A Theoretical Solution for a Nonlinear Master Equation

Based on the master equation describing the interaction of a single-mode bosonic state with a heat bath at finite temperature in the Born-Markov approximation, we constructed a new nonlinear master equation and derived the infinite operator sum representation of quasi-Kraus operators for the density operator     

Nine-propagator master integrals for massless three-loop form factors

We complete the calculation of master integrals for massless three-loop form factors by computing the previously-unknown three diagrams with nine propagators in dimensional regularisation. Each of the integrals yields a six-fold Mellin–Barnes representation which we use to compute the coefficients of the Laurent expansion in ?. Using Riemann ζ functions of up to weight six, we give fully analytic results for one integral; for a second, analytic results for all but the finite term; for the third, analytic results for all but the last two coefficients in the Laurent expansion. The remaining coefficients are given numerically to sufficiently high accuracy for phenomenological applications.     

Ergodic theory and visualization. I. Mesochronic plots for visualization of ergodic partition and invariant sets

We present a computational study of a visualization method for invariant sets based on ergodic partition theory, first proposed by Mezic? (Ph.D. thesis, Caltech, 1994) and Mezic? and Wiggins [Chaos 9, 213 (1999)]. The algorithms for computation of the time averages of observables on phase space are developed and used to provide an approximation of the ergodic partition of the phase space. We term the graphical representation of this approximation--based on time averages of observables--a mesochronic plot (from Greek: meso--mean, chronos--time). The method is useful for identifying low-dimensional projections (e.g., two-dimensional slices) of invariant structures in phase spaces of dimensionality bigger than two. We also introduce the concept of the ergodic quotient space, obtained by assigning a point to every ergodic set, and provide an embedding method whose graphical representation we call the mesochronic scatter plot. We use the Chirikov standard map as a well-known and dynamically rich example in order to illustrate the implementation of our methods. In addition, we expose applications to other higher dimensional maps such as the Froe?schle map for which we utilize our methods to analyze merging of resonances and, the three-dimensional extended standard map for which we study the conjecture on its ergodicity [I. Mezic?, Physica D 154, 51 (2001)]. We extend the study in our next paper [Z. Levnajic? and I. Mezic?, e-print arXiv:0808.2182] by investigating the visualization of periodic sets using harmonic time averages. Both of these methods are related to eigenspace structure of the Koopman operator [I. Mezic? and A. Banaszuk, Physica D 197, 101 (2004)].     

Approximating moments of acoustic fields in random media

Abstract

Starting from a path integral representation of the fourth moment of an acoustic field, two types of approximations are considered in detail: a ‘zero-kink’ approximation and a ‘single-kink’ approximation. The expressions ‘zero-kink’ and ‘single-kink’ describe families of paths which are used to approximate path integrals over all continuous paths. The single-kink approximation reduces the propagation problem to a phase screen problem with fluctuations on the phase screen containing information about fluctuations along entire paths from source to receiver.     

Electronic structure and kinetic properties of tight-binding metals at high temperature

The influence of the electron-phonon interaction on the electronic properties of tight-binding metals is considered with the one-band approximation. It is shown by using the previous results that the existence of the twofold effect is due to phonons. Firstly, phonons lead to a non-coherent scattering of electrons and as a result a finite lifetime for the electron states. Secondly, phonons lead to a renormalization of the periodic cristal potential. Latter was well known for the nearly free-electron crystals to be expressed as Debye-Waller corrections to the lattice potential. Such effect in tight-binding metals is shown here to result in the temperature dependence of overlap integrals. It gives rise to the increase of the band width and the electron velocity for the one-band approximation. The negative temperature coefficient of resistivity is shown to may arise in result at high temperatures.     

Approximating moments of acoustic fields in random media

Starting from a path integral representation of the fourth moment of an acoustic field, two types of approximations are considered in detail: a 'zero-kink' approximation and a 'single-kink' approximation. The expressions 'zero-kink' and 'single-kink' describe families of paths which are used to approximate path integrals over all continuous paths. The single-kink approximation reduces the propagation problem to a phase screen problem with fluctuations on the phase screen containing information about fluctuations along entire paths from source to receiver.     

The Number of Master Integrals is Finite

For a fixed Feynman graph one can consider Feynman integrals with all possible powers of propagators and try to reduce them, by linear relations, to a finite subset of integrals, the so-called master integrals. Up to now, there are numerous examples of reduction procedures resulting in a finite number of master integrals for various families of Feynman integrals. However, up to now it was just an empirical fact that the reduction procedure results in a finite number of irreducible integrals. It this paper we prove that the number of master integrals is always finite.     

Approximation of the electron density of Aluminium clusters in tensor-product format

The tensor-structured methods developed recently for the accurate calculation of the Hartree and the non-local exchange operators have been applied successfully to the ab initio numerical solution of the Hartree–Fock equation for some molecules. In the present work, we show that the rank-structured representation can be gainfully applied to the accurate approximation of the electron density of large Aluminium clusters. We consider the Tucker-type decomposition of the electron density of certain Aluminium clusters originating from finite element calculations in the framework of the orbital-free density functional theory. Numerical investigations of the Tucker approximation of the corresponding electron density reveal the exponential decay of the approximation error with respect to the Tucker rank. The resulting low-rank tensor representation reduces dramatically the storage needs and the computational complexity of the consequent tensor operations on the electron density. As main result, the rank of the Tucker approximation for the accurate representation of the electron density is small and only weakly dependent on the system size for the systems studied here. This shows good promise for resolving the electronic structure of materials using tensor-structured techniques.     

