Algebra with Quadratic Commutation Relations for an Axially Perturbed Coulomb–Dirac Field

The motion of a particle in the field of an electromagnetic monopole (in the Coulomb–Dirac field) perturbed by an axially symmetric potential after quantum averaging is described by an integrable system. Its Hamiltonian can be written in terms of the generators of an algebra with quadratic commutation relations. We construct the irreducible representations of this algebra in terms of second-order differential operators; we also construct its hypergeometric coherent states. We use these states in the first-order approximation with respect to the perturbing field to obtain the integral representation of the eigenfunctions of the original problem in terms of solutions of the model Heun-type second-order ordinary differential equation and present the asymptotic approximation of the corresponding eigenvalues.     

Non-Lie top tunneling and quantum bilocalization in planar Penning trap

We describe how a top-like quantum Hamiltonian over a non-Lie algebra appears in the model of the planar Penning trap under the breaking of its axial symmetry (inclination of the magnetic field) and tuning parameters (electric voltage, magnetic field strength and inclination angle) at double resonance. For eigenvalues of the quantum non-Lie top, under a specific variation of the voltage on the trap electrode, there exists an avoided crossing effect and a corresponding effect of bilocalization of quantum states on pairs of closed trajectories belonging to common energy levels. This quantum tunneling happens on the symplectic leaves of the symmetry algebra, and hence it generates a tunneling of quantum states of the electron between the 3D-tori in the whole 6D-phase space. We present a geometric formula for the leading term of asymptotics of the tunnel energy-splitting in terms of symplectic area of membranes bounded by invariantly defined instantons.     

Finitely Correlated Pure States

We study a w*-dense subset of the translation invariant states on an infinite tensor product algebra , where is a matrix algebra. These "finitely correlated states" are explicitly constructed in terms of a finite dimensional auxiliary algebra and a completely positive map : → . We show that such a state ω is pure if and only if it is extremal periodic and its entropy density vanishes. In this case the auxiliary objects and are uniquely determined by ω, and can be expressed in terms of an isometry between suitable tensor product Hilbert spaces.     

On the cobordism and commutative monoid with cancellation approaches to conformal field theory

In the late 1980s, Graeme Segal axiomatized conformal field theory in terms of a cobordism category. In that same preprint he outlined a more symmetric trace approach, which was recently rigorized in terms of pseudo algebras over a 2-theory. In this paper, we treat the cobordism approach in the pseudo algebra context. We introduce a new algebraic structure on a bicategory, called a pseudo 2-algebra over a theory, as a means of comparison for the two approaches. The main result states that the 2-category of pseudo algebras over a fixed 2-theory is biequivalent to the 2-category of pseudo 2-algebras over a fixed theory in certain situations.     

Why is quantum physics based on complex numbers?

The modern quantum theory is based on the assumption that quantum states are represented by elements of a complex Hilbert space. It is expected that in future quantum theory the number field will not be postulated but derived from more general principles. We consider the choice of the number field in a quantum theory based on a finite field. We assume that the symmetry algebra is the finite field analog of the de Sitter algebra so(1,4) and consider spinless irreducible representations of this algebra. It is shown that the finite field analog of complex numbers is the minimal extension of the residue field modulo p for which the representations are fully decomposable.     

Algebra with polynomial commutation relations for the Zeeman-Stark effect in the hydrogen atom

We study the Zeeman-Stark effect for the hydrogen atom in crossed homogeneous electric and magnetic fields. A nonhomogeneous perturbing potential can also be present. If the crossed fields satisfy some resonance relation, then the degeneration in the resonance spectral cluster is removed only in the second-order term of the perturbation theory. The averaged Hamiltonian in this cluster is expressed in terms of generators of some dynamical algebra with polynomial commutation relations; the structure of these relations is determined by a pair of coprime integers contained in the resonance ratio. We construct the irreducible hypergeometric representations of this algebra. The averaged spectral problem in the irreducible representation is reduced to a second-or third-order ordinary differential equation whose solutions are model polynomials. The asymptotic behavior of the solution of the original problem concerning the Zeeman-Stark effect in the resonance cluster is constructed using the coherent states of the dynamical algebra. We also describe the asymptotic behavior of the spectrum in nonresonance clusters, where the degeneration is already removed in the first-order term of the perturbation theory.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 142, No. 3, pp. 530–555, March, 2005.     

Sufficiency and strong commutants in quantum probability theory

A probability algebra (A, *, ω) consisting of a^*algebraA with a faithful state ω provides a framework for an unbounded noncommutative probability theory. A characterization of symmetric probability algebra is obtained in terms of an unbounded strong commutant of the left regular representation ofA. Existence of coarse-graining is established for states that are absolutely continuous or continuous in the induced topology. Sufficiency of a^*subalgebra relative to a family of states is discussed in terms of noncommutative Radon-Nikodym derivatives (a form of Halmos-Savage theorem), and is applied to couple of examples (including the canonical algebra of one degree of freedom for Heisenberg commutation relation) to obtain unbounded analogues of sufficiency results known in probability theory over a von Neumann algebra.     

