Transformations In Phase Space Research Articles

Phase space transformation used at the FRM II backscattering spectrometer: concepts and technical realization

The technical aspects of the backscattering spectrometer for the FRM II reactor are discussed. Using a phase space transformation chopper the neutron flux at the backscattering energy will be enhanced without impairing the energy resolution of the instrument. Concepts and technical realizations are presented.

Design and optimisation of a backscattering spectrometer using a phase space transformation and super mirror guides

The use of a phase space transformation chopper for a new backscattering spectrometer, planned for the FRM I1 reactor in Munich, is discussed. It will be shown that a phase space transformation increases the neutron flux at the desired backscattering

Lie symmetries and conserved quantities of nonconservative nonholonomic systems in phase space

The invariance and conserved quantities of the nonconservative nonholonomic systems are studied by introducing the infinitesimal transformations in phase space. The Lie’s symmetrical determining equations are established. The Lie’s symmetrical structure equation is obtained. An example to illustrate the application of the result is given.

Phase Space Transformations of Gaussian Diffusions

It is shown that for Gaussian diffusions, the transformation back to Brownian motion, usually accomplished via the Girsanov (or Feynman–Kac) formula and time-shift, can be obtained by a classical canonical, i.e. symplectic, transformation in phase space. The method is based on constants of motion, in this case the Wronskian. Similar transformations for general diffusions are briefly discussed.

Linear canonical transformations and quantum phase: a unified canonical and algebraic approach

The algebra of generalized linear quantum canonical transformations is examined in the prespective of Schwinger's unitary-canonical basis. Formulation of the quantum phase problem within the theory of quantum canonical transformations and in particular with the generalized quantum action-angle phase space formalism is established and it is shown that the conceptual foundation of the quantum phase problem lies within the algebraic properties of the quantum canonical transformations in the quantum phase space. The representations of the Wigner function in the generalized action-angle unitary operator pair for certain Hamiltonian systems with the dynamical symmetry are examined. This generalized canonical formalism is applied to the quantum harmonic oscillator to examine the properties of the unitary quantum phase operator as well as the action-angle Wigner function.

Phase-Space Quantization of Field Theory

In this lecture, a limited introduction of gauge invariance in phase-space is provided, predicated on canonical transformations in quantum phase-space. Exact characteristic trajectories are also specified for the time-propagating Wigner phase-space distribution function: they are especially simple--indeed, classical--for the quantized simple harmonic oscillator. This serves as the underpinning of the field theoretic Wigner functional formulation introduced. Scalar field theory is thus reformulated in terms of distributions in field phase-space. This is a pedagogical selection from work published and reported at the Yukawa Institute Workshop ''Gauge Theory and Integrable Models'', 26-29 January, 1999.

Efficient Symplectic Integration of Satellite Orbits

The use of the extended phase space and time transformations for constructing efficient symplectic methods for computing the long term behavior of perturbed two‐body systems are discussed. Main applications are for artificial satellite orbits. The methods suggested here are efficient also for large eccentricities.

Canonical Symmetries in the Functional Formalism

Based on the phase-space generating functionalof the Green function, the canonical Ward identities(CWI) under local, nonlocal, and global transformationsin phase space for a system with a regular and singular Lagrangian have been derived. Therelation of global canonical symmetries to conservationlaws at the quantum level is presented. The advantage ofthis formulation is that one does not need to carry out the integration over canonicalmomenta in a phase-space path (functional) integral asin the traditional treatment in configuration space. Ingeneral, the connection between global canonicalsymmetries and conservation laws in classical theories isno longer preserved in quantum theories. Applications ofour formulation to the non-Abelian Chern-Simons (CS)theory are given, and new forms for CS gauge-ghost field proper vertices and the quantal conservedangular momentum of this system are obtained; thisangular momentum differs from the classical one in thatone needs to take into account the contribution of angular momenta of ghost fields.

