On Rationality of the Cogrowth Series

The cogrowth series of a group depends on the presentation of the group. We show that the cogrowth series of a non-empty presentation is a rational function not equal to 1 if and only if is finite. Except for the trivial group, this property is independent of presentation.

     

On Rationality of W-algebras

We study the problem of classification of triples ( $ \mathfrak{g} $ ; f; k), where g is a simple Lie algebra, f its nilpotent element and k ∈ $ \mathbb{C} $ , for which the simple W-algebra W _k ( $ \mathfrak{g} $ ; f) is rational.     

关于Nielson Zeta函数的有理性

Ａ．Ｌ．Ｆｅｌ＇ｓｈｔｙｎ和Ｖ．Ｂ．Ｐｉｌｙｕｇｉｎａ定义了Ｎｉｅｌｓｏｎｚｅｔａ函数并证明关于其有理性的一些结果，本文改进了他们的一些结果。     

On the Spectrum of Invertible Semi-hyponormal Operators

It is known that for a semi-hyponormal operator, the spectrum of the operator is equal to the union of the spectra of the general polar symbols of the operator. The original proof of this theorem involves the so-called singular integral model. The purpose of this paper is to give a different proof of the same theorem for the case of invertible semi-hyponormal operators without using the singular integral model.      

On the Prime Spectrum of X-Injective Modules

Let R be a commutative ring and M an R-module. The purpose of this article is to introduce a new class of modules over R called X-injective R-modules, where X is the prime spectrum of M. This class contains the family of top modules and that of weak multiplication modules properly. In this article our concern is to extend the properties of multiplication, weak multiplication, and top modules to this new class of modules. Furthermore, for a top module M, we study some conditions under which the prime spectrum of M is a spectral space for its Zariski topology.     

On the Spectrum of Degenerate Operator Equations

We study the distribution in the complex plane of the spectrum of the operator , generated by the closure in of the operation originally defined on smooth functions with values in a Hilbert space satisfying the Dirichlet conditions . Here and A is a model operator acting in . Criterial conditions on the parameter for the eigenfunctions of the operator to form a complete and minimal system as well as a Riesz basis in the Hilbert space H are given.     

On the Spectrum of the One-Particle Density Matrix

Functional Analysis and Its Applications - The one-particle density matrix $$\gamma(x, y)$$ is one of the key objects in quantum-mechanical approximation schemes. The self-adjoint operator...     

On the Spectrum of the Generalised Petersen Graphs

We show that the gap between the two greatest eigenvalues of the generalised Petersen graphs P(n, k) tends to zero as \(n \rightarrow \infty \). Moreover, we provide explicit upper bounds on the size of this gap. It follows that these graphs have poor expansion properties for large values of n. We also show that there is a positive proportion of the eigenvalues of P(n, k) tending to three.     

On the Gap in the Spectrum of the Translations

The spectrum of the translations in local quantum field theory will be analyzed in order to show that in a positive energy representation without vacuum vector and with lowest mass m₁ there is no gap in the spectrum which is larger than 2m₁. In particular in a zero mass representation there is no hole at all. These results are obtained with methods of analytic functions of several complex variables.     

On the Laplacian Spectrum and Walk-regular Hypergraphs

We use the generalization of the Laplacian matrix to hypergraphs to obtain several spectral-like results on hypergraphs. For instance, we obtain upper bounds on the eccentricity and the excess of any vertex of hypergraphs. We extend to the case of hypergraphs the concepts of walk regularity and spectral regularity, showing that all walk-regular hypergraphs are spectrally-regular. Finally, we obtain an upper bound on the mean distance of walk-regular hypergraphs that involves all the Laplacian spectrum.     

On the Laplacian Spectrum and Walk-regular Hypergraphs

We use the generalization of the Laplacian matrix to hypergraphs to obtain several spectral-like results on hypergraphs. For instance, we obtain upper bounds on the eccentricity and the excess of any vertex of hypergraphs. We extend to the case of hypergraphs the concepts of walk regularity and spectral regularity, showing that all walk-regular hypergraphs are spectrally-regular. Finally, we obtain an upper bound on the mean distance of walk-regular hypergraphs that involves all the Laplacian spectrum.     

On the Spectrum of the Product of Closed Operators

In this note we study the connection between the spectra of the products AB and BA of unbounded closed operators A and B acting in Banach spaces. Under the condition that the resolvent sets of these products are not empty we show that the spectra of AB and BA coincide away from zero and prove the commutation relation 𝕀 . Further, we prove statements concerning the relationship between the spectra of the operator AB and the block operator matrix .     

On the Absolutely Continuous Spectrum of Dirac Operator

Abstract

We prove that the massless Dirac operator in ?³ with long-range potential has an a.c. spectrum which fills the whole real line. The Dirac operators with matrix-valued potentials are considered as well.     

On the Spectrum of a Non-Self-Adjoint Quasiperiodic Operator

Doklady Mathematics - We study the operator $$\mathcal{A}$$ acting in $${{l}^{2}}(\mathbb{Z})$$ by the formula $${{(\mathcal{A}u)}_{l}} = {{u}_{{l + 1}}} + {{u}_{{l - 1}}} + \lambda {{e}^{{ - 2\pi...     

On the Discrete Spectrum of Generalized Quantum Tubes

The spectrum (of the Dirichlet Laplacian) of non-compact, non-complete Riemannian manifolds is much less understood than their compact counterparts. In particular it is often not even known whether such a manifold has any discrete spectra. In this article, we will prove that a certain type of non-compact, non-complete manifold called the quantum tube has non-empty discrete spectrum. The quantum tube is a tubular neighborhood built about an immersed complete manifold in Euclidean space. The terminology of “quantum” implies that the geometry of the underlying complete manifold can induce discrete spectra – hence quantization. We will show how the Weyl tube invariants appear in determining the existence of discrete spectra. This is an extension and generalization, on the geometric side, of the previous work of the author on the “quantum layer.”     

On the Cycle Spectrum of Cubic Hamiltonian Graphs

We prove lower bounds on the number of different cycle lengths of cubic Hamiltonian graphs that do not contain a fixed subdivision of a claw as an induced subgraph.     

On the Spectrum of the Resonant Quantum Kicked Rotor

It is proven that none of the bands in the quasi-energy spectrum of the Quantum Kicked Rotor is flat at any primitive resonance of any order. Perturbative estimates of bandwidths at small kick strength are established for the case of primitive resonances of prime order. Different bands scale with different powers of the kicking strength, due to degeneracies in the spectrum of the free rotor.     

On the Spectrum of Cartesian Powers of Classical Automorphisms

We prove the following statement: the set of all essential spectral multiplicities of (n times) is on for Chacon transformations T, or, equivalently, the operator T(ⁿ) has a simple spectrum on the subspace C _Sim of all functions that are invariant with respect to permutations of the coordinates. As an immediate consequence of this fact, we have the disjointness of all convolution powers of the spectral measure for Chacon transformations. If n=2, then T× T has a homogeneous spectrum of multiplicity 2 on , i.e., this is a solution of Rokhlin's problem for Chacon transformations. Similar statements are considered for other classical automorphisms.