Identities of the Model Algebra of Multiplicity 2

We construct an additive basis of the free algebra of the variety generated by the model algebra of multiplicity 2 over an infinite field of characteristic not 2 and 3. Using the basis we remove a restriction on the characteristic in the theorem on identities of the model algebra (previously the same was proved in the case of characteristic 0). In particular, we prove that the kernel of the relatively free Lie-nilpotent algebra of index 5 coincides with the ideal of identities of the model algebra of multiplicity 2.     

On Isotypic Decompositions for Non-Semisimple Hopf Algebras

In this paper we study the isotypic decomposition of the regular module of a finite-dimensional Hopf algebra over an algebraically closed field of characteristic zero. For a semisimple Hopf algebra, the idempotents realizing the isotypic decomposition can be explicitly expressed in terms of characters and the Haar integral. In this paper we investigate Hopf algebras with the Chevalley property, which are not necessarily semisimple. We find explicit expressions for idempotents in terms of Hopf-algebraic data, where the Haar integral is replaced by the regular character of the dual Hopf algebra. For a large class of Hopf algebras, these are shown to form a complete set of orthogonal idempotents. We give an example which illustrates that the Chevalley property is crucial.

     

Rigorous Formulation of a 2D Conformal Model in the Fock–Krein Space: Construction of the Global Op J *-Algebra of Fields and Currents

We use the formalism of the 2D massless scalar field model in an indefinite space of the Fock–Krein type as a basis for constructing a rigorous formulation of 2D quantum conformal theories. We show that the sought construction is a several-stage procedure whose central block is the construction of a new type of representation of the Virasoro algebra. We develop the first stage of this procedure, which is to construct a special global algebra of fields and currents generated by exponential generators. We obtain a system of commutation relations for the Wick-squared currents used in the definition of the Virasoro generators. We prove the existence of Wick exponentials of the current given by operator-valued generalized functions; the sought global algebra is rigorously defined as the algebra of current and field, Wick and normal exponentials on a common dense invariant domain in a Fock–Krein space.     

The ring of physical states in the <Emphasis Type="Italic">M</Emphasis>(2, 3) minimal Liouville gravity

We consider the M(2, 3) minimal Liouville gravity, whose state space in the gravity sector is realized as irreducible modules of the Virasoro algebra. We present a recursive construction for BRST cohomology classes based on using an explicit form of singular vectors in irreducible modules of the Virasoro algebra. We find a certain algebra acting on the BRST cohomology space and use this algebra to find the operator algebra of physical states.     

Equilibrium states on the Cuntz–Pimsner algebras of self-similar actions

We consider a family of Cuntz–Pimsner algebras associated to self-similar group actions, and their Toeplitz analogues. Both families carry natural dynamics implemented by automorphic actions of the real line, and we investigate the equilibrium states (the KMS states) for these dynamical systems. We find that for all inverse temperatures above a critical value, the KMS states on the Toeplitz algebra are given, in a very concrete way, by traces on the full group algebra of the group. At the critical inverse temperature, the KMS states factor through states of the Cuntz–Pimsner algebra; if the self-similar group is contracting, then the Cuntz–Pimsner algebra has only one KMS state. We apply these results to a number of examples, including the self-similar group actions associated to integer dilation matrices, and the canonical self-similar actions of the basilica group and the Grigorchuk group.     

Spinor bose condensate and the su(1,1) Richardson model

We consider a dilute gas of trapped bosonic atoms with hyperfine spin F = 1 that interacts with the classical laser field. In the single mode approximation, the Hamiltonian of the model may be expressed in terms of the boson realization of the su(1, 1) algebra. The model is solved by the Algebraic Bethe Ansatz approach. Bibliography: 15 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 317, 2004, pp. 43–56.     

Representation of exact and semiclassical eigenfunctions via coherent states. Hydrogen atom in a magnetic field

Global formulas for eigenfunctions and solutions to the Cauchy problem, including the path integral representation, are obtained using the coherent states technique. The reduction of coherent states via symmetry groups is studied for a transformation from Bessel to hypergeometric states. The eigenfunctions of the Hamiltonian for the hydrogen atom in a homogeneous magnetic field are expressed in terms of Bessel coherent states. For a small field, after quantum averaging, the Hamiltonian is represented in terms of generators with quadratic commutation relations. The irreducible representations of this quadratic algebra are realized on hypergeometric states. The notion of deformed hypergeometric states is also introduced for this quadratic algebra as an analog of squeezed Gaussian packets of the Heisenberg algebra. The asymptotic equations of eigenfunctions with respect to a small field and a large leading quantum number are derived using these states and their deaveraging. Some explicit formulas for the Zeeman splitting of the spectrum are obtained up to the fourth order with respect to the field, as well as for lower and upper levels in the cluster, including the case of incidence on the center.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 108, No. 3, pp. 339–387, September, 1996.     

