Electromagnetic form factors for nucleons and pions at positive and negative q 2 in the model of quark-gluon strings

The electromagnetic form factors for pions and nucleons are considered within the model of quark-gluon strings, where the momentum-transfer dependence of hadronic form factors is determined by the intercepts of the corresponding Regge trajectories and by the Sudakov form factor. Analytic expressions found for form factors in the timelike region admit an analytic continuation to the spacelike region. The resulting form factors for pions and nucleons comply well with experimental data both for positive and for negative values of the squared momentum transfer q ². It is shown that the distinctions between the absolute values of the pion and nucleon form factors F _π(q ²), G _m (q ²), and F ₂(q ²) at positive values of q ² and those at negative values of this variable are associated with the analytic properties of the double-logarithmic term in the exponent of the Sudakov form factor. The spin structure of the amplitudes for quark transitions into hadrons that is proposed in the present study makes it possible to describe fairly well available experimental data on the Pauli form factor F ₂ and on the ratio G _e /G _m .     

Semiclassical method for calculating the energetic values of helium, lithium and beryllium atoms

In previous papers we have presented a wave model for conservative bound systems resulted from the equivalency between the Schrödinger and wave equations. We proved that the normal curves of the characteristic surface of the wave equation, denoted by C curves, are solutions of the Hamilton-Jacobi equation, written for the same system, and correspond to the same constants of motion as those resulting from the Schrödinger equation. In this paper we present a method for computing the energetic values of conservative bound systems which is based on the properties of the C curves. The method is applied to the 1s ² state of helium, 1s ²2s and 1s ²2p states of lithium and 1s ²2s ² state of beryllium. Our theoretical values are compared with experimental data taken from well-known books. The relative error of our method is less than 5 x 10^?3.     

The 4d auger,coster-kronig,and recombination spectra of the lanthanides

A complete set of electron-excited 4d-basedAuger spectra of the lanthanide metals from lanthanum to lutetium (except the unstable promethium) is presented, in both differential and integral forms. It is believed that the set is more representative of clean surfaces of the lanthanides than any published hitherto. With the help of binding energy and electron loss measurements made in this laboratory and elsewhere, values of the various possible Auger, Coster—Kronig, and direct recombination transition energies are calculated, and for each transition a “centre of gravity” is derived based on relative intensities of final state multiplets, electron occupation of core levels, etc. By using arguments based on trends in the spectra across the series, on theoretically and experimentally derived values of U_eff for the difference 4fⁿ⁺¹→4f^n?1, and on plausibility, values of U_eff for 4fⁿ→ 4f^n?2 as well as for the other final state hole pair configurations are allocated. The relaxed transition energies so calculated are then compared with the experimental energies, from which it is possible in most cases to make assignment of the spectral features to the various transitions. As a result it is found that there are some significant disagreements with the theoretical rates of McGuire for lanthanide free atoms. The reasons for these disagreements are discussed, and an empirical model based on effective 4f and 5d populations and on the restrictions imposed by spin alignment is used to resolve the differences qualitatively.     

Prediction of the compressibility of mixed alkali halides

A model has been recently proposed by Varotsos and Alexopoulos which permits the calculation of the compressibility k^d of the volume of a defect from elastic properties of the surrounding lattice. This expression for k^d in conjunction with the Born model, as modified by Smith and coworkers, permits the determination of the compressibility and its pressure dependence of an alkali halide mixed crystal. The application of the proposed method to the system KCl-KBr shows excellent agreement between the predicted and the experimental values obtained by Slagle and McKinstry and recently by Cain.     

The low-energy level structure and the electromagnetic properties of191Ir and193Ir

TheM 1 andE 2 reduced transition probabilities in¹⁹¹Ir and¹⁹⁹Ir have been calculated on the weak particle-core coupling model. The static moments of the ground state and the first three low-lying excited states have been computed. The theoretical values are in good agreement with the experimental results, in particular, the existing discrepancy between the theoretical and the experimental value for the magnetic moment of the first excited 5/2⁺ state, in both these nuclei, has been removed. The predicted sign of the quadrupole moment of the 2⁺ state in the neighbouring even-even nuclei is consistent with the results reported for Platinum nuclei. The level structure of both these nuclei has been calculated assuming the particle-core interaction to be dipole-dipole and quadrupole-quadrupole type.     