Branching rules for restriction of the Weil representations of Sp(n,R) to its maximal parabolic subgroup CM(n)

The symplectic group Sp(n,R) is the group of linear canonical transformations of a real 2n-dimensional phase space and CM(n)⊂Sp(n,R) is a maximal parabolic subgroup. The symplectic groups are the fundamental dynamical groups of classical and quantal Hamiltonian mechanics. In particular, Sp(3,R) is the dynamical group of the spherical harmonic oscillator and its Weil (harmonic series) representations are important for the microscopic (shell model) description of the collective motions of many-particle systems. The subgroup CM(3)⊂Sp(3,R) also appears in the microscopic theory of nuclear collective motion as the dynamical group of a hydrodynamic model of quadrupole vibrations and rotations of a nucleus. Thus, the Sp(3,R)→CM(3) branching rules are needed in finding the embedding of the hydrodynamic collective model in the microscopic shell model. Some new developments are made in the vector-coherent-state theory of induced representations.

Twist phase in Gaussian-beam optics

The recently discovered twist phase is studied in the context of the full ten-parameter family of partially coherent general anisotropic Gaussian Schell-model beams. It is shown that the nonnegativity requirement on the cross-spectral density of the beam demands that the strength of the twist phase be bounded from above by the inverse of the transverse coherence area of the beam. The twist phase as a two-point function is shown to have the structure of the generalized Huygens kernel or Green's function of a first-order system. The ray-transfer matrix of this system is exhibited. Wolf-type coherent-mode decomposition of the twist phase is carried out. Imposition of the twist phase on an otherwise untwisted beam is shown to result in a linear transformation in the ray phase space of the Wigner distribution. Though this transformation preserves the four-dimensional phase-space volume, it is not symplectic and hence it can, when impressed on a Wigner distribution, push it out of the convex set of all bona fide Wigner distributions unless the original Wigner distribution was sufficiently deep into the interior of the set.

Noncanonical Hamiltonian methods for particle motion in magnetospheric hydromagnetic waves

Hamiltonian equations of motion for a nonrelativistic charged particle in magnetospheric hydromagnetic perturbations are derived. The equations are gyroaveraged, allowing much larger time steps in numerical solutions of the equations of motion compared to integrating the full Lorentz equations of motion, but they contain finite‐gyroradius effects to all orders in k⊥ρ, where k⊥. is the perpendicular wave number and ρ is the particle gyroradius. The finite‐gyroradius effects are essential for the important class of particles which undergo magnetic drift‐bounce resonances with the waves. The equations are derived by finding a Lie transform of the perturbed guiding center phase‐space Lagrangian to a new Lagrangian which is independent of the gyrophase angle. The resulting Euler‐Lagrange equations contain nonlinear terms which automatically preserve the Hamiltonian properties of the original Lorentz system, such as conservation of energy (for static systems) and conservation of phase‐space volume. The Hamiltonian conservation properties are useful for checking the accuracy of numerical integration schemes and they are essential for the use of Poincaré surface‐of‐section plots. Compared to more traditional canonical Hamiltonian methods, the phase‐space Lagrangian Lie transform methods allow general, noncanonical phase‐space coordinates and transformations. This results in more power and flexibility in finding convenient forms for the final equations of motion. The results are given in coordinate‐free form and in terms of magnetic field coordinates. Applications of these results to calculations of hydromagnetic wave‐induced particle motion in the inner magnetosphere are discussed.

Phase-space prediction of chaotic time series

We report on improved phase-space prediction of chaotic time series. We propose a new neighbour-searching strategy which corrects phase-space distortion arising from noise, finite sampling time and limited data length. We further establish a robust fitting algorithm which combines phase-space transformation, weighted regression and singular value decomposition least squares to construct a local linear prediction function. The scaling laws of prediction error in the presence of noise with various parameters are discussed. The method provides a practical iterated prediction approach with relatively high prediction performance. The prediction algorithm is tested on maps (Logistic, Hénon and Ikeda), finite flows (Rössler and Lorenz) and a laser experimental time series, and is shown to give a prediction time up to or longer than five times the Lyapunov time. The improved algorithm also gives a reliable prediction when using only a short training set and in the presence of small noise.

