Features of quasiparticle decay in 2D electronic systems with spin–orbit interaction

The dependence of the width of the spectral function of electrons and holes on the wavevector and excitation energy in a 2D electron system with spin-orbit interaction caused by structural inversion asymmetry is analyzed in the G ⁰ W ⁰ approximation. It is shown that an additional (relative to the generation of electron-hole pairs) channel of hole decay due to emission of a plasmon appears in the case of low electron density. Noticeable spin asymmetry of the spectral function width appears in the region of electron excitations.     

Local-potential approximation for the Brueckner G matrix and problem of optimally choosing model subspace

The validity of the local-potential approximation, which was proposed previously for the singlet-pairing problem in semi-infinite nuclear matter, is investigated in the Bethe-Goldstone equation for the Brueckner G matrix. For this purpose, use is made of the method developed earlier for solving this equation for a planar slab of nuclear matter in the case of a separable form of NN interaction. The ¹ S ₀ singlet and the ³ S ₁+³ D ₁ triplet channel are considered. The complete two-particle Hilbert space is split into a model and the complementary subspace that are separated by an energy E ₀. The two-particle propagator is calculated precisely in the first subspace, and the local-potential approximation is used in the second subspace. With an eye to subsequently employing the G matrix to calculate the Landau-Migdal amplitude, the total two-particle energy is fixed at E=2μ, where μ is the chemical potential of the system under consideration. Specific numerical calculations are performed at μ=?8 MeV. The applicability of the local-potential approximation is investigated versus the cutoff energy E ₀. It is shown that, in either channel being considered, the accuracy of the local-potential approximation is rather high for E ₀≥10 MeV.     

Time-dependent mean field S-matrix theory

By using the path integral approach to many-body systems, we formulate a time-dependent mean field S-matrix theory of nuclear reactions. Many-body channel eigenstates are constructed by using projection techniques. In this way the S-matrix between the channel eigenstates is expressed as a superposition of S-matrix elements between wave-packet-like states localized in space and time. A field operator representation of the interaction picture S-matrix is derived which enables one to apply the path integral approach. Applying the stationary phase approximation to the path integral representation of the interaction picture S-matrix between the localized states an asymptotically constant time-dependent mean field approximation to this S-matrix is obtained. Finally, the S-matrix between the projected channel eigenstates is obtained by evaluating the integral, arising from the projections, over the space-time positions of the localized states in the stationary phase approximation. The stationary phase conditions select those localized states from the projected channel states for which the mean field values of energy and momentum coincide with their corresponding channel eigenvalues.     

Padé approximation methods applied to the intermolecular force series

The H(1s)-H⁺, He-He, H(1s)-H(1s) and H(1s)-H(2s) interactions are considered as model systems for investigating the use of the Padé approximation method in summing the R ^-1 intermolecular force series. Various Padé approximants and partial sums of the R ^-1 expansions of the second-order Coulomb interaction energies are compared with the corresponding non-expanded results for each interaction. The computations are based on Unsöld's average energy approximation and on exact results for the H(1s)-H interaction. The results indicate that the Padé approximation method is a simple, useful way to remove some of the difficulties associated with the slow rate of convergence of the R ^-1 force series but that it does not alleviate the problems associated with the asymptotic divergent nature of the series. The results for the H(1s)-H⁺ interaction illustrate a possible difficulty in using Unsöld's method in the calculation of interaction energies.     

Many-body corrections to the nuclear anapole moment

The many body contributions to the nuclear anapole moment of ¹³³Cs, ²⁰⁵TI, ^207,209Pb and ²⁰⁹Bi are calculated in the random-phase approximation with the effective residual interaction. A strong reduction of a valence nucleon contribution was found, caused by the core polarization effects. The new type of contribution to the anapole moment from the core particles due to the induced weak interaction was calculated. The last contribution compensates the former reduction to large extent. The compensation is complete in the leading approximation if the proton-neutron residual forces are absent.     