Nuclear asymptotic normalization coefficients for <Superscript>14</Superscript>N → <Superscript>13</Superscript>C + <Emphasis Type="Italic">p</Emphasis> configurations and astrophysical <Emphasis Type="Italic">S</Emphasis> factor for radiative proton capture

Empirical values of the asymptotic normalization coefficient for proton bound states in the ¹⁴N nucleus for the first five levels were obtained from an analysis of the experimental differential cross sections known from our measurements and from the literature for the reaction ¹³C(³He, d)¹⁴N in the projectile-energy range between about 15 and 40 MeV. The values obtained in this way were used to calculate the astrophysical S factors for the reaction ¹³C(p, γ)¹⁴N in the case of the population of the first five levels of the 14N nucleus. The calculations were based on the R-matrix approach. The calculated values are in good agreement with the experimental astrophysical S factor at energies below 1 MeV.     

Radiative and interelectronic-interaction corrections to the hyperfine splitting in highly charged B-like ions

The ground-state hyperfine splitting values of high-Z boronlike ions are calculated. Calculation of the interelectronic-interaction contribution is based on a combination of the 1/Z perturbation theory and the large-scale configuration-interaction Dirac-Fock-Sturm method. The screened QED corrections are evaluated utilizing an effective screening potential approach. Total hyperfine splitting energies are presented for several B-like ions of particular interest: ⁴⁵Sc¹⁶⁺, ⁵⁷Fe²¹⁺, ²⁰⁷Pb⁷⁷⁺, and ²⁰⁹Bi⁷⁸⁺. For lead and bismuth the experimental values of the 1s hyperfine splitting are employed to improve significantly the theoretical results by reducing the uncertainty due to the nuclear effects.     

Theoretical calculations of the optical band positions and spin-Hamiltonian parameters for Cr ions in Y2Ti2O7 crystal

The optical band positions and spin-Hamiltonian parameters (g factors g_g_? and zero-field splitting D) for the trigonal Cr³⁺ centers in Y₂Ti₂O₇ crystal are calculated from the complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model. In the calculations, the contributions to spectral data from both the spin-orbit parameter of central dⁿ ion and that of ligand ion are considered and the crystal field parameters used are estimated from the superposition model. The calculated results are in reasonable agreement with the experimental values. The defect structures of Cr³⁺ center is suggested.     

The process Ω→γΞ as a possible test of the penguin diagram

It is argued that Ω→γΞ is a convenient process for testing the ΔS=1 penguin diagram. The analysis is based on the standard pole model, including negative parity resonances. Using bag model matrix elements and standard values of the penguin operator coefficients, it is found that the branching ratio for Ω→γΞ is of order 10^?5 to 10^?4. The weak matrix element for Ω→γΞ estimated by means of soft pion and current algebra techniques is found to be ～7 times bigger than the corresponding bag model result. This implies a branching ratio close to the experimental upper limit if standard values of the penguin coefficients are used.     

Analysis of inclusive nucleon spectra fromp- andα-induced reactions in the frame of the INDEX model,and implications for stopped π−-induced reactions

The previously published INDEX model is tested for nucleon spectra fromp- andα-induced reactions. The results of two alternative versions, the INCLUSIVE INDEX model and the EXCLUSIVE INDEX model, quite well agree with the data. It is found that in the INCLUSIVE INDEX model three preequilibrium stages are sufficient to describe single- and multi-nucleon emission. The model provides an useful first order estimate of the influence of the finite Fermi energy on particle spectra. This effect is very strong for nucleon induced reactions while forα-induced reactions it can be neglected. The deduced mean-free-path multiplier corroborates the long stated discrepancy between models in which excitons interact independently or not. Using preequilibrium parameters similar to those found for nucleon induced reactions the important branching ratio of contributingnp andpp pairs in stoppedπ ^?-absorption can be determined by INDEX model calculations. Deduced values from publishedn- andp-spectra agree reasonably well with those of other experimental analyses but deviate significantly from microscopic model predictions.     