Canonical global symmetry in the functional integral formalism of the system and conservation laws

Based on the phase-space path integral (functional integral) for a system with a regular or singular Lagrangian, the generalized Ward identities for phase space generating functional under the global transformation in phase space are derived respectively. The canonical Noether theorem at the quantum level is also established. It is pointed out that the connection between the symmetries and conservation laws in classical theories, in general,is no longer preserved in quantum theories. The advantage of our formulation is that we do not need to carry out the integration over the canonical momenta as usually performed. Applying the present formulation to Yang-Mills theory, the quantal BRS conserved quantity and Ward-Takahashi identity for BRS tranformation are derived; the Ward identities for gaugeghost proper vertices and new quantal conserved quantity are also found. In comparison of quantal conservation laws with those one deriving from configuration-space path integral using the Faddeev-Popov(F-P) trick is discussed. A precise study of path-integral quantisation for a nonlinear sigma model with Hopf and Chern-Simons (CS) terms is reexamined. It has been shown that the angular momentum at the quantum level is equal to classical (Noether ) one. Applying our formulation to non-Abelian CS theory, the quantal conserved angular momentum of this system is obtained which differs from classical one in that one needs to take into account the contribution of angular momenta of ghost fields.

Canonical transformations to warped surfaces: Correction of aberrated optical images

The projection of optical images on warped screens is a canonical transformation of phase space between flat and warped evolution-parameter surfaces. In mechanics, the evolution parameter is time; in geometric optics it is the optical axis of coordinate space. We consider the specific problem of bringing to focus an axis-symmetric aberrating optical system by warping the output screen. The solution for the surface curvature coefficients is given in terms of the Lie aberration coefficients of the system; a linear optimization strategy applies.

A characterization of the Ligon-Schaaf regularization map

First, we give an explicit description of all the mappings from the phace space of the Kepler problem to the phase space of the geodesics on the sphere, which transform the constants of motion of the Kepler problem to the angular momentum. Second, among these we describe those mappings which in addition send Kepler solutions to parametrized geodesics. Third, we describe those mappings which in addition are canonical transformations of the respective phase space. Finally we prove that among these the Ligon-Schaaf map is the unique one which maps the collison orbits to the geodesics which pass through the north pole. In this way we also give a new proof that the Ligon-Schaaf map has all the properties described above.

Factorization of complex canonical transformations

We investigate the Lie series representation of the canonical transformations in a finite dimensional complex phase space. It is shown that any transformation of this type can be factorized into a product of three factors associated with a pure imaginary generating function, a holomorphic function, and an element of the cyclic group C4. The imaginary function can be considered as an observable in the sense of classical mechanics. Some hints are given which suggest that the holomorphic function can be connected with the notion of the state of a physical system. Moreover, a special kind of mappings is studied which provides a link between entropy, action, and state functions. The occurrence of these important physical quantities shows that the mathematical structure goes beyond a formal analogy to quantum physics at least in the finite dimensional case.

Canonical Quantal Symmetry and Conserved Charges for a System with Higher-Order Lagrangian11The project supported by National Natural Science Foundation of China under grant 19275009

Based on the phase space generating functional of Green function for a system with regular higher-order Lagrangian, the conserved charge is deduced at quantum level if the canonical action is invariant under the global symmetry transformation in extended phase space. The generalization of our results to a system with singular higher-order Lagrangian is also studied. In general the quantal conserved charges are different from classical ones.

Canonical global symmetry and quantal conservation laws for a system with singular higher order Lagrangian

Starting from the phase-space generating functional of the Green function for a system with singular higher order Lagrangian, the generalized canonical Ward identities under the global symmetry transformation in phase space is deduced. The local transformation connected with this global symmetry transformation is studied, and the quantal conservation laws are obtained for such a system. We give a preliminary application to higher derivative Yang-Mills theory; a generalized quantal BRS conserved quantity is found.

Perturbed Gylden Systems and Time-Dependent Delaunay-Like Transformations

We study the possibilities and limitations of the application of generalized Delaunay-like transformations (in the 6-dimensional phase space) and TR-like mappings (in the 8-dimensional, extended phase space) to perturbed two-body problems with a time-varying Keplerian parameter μ(t), that is, to Gylden-type systems. For the sake of theoretical completeness, both negative- and positive-energy motion (with nonstation-ary coupling parameter) are, in principle, considered. Our developments are intended to introduce canonical variables parallelling the classical ones of Delaunay and the Delaunay-Similar variables of Scheifele.

Practical Symplectic Methods with Time Transformation for the Few-Body Problem

The use of the extended phase space and time transformations for constructing efficient symplectic algorithms for the investigation of long term behavior of hierarchical few-body systems is discussed. Numerical experiments suggest that the time-transformed generalized leap-frog, combined with symplectic correctors, is one of the most efficient methods for such studies. Applications extend from perturbed two-body motion to hierarchical many-body systems with large eccentricities.