Coupled channel approach to subbarrier fusion cross section

We present a reduced coupled channel method to treat a large number of coupled equations. This method is shown to be a good approximation to the exact coupled channel method for the fusion calculation even in the system involving strong coupling to high spin states. This method is applied to the analysis of subbarrier fusion cross sections for^148,150,154Sm+¹⁶O,²³²Th+¹⁶O and²³⁶U +¹²C. We show that the channel coupling to low-lying collective states can explain the magnitude of the fusion cross sections, whereas it underestimates the measured mean square values of spin distribution for²³²Th+¹⁶O and²³⁶U+¹²C. This discrepancy is discussed from the viewpoint of the WKB model.     

Langevin approach for stochastic Hodgkin–Huxley dynamics with discretization of channel open fraction

The random opening and closing of ion channels establishes channel noise, which can be approximated and included into stochastic differential equations (Langevin approach). The Langevin approach is often incorporated to model stochastic ion channel dynamics for systems with a large number of channels. Here, we introduce a discretization procedure of a channel-based Langevin approach to simulate the stochastic channel dynamics with small and intermediate numbers of channels. We show that our Langevin approach with discrete channel open fractions can give a good approximation of the original Markov dynamics even for only 10 K⁺$10{\text{K}}^{+}$ channels. We suggest that the better approximation by the discretized Langevin approach originates from the improved representation of events that trigger action potentials.     

Cross sections and asymmetries for elastic π3He scattering in the energy region around the Δ resonance

For a polarized target, π³He interaction is studied in the fixed-center approximation with all rescatterings included. Only the P ₃₃ wave is taken for the πN interaction. The nuclear wave function is taken either as a sum of Gaussian functions or as a Faddeev wave function in the s-wave approximation. The differential cross sections and asymmetries for elastic π⁺³He scattering at the laboratory energies of T _π, 180, and 256 MeV are calculated. The results are compared with experimental data.     

New BCS and renormalized QRPA formalism with application to double beta decay

A new analysis of the renormalized proton–neutron quasiparticle random phase approximation based on simultaneous recalculation of the one-body density matrix and the pairing tensor has been used to study the double beta decay. We demonstrated that inclusion of the quasiparticle correlations at the BCS level reduces ground state correlations in the particle–particle channel of the proton–neutron interaction. We also simplified the RQRPA equations significantly obtaining a low-dimensioned set of linear equations for the quasiparticle densities. The formalism was applied to the double beta decay of ⁷⁶Ge. Received: 4 January 1999 / Revised version: 29 March 1999     

Reaction cross sections for collisions involving exotic light nuclei within the glauber approach

The reaction cross sections for the interaction of exotic nuclei ⁶He and ¹¹Li with ¹²C nuclei are calculated for energies of about 0.8 GeV per nucleon. The cross sections calculated by the exact Glauber formula are compared with their counterparts found by using the formulas of the optical limit, the rigidtarget approximation, and the few-body approximation. The effect of the structure of the nuclei being considered on the calculated cross sections is examined. The root-mean-square radii of the ⁶He and ¹¹Li nuclei are estimated on the basis of experimental data on the cross sections for the interaction of these exotic nuclei with ¹²C nuclei.     

Effect of hyperon channels in low-energyK − d scattering

Within the framework of a Faddeev formalism and an implicit hyperon channel approximation, we have calculatedK ^? d elastic, total, and reaction cross sections for incident kaon laboratory momenta up to 120 Mev/c. We have used as input two different (slightly modified) multichannelM matrix fits to low-energy¯KN scattering, each of which contains explicitly theπ Y channels, as well as a single channel representation of the¯KN interaction in which the hyperon channels appear only through their contributions to the imaginary parts of the¯KN scattering lengths. TheK ^? d cross sections obtained with the single channel¯KN input differ by only some 10% from those for which we used the multichannel¯KN input. TheK ^? d cross sections calculated using¯KN input parameters from each of the two separateM matrix fits differ across the entire momentum range investigated by 25–35%.     

Energy levels of 1s~2n d(n≤9)states for lithium-like ions

The full-core plus correlation method with multi-configuration interaction wave functions is extended to the calculation of the non-relativistic energies of 1s²nd (n ≤ 9) states for the lithium isoelectronic sequence from Z = 11 to 20. Relativistic and mass-polarization effects on the energy are calculated as the first-order perturbation correction. The quantum-electrodynamics correction is also included. The fine structure splittings are determined from the expectation values of spin—orbit and spin—other-orbit interaction operators in the Pauli—Breit approximation. Combining the term energies of lowly excited states obtained with the quantum defects calculated by the single channel quantum defect theory, each of which is a smooth function of energy and approximated by a weakly varying function of energy, the ion potentials of highly excited states (n ≤ 6) are obtained with the semi-empirical iteration method. The results are compared with experimental data in the literature and found to be closely consistent with the regularity.     