Correlations of nearby levels induced by a random potential

We consider a Hamiltonian H which is the sum of a deterministic part H₀ and of a random potential V. For finite N x N matrices, following a method introduced by Kazakov, we derive a representation of the correlation functions in terms of contour integrals over a finite number of variables. This allows one to analyse the level correlations, whereas the standard methods of random matrix theory, such as the method of orthogonal polynomials, are not available for such cases. At short distance we recover, for an arbitrary H₀ an oscillating behavior for the connected two-level correlation.     

Uniform approximation for the coherent-state propagator using a conjugate application of the Bargmann representation

We propose a conjugate application of the Bargmann representation of quantum mechanics. Applying the Maslov method to the semiclassical connection formula between the two representations, we derive a uniform semiclassical approximation for the coherent-state propagator which is finite at phase space caustics.     

Spin-other-orbit interaction in highly excited configurations with p and g electrons in outer shells

The matrix of the operator of the spin-other-orbit interaction energy is constructed for npn’g and np ⁵ n’g configurations. The matrix elements of this operator are calculated in the single-configuration approximation with wave functions in the LSJM representation and in the representation of uncoupled angular momenta using the known general formulas. The spin-other-orbit interaction is represented by three direct and three exchange radial Marvin spin interaction integrals.     

Permutation approach to finite-alphabet stationary stochastic processes based on the duality between values and orderings

The duality between values and orderings is a powerful tool to discuss relationships between various information-theoretic measures and their permutation analogues for discrete-time finite-alphabet stationary stochastic processes (SSPs). Applying it to output processes of hidden Markov models with ergodic internal processes, we have shown in our previous work that the excess entropy and the transfer entropy rate coincide with their permutation analogues. In this paper, we discuss two permutation characterizations of the two measures for general ergodic SSPs not necessarily having the Markov property assumed in our previous work. In the first approach, we show that the excess entropy and the transfer entropy rate of an ergodic SSP can be obtained as the limits of permutation analogues of them for the N-th order approximation by hidden Markov models, respectively. In the second approach, we employ the modified permutation partition of the set of words which considers equalities of symbols in addition to permutations of words. We show that the excess entropy and the transfer entropy rate of an ergodic SSP are equal to their modified permutation analogues, respectively.     

An analogue model for KSV theory

An analogue model based upon the association of amplitudes for many particle processes with functional integrals over interaction regions of the exponential of the energy of momentum flow is shown to yield in first approximation the multiparticle Veneziano representation. The correction terms in the next approximation are shown to be just those given by the planar loop amplitude in the theory of Kikkawa, Sakita and Virasoro. This approach casts new light upon the divergence problem of the loop amplitudes in a dual theory but is does not provide, as yet, an unambiguous answer to it.     

Limit Theorems for Self-Similar Tilings

We study deviation of ergodic averages for dynamical systems given by self-similar tilings on the plane and in higher dimensions. The main object of our paper is a special family of finitely-additive measures for our systems. An asymptotic formula is given for ergodic integrals in terms of these finitely-additive measures, and, as a corollary, limit theorems are obtained for dynamical systems given by self-similar tilings.     

A path integral approach to asset-liability management

Functional integrals constitute a powerful tool in the investigation of financial models. In the recent econophysics literature, this technique was successfully used for the pricing of a number of derivative securities. In the present contribution, we introduce this approach to the field of asset-liability management. We work with a representation of cash flows by means of a two-dimensional delta-function perturbation, in the case of a Brownian model and a geometric Brownian model. We derive closed-form solutions for a finite horizon ALM policy. The results are numerically and graphically illustrated.     

Coherent states and path integrals for model hamiltonians in quantum optics

A brief review of applications of the coherent states (CSes) in quantum optics is given. The CS representation of path integrals in the semi-classical approximation leads to the classical dynamics of CS parameters. Calculations of squeezing in the model of spontaneous parametric scattering are performed and the chaos in the collective dynamics of three-level atoms interacting with resonant photon modes is studied.     

Slave bosons in radial gauge: A bridge between path integral and Hamiltonian language

We establish a correspondence between the resummation of world lines and the diagonalization of the Hamiltonian for a strongly correlated electronic system. For this purpose, we analyze the functional integrals for the partition function and the correlation functions invoking a slave boson representation in the radial gauge. We show in the spinless case that the Green's function of the physical electron and the projected Green's function of the pseudofermion coincide. Correlation and Green's functions in the spinful case involve a complex entanglement of the world lines which, however, can be obtained through a strikingly simple extension of the spinless scheme. As a toy model we investigate the two-site cluster of the single impurity Anderson model which yields analytical results. All expectation values and dynamical correlation functions are obtained from the exact calculation of the relevant functional integrals. The hole density, the hole auto-correlation function and the Green's function are computed, and a comparison between spinless and spin 1/2 systems provides insight into the role of the radial slave boson field. In particular, the exact expectation value of the radial slave boson field is finite in both cases, and it is not related to a Bose condensate.     

Propagation of a vectorial Laguerre–Gaussian beam beyond the paraxial approximation

Based on the vectorial Rayleigh–Sommerfeld integrals, the analytical propagation expression of a vectorial Laguerre–Gaussian beam beyond paraxial approximation is presented. The far field expression and the scalar paraxial result are obtained as special cases of the general formulae. According to the analytical representation, the light intensity distribution of the vectorial Laguerre–Gaussian beam is depicted in the reference plane. The light intensity distribution of a vectorial Laguerre–Gaussian beam with cos m is also compared with that of a vectorial Laguerre–Gaussian beam with sin m.