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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 30-61 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A perturbation theory for Schrödinger and heat equations that is based on phase-space variables is developed. The Dyson series representing the evolution kernel is described in terms of two basic classical quantities: the free classical motion along flat space geodesics and the Green function for the Jacobi operator in phase space. Further, for problems with Abelian interactions it is demonstrated that the perturbation theory may be summed to all orders yielding an exponentiated connected graph description for the evolution kernel. Connected graph representations provide an efficient method of constructing various semiclassical approximations wherein expansion coefficients are directly determined by explicit cluster integrals. This type of application is discussed for the case of Schrödinger and heat equations with external electromagnetic fields. Detailed expressions for coefficients are obtained for both the gauge invariant large mass expansion as well as the short time Schwinger–DeWitt expansion. Finally it is shown how to apply this phase-space method so that it incorporates a recently proposed covariant perturbation theory. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 26 (1985), S. 2796-2802 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A local spectral sum rule for nonrelativistic scattering in two dimensions is derived for the potential class v∈L4/3 (R2). The sum rule relates the integral over all scattering energies of the trace of the time-delay operator for a finite region Σ⊆R2 to the contributions in Σ of the pure point and singularly continuous spectra.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 26 (1985), S. 753-768 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: For quantum systems in R3 defined by a Hamiltonian H given as the sum of the negative Laplacian perturbed by a real-valued potential v(x), the large time behavior of the fundamental solution of the time-dependent Schrödinger equation is investigated. For a suitably restricted class of potentials that have algebraic decay as ||x||→∞, the continuous spectrum portion of the fundamental solution is characterized by an asymptotic expansion as t→±∞, which is uniform in compact subsets of R3×R3. These results are then applied to derive the large energy asymptotic expansions of the spectral kernel associated with H.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 28 (1987), S. 103-123 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The quantum evolution of an N-body system of particles that mutually interact through scalar fields and couple to an arbitrary external electromagnetic field is rigorously described. Both operator and kernel valued solutions to the evolution problem are found. Based upon a particular realization of the Dyson expansion, a convergent series representation of the propagator (the kernel of the Schrödinger time evolution operator) is obtained. The basic approach is to embed the quantum evolution problem in the larger class of evolution problems that result if mass is allowed to be complex. Quantum evolution with real mass is considered to be the boundary value of the complex mass evolution problem. The constructive representation of the propagator is determined for the class of analytic scalar and vector fields that are given as Fourier transforms of time-dependent scalar and vector-valued measures.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 26 (1985), S. 453-464 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Suppose H is the Hamiltonian that generates time evolution in an N-body, spin-dependent, nonrelativistic quantum system. If r is the total number of independent spin components and the particles move in three dimensions, then the Hamiltonian H is an r×r matrix operator given by the sum of the negative Laplacian −Δx on the (d=3N)-dimensional Euclidean space Rd plus a Hermitian local matrix potential W(x). Uniform higher-order asymptotic expansions are derived for the time-evolution kernel, the heat kernel, and the resolvent kernel. These expansions are, respectively, for short times, high temperatures, and high energies. Explicit formulas for the matrix-valued coefficient functions entering the asymptotic expansions are determined. All the asymptotic expansions are accompanied by bounds for their respective error terms. These results are obtained for the class of potentials defined as the Fourier image of bounded complex-valued matrix measures. This class is suitable for the N-body problem since interactions of this type do not necessarily decrease as ||x||→∞. Furthermore, this Fourier image class also contains periodic, almost periodic, and continuous random potentials. The method employed is based upon a constructive series representation of the kernels that define the analytic semigroup {e−zH||Re z〉0}. The asymptotic expansions obtained are valid for all finite coordinate space dimensions d and all finite vector space dimensions r, and are uniform in Rd×Rd. The order of expansion is solely a function of the smoothness properties of the local potential W(x).
