Faddeev-Merkuriev equations for resonances in three-body Coulombic systems

We reconsider the homogeneous Faddeev-Merkuriev integral equations for three-body Coulombic systems with attractive Coulomb interactions and point out that the resonant solutions are contaminated with spurious resonances. The spurious solutions are related to the splitting of the attractive Coulomb potential into short- and long-range parts, which is inherent in the approach, but arbitrary to some extent. By varying the parameters of the splitting the spurious solutions can easily be ruled out. We solve the integral equations by using the Coulomb-Sturmian separable expansion approach. This solution method provides an exact description of the threshold phenomena. We have found several new S-wave resonances in the e- e+ e- system in the vicinity of thresholds.Comment: LaTeX with elsart.sty 13 pages, 5 figure

Augmin-dependent microtubule nucleation at microtubule walls in the spindle

© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Cell Biology 202 (2013): 25-33, doi:10.1083/jcb.201304031.The formation of a functional spindle requires microtubule (MT) nucleation from within the spindle, which depends on augmin. How augmin contributes to MT formation and organization is not known because augmin-dependent MTs have never been specifically visualized. In this paper, we identify augmin-dependent MTs and their connections to other MTs by electron tomography and 3D modeling. In metaphase spindles of human cells, the minus ends of MTs were located both around the centriole and in the body of the spindle. When augmin was knocked down, the latter population of MTs was significantly reduced. In control cells, we identified connections between the wall of one MT and the minus end of a neighboring MT. Interestingly, the connected MTs were nearly parallel, unlike other examples of end–wall connections between cytoskeletal polymers. Our observations support the concept of augmin-dependent MT nucleation at the walls of existing spindle MTs. Furthermore, they suggest a mechanism for maintaining polarized MT organization, even when noncentrosomal MT initiation is widespread.This work was supported by the Next Generation grant (Japan Society for the Promotion of Science), Human Frontier Science Program, James A. and Faith Miller Memorial Fund (to G. Goshima), the Hori Sciences and Arts Foundation, the Sasakawa Scientific Research Grant, the Kazato Research foundation (to T. Kamasaki), and the National Institutes of Health (8P41GM103431-42 to A. Hoenger). T. Kamasaki was a recipient of the Japan Society for the Promotion of Science postdoctoral fellowship.2014-01-0

Absorption spectrum of a weakly n-doped semiconductor quantum well

We calculate, as a function of temperature and conduction band electron density, the optical absorption of a weakly n-doped, idealized semiconductor quantum well. In particular, we focus on the absorption band due to the formation of a charged exciton. We conceptualize the charged exciton as an itinerant excitation intimately linked to the dynamical response of itinerant conduction band electrons to the appearance of the photo-generated valence band hole. Numerical results for the absorption in the vicinity of the exciton line are presented and the spectral weights associated with, respectively, the charged exciton band and the exciton line are analyzed in detail. We find, in qualitative agreement with experimental data, that the spectral weight of the charged exciton grows with increasing conduction band electron density and/or decreasing temperature at the expense of the exciton.Comment: 5 pages, 4 figure

New representation of orbital motion with arbitrary angular momenta

A new formulation is presented for a variational calculation of $N$-body systems on a correlated Gaussian basis with arbitrary angular momenta. The rotational motion of the system is described with a single spherical harmonic of the total angular momentum $L$, and thereby needs no explicit coupling of partial waves between particles. A simple generating function for the correlated Gaussian is exploited to derive the matrix elements. The formulation is applied to various Coulomb three-body systems such as $e^-e^-e^+, tt\mu, td\mu$, and $\alpha e^-e^-$ up to $L=4$ in order to show its usefulness and versatility. A stochastic selection of the basis functions gives good results for various angular momentum states.Comment: Revte

Second bound state of the positronium molecule and biexcitons

A new, hitherto unknown bound state of the positronium molecule, with orbital angular momentum L=1 and negative parity is reported. This state is stable against autodissociation even if the masses of the positive and negative charges are not equal. The existence of a similar state in two-dimension has also been investigated. The fact that the biexcitons have a second bound state may help the better understanding of their binding mechanism.Comment: Latex, 8 pages, 2 Postscript figure

Analytic Evaluation of Four-Particle Integrals with Complex Parameters

The method for analytic evaluation of four-particle integrals, proposed by Fromm and Hill, is generalized to include complex exponential parameters. An original procedure of numerical branch tracking for multiple valued functions is developed. It allows high precision variational solution of the Coulomb four-body problem in a basis of exponential-trigonometric functions of interparticle separations. Numerical results demonstrate high efficiency and versatility of the new method.Comment: 13 pages, 4 figure

Four-Body Bound State Calculations in Three-Dimensional Approach

The four-body bound state with two-body interactions is formulated in Three-Dimensional approach, a recently developed momentum space representation which greatly simplifies the numerical calculations of few-body systems without performing the partial wave decomposition. The obtained three-dimensional Faddeev-Yakubovsky integral equations are solved with two-body potentials. Results for four-body binding energies are in good agreement with achievements of the other methods.Comment: 29 pages, 2 eps figures, 8 tables, REVTeX

Benchmark Test Calculation of a Four-Nucleon Bound State

In the past, several efficient methods have been developed to solve the Schroedinger equation for four-nucleon bound states accurately. These are the Faddeev-Yakubovsky, the coupled-rearrangement-channel Gaussian-basis variational, the stochastic variational, the hyperspherical variational, the Green's function Monte Carlo, the no-core shell model and the effective interaction hyperspherical harmonic methods. In this article we compare the energy eigenvalue results and some wave function properties using the realistic AV8' NN interaction. The results of all schemes agree very well showing the high accuracy of our present ability to calculate the four-nucleon bound state.Comment: 17 pages, 1 figure

Global-Vector Representation of the Angular Motion of Few-Particle Systems II

The angular motion of a few-body system is described with global vectors which depend on the positions of the particles. The previous study using a single global vector is extended to make it possible to describe both natural and unnatural parity states. Numerical examples include three- and four-nucleon systems interacting via nucleon-nucleon potentials of AV8 type and a 3$\alpha$ system with a nonlocal $\alpha\alpha$ potential. The results using the explicitly correlated Gaussian basis with the global vectors are shown to be in good agreement with those of other methods. A unique role of the unnatural parity component, caused by the tensor force, is clarified in the $0^-_1$ state of $^4$He. Two-particle correlation function is calculated in the coordinate and momentum spaces to show different characteristics of the interactions employed.Comment: 39 pages, 4 figure