Symmetries of theq-difference heat equation

The symmetry operators of aq-difference analog of the heat equation in one space dimension are determined. They are seen to generate aq-deformation of the semidirect product of sl(2, ) with the three-dimensional Weyl algebra. It is shown that this algebraic structure is preserved if differentq-analogs of the heat equation are considered. The separation of variables associated to the dilatation symmetry is performed and solutions involving discreteq-Hermite polynomials are obtained.     

A stochastic posterior Schrödinger equation for counting nondemolition measurement

A stochastic model of the continuous counting nondemolition measurement of photons emitted by an excited atom in a quantum electromagnetic field is given. It is proved that the posterior dynamics of such an atom is described by a new nonlinear stochastic wave equation showing the relaxation of the atom to its ground state due to the photon emission.     

Symmetries and half-sided modular inclusions of von Neumann algebras

LetN, be a von Neumann algebras on a Hilbert space , a common cyclic and separating vector. Assume to be cyclic and also separating forN . Denote by , _N , _N the modular operators to (, ), (N, ), resp (N , ). Assume now ^-it N ^it N for allt 0. (Such type of inclusions ((N U, ) , ) are called half-sided modular.) Then the modular groups ^it , _N ^ir , _N ^is ,t, r, s generate a unitary representation of the group S1(2, )/Z ₂ of positive energy.Another result is related to two half-sided modular inclusions (₁ , ) and (₂ , ). Under proper conditions the three modular groups ^it , ₁ ^ir , ₂ ^is ,t, r, s generate the three-dimensional subgroup of O(2, 1) of two commuting translations and the Lorentz transformation.Partly supported by the DFG, SFB 288 Differentialgeometrie und Quantenphysik.     

Symmetries of massless Dirac equations and supersymmetric quantum mechanics

It is shown how symmetries of Dirac equations can be used to obtain constants of motion for nonrelativistic supersymmetric quantum Hamiltonians. In particular, conserved supercharges are found for a spin-1/2 particle in the field of a dyon which yield under anticommutation the generalized Runge-Lenz symmetry of the system.This work is supported in part through funds provided by the Natural Sciences and Engineering Research Council (NSERC) of Canada and the Fonds FCAR of the Quebec Ministry of Education.     

Canonical quantization of the Bateman-Morse-Feshbach damped oscillator

The Bateman-Morse-Feshbach classical formulation of the damped oscillator is canonically quantized. The spectrum of the Hamiltonian is given. It is shown that the wavefunctions behave asymptotically as a superposition of damped oscillators when their initial values belong to an appropriately-selected dense subset of the Hilbert space.partially supported by U.S. Army Grant DAAL03-87-K-0110.Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy.     

KMS states for the Weyl algebra

We consider the possible automorphism groups for the Weyl algebra overR, resp.T, and classify those for which KMS states, unique or not unique, exist.     

Finite-time deviations from exponential decay in the Weisskopf-Wigner model of spontaneous emission

For the first time to the authors' knowledge, a mathematically rigorous method is used for treating finite-time deviations from the exponential decay in the case of spontaneous Lyman- transition in a two-level hydrogenic atom. In the so-called Weisskopf-Wigner model (where the rotating-wave approximation is implied), finite-time deviations with a rigorous validity range, based on accurate error estimations, are derived.     

Finite-time deviations from exponential decay of dipole-moment expectation values in the case of spontaneous emission

For the first time, to the authors' knowledge, a mathematically rigorous method is used for obtaining finite-time deviations from the exponential decay of the dipole-moment expectation values in the case of spontaneous Lyman- transition in a two-level hydrogenic atom. In calculations counterrotating terms, yielding the frequency shift (Lamb shift) within the scope of the two-level model, are taken into account.     

The two-parameter deformation of the supergroup GL(1|1), its differential calculus and its Lie algebra

We construct a right-invariant differential calculus on the quantum supergroup GL _q,s (1|1) and we show that its quantum Lie algebra with comultiplication is isomorphic to that which we obtain using the Reshetikhin-Takhtajan-Faddeev approach.     