The form factor program: A review and new results,the nested <Emphasis Type="Italic">SU</Emphasis>(<Emphasis Type="Italic">N</Emphasis>) off-shell Bethe ansatz and the 1/<Emphasis Type="Italic">N</Emphasis> expansion

The purpose of the “bootstrap program” for integrable quantum field theories in 1+1 dimensions is to construct a model explicitly in terms of its Wightman functions. We illustrate this program here mainly in terms of the SU(N) Gross-Neveu model. We construct the nested off-shell Bethe ansatz for an SU(N) factoring S-matrix and consider the problem of how to sum over intermediate states in the short-distance limit of the two-point Wightman function for the sinh-Gordon model. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 155, No. 1, pp. 13–24, April, 2008.     

Denominators in cluster algebras of affine type

The Fomin–Zelevinsky Laurent phenomenon states that every cluster variable in a cluster algebra can be expressed as a Laurent polynomial in the variables lying in an arbitrary initial cluster. We give representation-theoretic formulas for the denominators of cluster variables in cluster algebras of affine type. The formulas are in terms of the dimensions of spaces of homomorphisms in the corresponding cluster category, and hold for any choice of initial cluster.     

Deformed supersymmetry,q-oscillator algebra, and related scattering problems in quantum mechanics

We describe extensions of the supersymmetric quantum mechanics (SSQM) (in one dimension) which are characterized by deformed algebras. The supercharges involving higher-order derivatives are introduced, leading to a deformed algebra which incorporates a higher-order polynomial of the Hamiltonian. When supplementing them with dilatations, one finds the class of q-deformed SUSY systems. For a special choice of q-self-similar potentials, the energy spectrum is (partially) generated by the q-oscillator algebra. In contrast to the standard harmonic oscillators, these systems exhibit a continuous spectrum. We investigate the scattering problem in the q-deformed SSQM and introduce the notion of self-similarity in the momentum space for scattering data. An explicit model for the scattering amplitude of a q-oscillator is constructed in terms of a hypergeometric function. This model corresponds to a reflectionless potential with infinitely, many bound states. A general method of realization of the q-oscillator algebra on the space of wave functions for a one-dimensional Schrödinger Hamiltonian is developed. It shows the existence of non-Fock irreducible representations associated with the continuous part of the spectrum and directly related to the deformation. Bibliography: 24 titles.     

On Maximal Diagonalizable Lie Subalgebras of the First Hochschild Cohomology

Let A be a basic connected finite dimensional algebra over an algebraically closed field, with ordinary quiver without oriented cycles. Given a presentation of A by quiver and admissible relations, Assem and de la Peña have constructed an embedding of the space of additive characters of the fundamental group of the presentation into the first Hochschild cohomology group of A. We compare the embeddings given by the different presentations of A. In some situations, we characterise the images of these embeddings in terms of (maximal) diagonalizable subalgebras of the first Hochschild cohomology group (endowed with its Lie algebra structure).     

On the quiver with relations of a quasitilted algebra and applications

In this paper we discuss, in terms of quiver with relations, su?cient and necessary conditions for an algebra to be a quasitilted algebra. We start with an algebra with global dimension at most two and we give a su?cient condition to be a quasitilted algebra. We show that this condition is not necessary. In the case of a strongly simply connected schurian algebra, we discuss necessary conditions, and combining both types of conditions, we are able to analyze if some given algebra is quasitilted. As an application we obtain the quiver with relations of all the tilted and cluster tilted algebras of Dynkin type E_p.     

A dynamical systems approach to the Kadison-Singer problem

In these notes we develop a link between the Kadison-Singer problem and questions about certain dynamical systems. We conjecture that whether or not a given state has a unique extension is related to certain dynamical properties of the state. We prove that if any state corresponding to a minimal idempotent point extends uniquely to the von Neumann algebra of the group, then every state extends uniquely to the von Neumann algebra of the group. We prove that if any state arising in the Kadison-Singer problem has a unique extension, then the injective envelope of a C*-crossed product algebra associated with the state necessarily contains the full von Neumann algebra of the group. We prove that this latter property holds for states arising from rare ultrafilters and δ-stable ultrafilters, independent, of the group action and also for states corresponding to non-recurrent points in the corona of the group.