.

Le problème de Jung-Nagata $\left( cf.\,\left[ \text{J} \right],\,\left[ \text{N} \right] \right)$ consiste à savoir s'il existe des automorphismes de $k\left[ x,\,y,\,z \right]$ qui ne sont pas modérés. Nous proposons une approche nouvelle de cette question, fondée sur l'utilisation de la théorie des automates et du polygone de Newton. Cette approche permet notamment de généraliser de façon significative les résultats de $\left[ \text{A} \right]$.

Let $V$ be an analytic variety in some open set in ${{\mathbb{C}}^{n}}$ which contains the origin and which is purely $k$-dimensional. For a curve $\gamma $ in ${{\mathbb{C}}^{n}}$, defined by a convergent Puiseux series and satisfying $\gamma (0)\,=\,0$, and $d\,\ge \,1$, define ${{V}_{t}}\,:=\,{{t}^{-d}}\,\left( V\,-\,\gamma \left( t \right) \right)$. Then the currents defined by ${{V}_{t}}$ converge to a limit current ${{T}_{\gamma ,d}}\left[ V \right]$ as $t$ tends to zero. ${{T}_{\gamma ,d}}\left[ V \right]$ is either zero or its support is an algebraic variety of pure dimension $k$ in ${{\mathbb{C}}^{n}}$. Properties of such limit currents and examples are presented. These results will be applied in a forthcoming paper to derive necessary conditions for varieties satisfying the local Phragmén-Lindelöf condition that was used by Hörmander to characterize the constant coefficient partial differential operators which act surjectively on the space of all real analytic functions on ${{\mathbb{R}}^{n}}$.

Let ${{\mathcal{H}}_{n}}$ be the real linear space of $n\,\times \,n$ complex Hermitian matrices. The unitary (similarity) orbit $\mathcal{U}\left( C \right)$ of $C\,\in \,{{\mathcal{H}}_{n}}$ is the collection of all matrices unitarily similar to $C$. We characterize those $C\,\in \,{{\mathcal{H}}_{n}}$ such that every matrix in the convex hull of $\mathcal{U}\left( C \right)$ can be written as the average of two matrices in $\mathcal{U}\left( C \right)$. The result is used to study spectral properties of submatrices of matrices in $\mathcal{U}\left( C \right)$, the convexity of images of $\mathcal{U}\left( C \right)$ under linear transformations, and some related questions concerning the joint $C$-numerical range of Hermitian matrices. Analogous results on real symmetric matrices are also discussed.

In this paper, we consider the set $\text{S}=a\left( {{e}^{X}}K{{e}^{Y}} \right)$ where $a\left( g \right)$ is the abelian part in the Cartan decomposition of $g$. This is exactly the support of the measure intervening in the product formula for the spherical functions on symmetric spaces of noncompact type. We give a simple description of that support in the case of $\text{SL}\left( 3,\,\mathbf{F} \right)\,\text{where}\,\mathbf{F}\,=\,\mathbf{R},\,\mathbf{C}\,\text{or}\,\mathbf{H}$. In particular, we show that $\text{S}$ is convex.

We also give an application of our result to the description of singular values of a product of two arbitrary matrices with prescribed singular values.