Z 3-Graded exterior differential calculus and gauge theories of higher order

We present a possible generalization of the exterior differential calculus, based on the operator d such that d³=0, but d²0. The entities dx ⁱ and d² x ^k generate an associative algebra; we shall suppose that the products dx ⁱ dx ^k are independent of dx ^k dx ⁱ , while theternary products will satisfy the relation: dx ⁱ dx ^k dx ^m =jdx ^k dx ^m dx ⁱ =j ²dx ^m dx ^m dx ⁱ dx ^k , complemented by the relation dx ⁱ d² x ^k =jd² x ^k dx ⁱ , withj:=e^2i/3.We shall attribute grade 1 to the differentials dx ⁱ and grade 2 to the second differentials d² x ^k ; under the associative multiplication law the grades add up modulo 3.We show how the notion ofcovariant derivation can be generalized with a 1-formA so thatD:=d+A, and we give the expression in local coordinates of thecurvature 3-form defined as :=d² A+d(A ²)+AdA+A ³.Finally, the introduction of notions of a scalar product and integration of theZ ₃-graded exterior forms enables us to define the variational principle and to derive the differential equations satisfied by the 3-form . The Lagrangian obtained in this way contains the invariants of the ordinary gauge field tensorF _ik and its covariant derivativesD _i F _km .     

Covariantising the Beltrami equation in W-gravity

Recently, certain higher-dimensional complex manifolds were obtained by S. Govindarajan [1] by associating a higher dimensional uniformisation to the generalised Teichmüller spaces of Hitchin. The extra dimensions are provided by the times of the generalised KdV hierarchy. In this Letter, we complete the proof that these manifolds provide the analog of superspace for W-gravity and that W-symmetry linearises on these spaces. This is done by explicitly constructing the relationship between the Beltrami differentials which naturally occur in the higher-dimensional manifolds and the Beltrami differentials which occur in W-gravity. This also resolves an old puzzle regarding the relationship between KdV flow. and W-diffeomorphisms.Dedicated to the memory of Claude Itzykson.     

A canonical form of an algebraic equation for genus 3 Reimann surfaces

We propose a canonical form of an algebraic equation describing each conformal equivalence class of genus 3 nonhyperelliptic Riemann surface. The equation yields a 3-sheet covering with nine ramification points. This result can have applications in string theory and in the theory of solvable models in statistical mechanics.     

The quantum Sturm-Liouville equation,quantum resolvent,quantum integrals,and quantum KdV: The fast decrease case

We construct quantum operators solving the quantum versions of the Sturm-Liouville equation and the resolvent equation, and show the existence of conserved currents. The construction depends on the following input data: the basic quantum field O(k) and the regularization.     

Differential algebras andD-modules in super toda lattice hierarchy

A new super Toda lattice hierarchy is proposed and formulated in the language of differential algebra. AD-module structure is shown to exist behind this nonlinear system and to play the same role as a similarD-module for the super KP hierarchy. From the structure of thisD-module, one can indeed see a direct connection with a set of affine coordinates on an infinite-dimensional super Grassmannian manifold. These affine coordinates are the basic ingredients of an intrinsic construction of functions as well as symmetries.     

A class of solutions of the dispersionless KP equation

We construct a class of (complex-valued) solutions to the dispersionless KP equation using a meromorphic function on a plane algebraic curve as a variable dependent on suitable Abelian integrals.     

The B-quadrilateral lattice,its transformations and the algebro-geometric construction

The B-quadrilateral lattice (BQL) provides geometric interpretation of Miwa’s discrete BKP equation within the quadrialteral lattice (QL) theory. After discussing the projective-geometric properties of the lattice we give the algebro-geometric construction of the BQL emphasizing the role of Prym varieties and the corresponding theta functions. We also present the reduction of the vectorial fundamental transformation of the QL to the BQL case.     

On the Bardeen-Cooper-Schrieffer integral equation in the theory of superconductivity

The Bardeen-Cooper-Schrieffer integral equation with a positive kernel is studied in full generality. It is shown that, there exists a unique finite transition temperature, T _c so that, if T _c ,the equation possesses a positive solution, representing the onset of the superconducting phase, while if T>T _c ,the only solution of the equation is the trivial one, indicating the occurrence of the normal phase. Moreover, it is demonstrated that such a positive solution may be approximated by a sequence of solutions of the equation restricted on bounded domains. This latter result provides a useful computational scheme for the problem.     

Convergence of Logarithmic Quantum Mechanics to the Linear One

We study the nonlinear logarithmic Schrödinger equation in three dimensions. We establish the existence of the solutions of general quasi-linear Schrödinger equations. Finally, we show the convergence of the logarithmic quantum mechanics to the linear regime.