28 research outputs found
Two-boson Correlations in Various One-dimensional Traps
A one-dimensional system of two trapped bosons which interact through a
contact potential is studied using the optimized configuration interaction
method. The rapid convergence of the method is demonstrated for trapping
potentials of convex and non-convex shapes. The energy spectra, as well as
natural orbitals and their occupation numbers are determined in function of the
inter-boson interaction strength. Entanglement characteristics are discussed in
dependence on the shape of the confining potential.Comment: 5 pages, 3 figure
The Fokker-Planck equation for bistable potential in the optimized expansion
The optimized expansion is used to formulate a systematic approximation
scheme to the probability distribution of a stochastic system. The first order
approximation for the one-dimensional system driven by noise in an anharmonic
potential is shown to agree well with the exact solution of the Fokker-Planck
equation. Even for a bistable system the whole period of evolution to
equilibrium is correctly described at various noise intensities.Comment: 12 pages, LATEX, 3 Postscript figures compressed an
Quasi-exact solutions for two interacting electrons in two-dimensional anisotropic dots
We present an analysis of the two-dimensional Schrodinger equation for two
electrons interacting via Coulombic force and confined in an anizotropic
harmonic potential. The separable case of wy = 2wx is studied particularly
carefully. The closed-form expressions for bound-state energies and the
corresponding eigenfunctions are found at some particular values of wx. For
highly-accurate determination of energy levels at other values of wx, we apply
an efficient scheme based on the Frobenius expansion.Comment: 11 pages, 4 figure
Comparative study of quantum anharmonic potentials
We perform a study of various anharmonic potentials using a recently
developed method. We calculate both the wave functions and the energy
eigenvalues for the ground and first excited states of the quartic, sextic and
octic potentials with high precision, comparing the results with other
techniques available in the literature.Comment: 13 pages, 8 figures and 2 tables; revtex
Perturbative Expansion around the Gaussian Effective Potential of the Fermion Field Theory
We have extended the perturbative expansion method around the Gaussian
effective action to the fermionic field theory, by taking the 2-dimensional
Gross-Neveu model as an example. We have computed both the zero temperature and
the finite temperature effective potentials of the Gross-Neveu model up to the
first perturbative correction terms, and have found that the critical
temperature, at which dynamically broken symmetry is restored, is significantly
improved for small value of the flavour number.Comment: 14pages, no figures, other comments Typographical errors are
corrected and new references are adde
Perturbative Expansion around the Gaussian Effective Action: The Background Field Method
We develop a systematic method of the perturbative expansion around the
Gaussian effective action based on the background field method. We show, by
applying the method to the quantum mechanical anharmonic oscillator problem,
that even the first non-trivial correction terms greatly improve the Gaussian
approximation.Comment: 16 pages, 3 eps figures, uses RevTeX and epsf. Errors in Table 1 are
corrected and new references are adde
Convergence of the Optimized Delta Expansion for the Connected Vacuum Amplitude: Zero Dimensions
Recent proofs of the convergence of the linear delta expansion in zero and in
one dimensions have been limited to the analogue of the vacuum generating
functional in field theory. In zero dimensions it was shown that with an
appropriate, -dependent, choice of an optimizing parameter \l, which is an
important feature of the method, the sequence of approximants tends to
with an error proportional to . In the present paper we
establish the convergence of the linear delta expansion for the connected
vacuum function . We show that with the same choice of \l the
corresponding sequence tends to with an error proportional to . The rate of convergence of the latter sequence is governed by
the positions of the zeros of .Comment: 20 pages, LaTeX, Imperial/TP/92-93/5
The optimized Rayleigh-Ritz scheme for determining the quantum-mechanical spectrum
The convergence of the Rayleigh-Ritz method with nonlinear parameters
optimized through minimization of the trace of the truncated matrix is
demonstrated by a comparison with analytically known eigenstates of various
quasi-solvable systems. We show that the basis of the harmonic oscillator
eigenfunctions with optimized frequency ? enables determination of boundstate
energies of one-dimensional oscillators to an arbitrary accuracy, even in the
case of highly anharmonic multi-well potentials. The same is true in the
spherically symmetric case of V (r) = {\omega}2r2 2 + {\lambda}rk, if k > 0.
For spiked oscillators with k < -1, the basis of the pseudoharmonic oscillator
eigenfunctions with two parameters ? and {\gamma} is more suitable, and
optimization of the latter appears crucial for a precise determination of the
spectrum.Comment: 22 pages,8 figure
A Nonperturbative Study of Inverse Symmetry Breaking at High Temperatures
The optimized linear -expansion is applied to multi-field scalar theories at high temperatures. Using the imaginary time
formalism the thermal masses are evaluated perturbatively up to order
which considers consistently all two-loop contributions. A
variational procedure associated with the method generates nonperturbative
results which are used to search for parameters values for inverse symmetry
breaking (or symmetry nonrestoration) at high temperatures. Our results are
compared with the ones obtained by the one-loop perturbative approximation, the
gap equation solutions and the renormalization group approach, showing good
agreement with the latter method. Apart from strongly supporting inverse
symmetry breaking (or symmetry nonrestoration), our results reveal the
possibility of other high temperature symmetry breaking patterns for which the
last term in the breaking sequence is .Comment: 28 pages,5 eps figures (uses epsf), RevTeX. Only a small misprint in
Eq. (2.10) and a couple of typos fixe
Chiral and Gluon Condensates at Finite Temperature
We investigate the thermal behaviour of gluon and chiral condensates within
an effective Lagrangian of pseudoscalar mesons coupled to a scalar glueball.
This Lagrangian mimics the scale and chiral symmetries of QCD. (Submitted to Z.
Phys. C)Comment: 20 pages + 7 figures (uuencoded compressed postscript files),
University of Regensburg preprint TPR-94-1