An asymptotic normalization coefficient for the loosely-bounded state of 17F nucleus in the orthogonality conditions model

A method for calculating an asymptotic normalization coefficient (ANC) is developed within an approximation of the resonating group model (RGM)-the orthogonality conditions model (OCM). An ANC for the ¹⁶O + p channel of the (1/2⁺, 495.3 keV) state of the ¹⁷F nucleus is calculated using different versions of the model. It is shown that the influence of the exchange terms on the values of the ANC is quite great and is not reduced to renormalizing the channel wave function as a whole.     

Deconstructing <Superscript>1</Superscript>S<Subscript>0</Subscript> nucleon-nucleon scattering

A distorted-wave method is used to analyse nucleon-nucleon scattering in the ¹ S ₀ channel. Effects of one-pion exchange are removed from the empirical phase shift to all orders by using a modified effective-range expansion. Two-pion exchange is then subtracted in the distorted-wave Born approximation, with matrix elements taken between scattering waves for the one-pion exchange potential. The residual short-range interaction shows a very rapid energy dependence for kinetic energies above about 100MeV, suggesting that the breakdown scale of the corresponding effective theory is only 270MeV. This may signal the need to include the D \Delta -resonance as an explicit degree of freedom in order to describe scattering at these energies. An alternative strategy of keeping the cutoff finite to reduce large, but finite, contributions from the long-range forces is also discussed.     

Effect of residual interactions on nuclear level densities

We calculate the contribution of residual interactions to nuclear level densities in the framework of the random-phase approximation. We first investigate the case of the schematic model for which analytical formulae can be worked out. More realistic calculations are performed numerically for ⁴⁰Ca and ⁵⁶Ni using oscillator wave functions and a zero-range interaction. In ⁵⁶Ni it is found that residual interactions increase level densities significantly in the random-phase approximation, while small corrections are found in ⁴⁰Ca. A comparison with the results of second-order perturbation theory is presented.     

类钠铜离子的激发自电离

在扭曲波库仑玻恩交换近似下计算了类钠铜离子２ｐ^６３ｓ＋ｅ^-→２ｐ⁵３ｓ３ｌ＋ｅ^-（ｌ＝０，１，２）的内壳层激发截面．结合单组态近似和组态相互作用两种情况下计算的自电离分支比，计算了上述组态的激发自电离截面．结果表明，在入射电子能量为１０９０ｅＶ时，组态相互作用使２ｐ⁵３ｓ３ｄ总的激发自电离截面增大至单组态近似的近两倍；而使２ｐ⁵３ｓ²组态的激发自电离截面减小为单组态近似的３６％；２ｐ⁵３ｓ３ｐ组态的激发自电离截面只是略有下降 关键词：     

Stoßausrichtung in Molekularstrahlen

Collision alignment has been found in a beam of thermal Gallium atoms of² P _3/2-state emerging from an oven through a channel being wide compared with mean free path inside the oven and narrow compared with that one outside. Alignment effect is ascribed to “loss impacts” in the channel and the difference in scattering cross section for states of different orientation having been the subject of a previous paper. Calculation of the effect in linear approximation is discussed together with experimental data.     

The role of iterative isobar processes in nuclear matter and the effective nucleon-nucleon interaction

A calculation is performed using lowest order Brueckner theory in momentum space, with explicit isobar configurations included through the coupled channel mathod. The effective interaction for the¹ S ₀-⁵ D ₀ channel is extracted from this calculation. Two different transition potentials are used — one due to Green and Niskanen (1976), the other, due to Green and co-workers (1978). The nucleon-nucleon (NN) interaction used is the Reid soft core potential, compensated for the inclusion of the explicit isobar channel. The effective interaction shows marked momentum dependence in the intermediate range. The loss of attraction depends on the transition potential one chooses. The correlation function involving the nucleon-isobar intermediate state is anti-correlated to the NN part.