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 27 (1986), S. 88-99 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A combinatorial method is used to construct solutions of the Hamilton–Jacobi equation. An exact expression for Hamilton's principal function S is obtained for classical systems of finitely many particles interacting via a certain class of time-dependent potentials. If x, p, and t are the position, momentum, and time variables for N point particles of mass m, it is shown that Hamiltonians of the form H(x,p,t)=(1/2m)p2+v(x,t) have complete integrals S that are analytic functions of the inverse mass parameter m−1 in a punctured disk about the origin. If v(x,t) is bounded, C∞ in the x variable, and has controlled x-derivative growth, then the coefficients of the Laurent expansion of S about m−1=0 may be expressed in terms of gradient structures associated with tree graphs. This series expansion for S(x,t; y,t0) converges absolutely, and uniformly for all x, y for time displacements ||t−t0||〈T≡2K−1(m/eU)1/2, where K and U are bounds associated with the space derivatives of the potential. For ||t−t0||〈T, the classical path (from any initial space-time configuration y,t0 to any final configuration x,t) induced by S is unique, passes through no conjugate points, and furnishes the action functional with a strong minimum. The local solution S given above may be used to obtain the classical trajectories for arbitrarily large times.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 30 (1989), S. 420-432 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The energy-dependent trace-class time-delay operator associated with the transit time of a scattering system through a finite space region Σ⊆R2 is used to define a local (Σ-dependent) version of the Krein spectral shift function. If the region Σ is a disk of radius r, it is proved that as r→∞ the local spectral shift function converges, for almost all energies, to the original spectral shift function of Krein. This result continues to be valid for systems exhibiting zero-energy resonance behavior.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 29 (1988), S. 642-659 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The large mass asymptotics of the quantum evolution problem for a system of charged particles that mutually interact through scalar fields and couple to an arbitrary time-varying external electromagnetic field is rigorously described. If K(x,t; y,s;m) denotes the coordinate space propagator (time evolution kernel) of this system, the singular perturbation behavior of K as mass m→∞ is expressed in terms of a gauge invariant asymptotic expansion. In terms of the external fields and interparticle interactions, this expansion provides a nonperturbative approximation for the propagator K that is valid for all particle coordinates x, y and for finite time displacements t−s. For the class of analytic scalar and vector fields that are defined as Fourier transforms of time-dependent measures, the existence of this asymptotic series for K in powers of (m)−1 is established for both real and complex masses. Explicit bounds for the error term are obtained and a manifestly gauge invariant transport recurrence relation is derived that uniquely determines all the coefficient functions of the asymptotic series. The small time asymptotic expansion of K is shown to be embedded within the large mass expansion.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 938-955 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A singular perturbation expansion of solutions to the Schrödinger initial value problem is constructed using an approximate propagator. For a nonrelativistic quantum system interacting with time-dependent external electromagnetic fields, this approximate propagator defines a gauge invariant semiclassical expansion that is realized by large mass scaling. The asymptotic nature of this approximation is established by constructing error estimates that bound the Hilbert space norm difference between the exact and approximate evolved states. The maximum order of the approximation is determined explicitly as a function of the number of derivatives supported by the scalar and vector potentials. The asymptotic expansion is obtained when the configuration space Ω=Rd, and also for problems where Ω is a proper subset of Rd and the self-adjoint Hamiltonian is defined using a supplementary boundary condition—typically Dirichlet or periodic.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 31 (1990), S. 901-915 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The relativistic evolution of a system of particles in the proper-time Schwinger–DeWitt formalism is investigated. For a class of interactions that can be represented as Fourier transforms of bounded complex matrix-valued measures, a Dyson series representation of the propagator is obtained. This class of interactions is non-Abelian and includes both external electromagnetic and Yang–Mills fields. The study of the relativistic problem is facilitated by embedding the original quantum evolution into a larger class of evolution problems that result if one makes an analytic continuation of the metric tensor gμν. This continuation is chosen so that the extended propagator shares (for all signatures of gμν ) the Gaussian decay properties typical of heat kernels. Estimates of the nth-order Dyson iterate kernels are found that ensure the absolute convergence of the perturbation series. In this fashion a number of analytic and smoothness properties of the propagator are determined. In particular, it is demonstrated that the convergent Dyson series representation constructs a fundamental solution of the equations of motion.
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