Investigations of the spin-Hamiltonian parameters,optical absorption bands,and local structure for the tetragonal Cu2+ center in Cu2+-doped ZnCdO nanopowder

The spin-Hamiltonian (or EPR) parameters of tetragonal Cu²⁺ octahedral centers in ZnCdO nanopowders are calculated from the high-order perturbation formulas based on the cluster approach. In these formulas, the contributions to spin-Hamiltonian parameters due to the admixture between the d orbitals of dⁿ ion and the p orbitals of ligand ions via covalence effect are considered. The crystal field parameters are calculated from the superposition model and so the optical absorption bands (related to the crystal field energy levels) and local structure of Cu²⁺ octahedral centers in ZnCdO nanopowder are also studied. The calculated spin-Hamiltonian parameters and optical absorption bands are in reasonable agreement with the experimental values. The tetragonal elongation ΔR (=R_//−R_⊥) of Cu²⁺ octahedron in ZnCdO nanopowder due to Jahn–Teller effect is acquired from the calculations. The results are discussed.     

Theoretical analysis of the possible ultra-low-Q-value decay branch of Cs

We have investigated the feasibility of observing an ultra-low-Q-value beta-decay branch of ¹³⁵Cs by applying the microscopic quasiparticle-phonon model with a realistic two-body nuclear interaction. This work was motivated by an earlier combined experimental and theoretical work on decays of ¹¹⁵In. The inaccuracy of the ground-state-to-ground-state Q value limits our ability to draw definite conclusions, and therefore modern precision measurements for it are called for. We present the computed partial half-lives of each channel for the most likely ranges of Q values.     

Low-energy parameters of neutron-neutron interaction in the effective-range approximation

The effect of the mass difference between the charged and neutral pions on the low-energy parameters of nucleon-nucleon interaction in the ¹ S ₀ state is studied in the effective-range approximation. On the basis of experimental values of the singlet parameters of neutron-proton scattering and the experimental value of the virtual-state energy for the neutron-neutron systemin the ¹ S ₀ state, the following values were obtained for the neutron-neutron scattering length and effective range: a _nn = ?16.59(117) fm and r _nn = 2.83(11) fm. The calculated values agree well with present-day experimental results.     

Effect of viscosity on the fission dynamics of the excited compound nucleus 251Es produced in fusion reaction

A stochastic approach based on two-dimensional dynamical model has been used to simulate the fission dynamics of the excited compound nucleus ²⁵¹Es produced in ¹⁹F+²³²Th reaction. In the dynamical calculations the elongation parameter has been used as the first dimension and the projection of the total spin of the compound nucleus onto the symmetry axis, K, considered as the second dimension. The value of post-saddle friction was inferred by reproducing experimental data on the mean pre-scission neutron multiplicity for ²⁵¹Es. It was shown that the results of calculations are in good agreement with the experimental data by applying values of the post-saddle friction equal to 13−15×10²¹s⁻¹.     

Absorption spectrum of trideuteromethane between 7 and 11 μm. Analysis of the ν5 band

The absorption spectrum of trideuteromethane was recorded in the range 900–1400 cm^?1 with a resolution of 0.020–0.025 cm^?1. The ν₅ band centered at 1292.499 cm^?1 is analyzed here. A fit based on 869 observed transitions including J′ values up to 22, leads to a set of spectroscopic constants suitable for energy calculations in the upper-state v₅ = 1. These constants reproduce the experimental wavenumbers with a standard deviation equal to 0.008 cm^?1. The tabulated line strengths are calculated on the basis of the value S = 27.1 cm^?2 atm^?1 at 300 K, measured by Hiller and Straley, for the band strength of ν₅. A useful comparison is made between the values now derived for some constants and the corresponding ones predicted by Gray and Robiette in their recent force field calculations of methane and isotopic species.     

The level structure of 189Os

The level structure of ¹⁸⁹Os has been studied by (d, p), (d, t) and (d, d') reaction spectroscopy at E_d = 12.1 MeV. Assignments of a number of levels at excitation energies below ≈ 1700 keV are given. The assignments are discussed in terms of a unified model based on the Nilsson model including pairing, rotational motion and attenuated Coriolis coupling. Deviations between predicted and experimental excitation energies and wave functions are generally found to be consistent with trends observed in ¹⁸⁷Os and in the odd W isotopes. Evidence for the existence of collective non-rotational states is found from the (d, d') reactions. Results of (³He, α) and high resolution γ-ray and conversion electron studies were also included at various stages of the investigation to supplement the data from the deuteron induced reactions. Comparisons between calculated and measured B(E2) values are found to indicate an intrinsic quadrupole moment of the ground-state band of ≈ 5.0 b, in agreement with values in adjacent even Os isotopes. Details of the Coriolis coupling calculations are given.     

Determination of low-energy parameters of neutron-neutron scattering from an analysis of the binding-energy difference between the 3H and 3He mirror nuclei

A relation between quantities that characterize the breaking of the charge symmetry of nuclear forces in systems of two and three nucleons is found on the basis of an analysis of the binding-energy difference between the ³H and ³He mirror nuclei. For the neutron-neutron scattering length and effective range, the values of a _nn = ?18.38(55) fm and r _nn = 2.84(4) fm, respectively, were obtained by using purely nuclear parameters of proton-proton scattering in the ¹ S ₀ state. The calculated values agree with present-day experimental results.     

Comparison of analyzing power and polarization in the reaction 3H(p,n)3He: (II). New polarization results below 4 MeV

The polarization P^y for the ³H(p, n)³He reaction was measured for energies between 2 and 4 MeV. Special care was given to minimizing the effects of background and to interpreting the experimental spectra. The new values for P^y are significantly higher than previous values, and comparison to the available data for the analyzing power A_y for the same reaction now shows that in this energy range P^y and A_y are equal within experimental uncertainties. This equality negates earlier conclusions that sizeable differences existed between these observables. In particular, our new results demonstrate that in this reaction the effects of charge symmetry breaking on differences between these observables must be small.     

EPR g factors and tetragonal distortion for the isoelectronic Ni and Cu centers in the CuGaSe2 crystal

The EPR g factors, g_|| and g_⊥, for the isoelectronic 3d⁹ ions Ni⁺ and Cu²⁺ at the tetragonal Cu⁺ site of the CuGaSe₂ crystal are calculated from the high-order perturbation formulas based on a two-spin-orbit-parameter model. In the model, both the contributions to g factors from the spin-orbit parameter of central 3d⁹ ion and that of ligand ion are contained. The calculated results appear to be consistent with the experimental values. The tetragonal distortions (characterized by θ−θ₀, where θ is the angle between the metal-ligand bond and C₄ axis, and θ₀≈54.74° is the same angle in cubic symmetry) of Ni⁺ and Cu²⁺ centers, which are different from the corresponding angle in the host CuGaSe₂ crystal and from impurity to impurity, are obtained from the calculations. The difference of the sign of g_||−g_⊥ between the isoelectronic Ni⁺ and Cu²⁺ centers is found to be due to the different tetragonal distortions of both centers in the CuGaSe₂ crystal.     

On the Jones Index Values for Conformal Subnets

We consider the smallest values taken by the Jones index for an inclusion of local conformal nets of von Neumann algebras on S ¹ and show that these values are quite more restricted than for an arbitrary inclusion of factors. Below 4, the only non-integer admissible value is 4 cos² π/10, which is known to be attained by a certain coset model. Then no index value is possible in the interval between 4 and ${3 +\sqrt{3}}$ . The proof of this result is based on α-induction arguments. In the case of values below 4 we also give a second proof of the result. In the course of the latter proof we classify all possible unitary braiding symmetries on the ADE tensor categories, namely the ones associated with the even vertices of the A _n , D _2n , E ₆, E ₈ Dynkin diagrams.