119835686
Connection between the bremsstrahlung tip and direct radiative recombination: angular distributions and polarization correlations
We illustrate the possibility for calculation of bremsstrahlung tip angular distributions and polarization correlations from corresponding photoeffect results with an extension of the method for connecting bremsstrahlung tip and direct-radiative-recombination (DRR) cross sections developed by Lee and Pratt. The agreement between results obtained with this method and results from our numerical partial-wave calculations is, in general, satisfactory. We note features of the distributions and correlations, and once again point out the inadequacies of the nonrelativistic dipole approximation for the evaluation of bremsstrahlung or DRR angular distributions.
121398906
Generalized Fermi-Segrè formula
122939851
Nonstatistical behavior of photoeffect subshell branching ratios at high energies
123462298
Overlap of shape resonance and Cooper-minimum structure in photoionization
Examples of a Cooper minimum inside the range of a shape-resonance maximum of a photoionization cross section have been found in numerical calculations within a single-electron model in a relativistic Hartree-Fock-Slater potential. In these model calculations for the photoionization of tin and uranium we find relatively broad shape resonances in all the $d$ and $f$ subshells. In addition a Cooper minimum occurs in the outer subshells of these high-angular-momentum states within the region of the shape-resonance maximum. We examine the matrix elements for these subshells and the resulting cross sections and angular distributions.
121020837
Observation of zeros and amplification of quadrupole-matrix-element contributions to photoelectron angular distributions
119495662
Direct radiative recombination of electrons with atomic ions: Cross sections and rate coefficients
Simple expressions are obtained which permit systematic estimates of the rate coefficients for direct radiative recombination (DRR) of fast electrons with atomic ions of various ionic species. The analysis utilizes a set of cross sections obtained through numerical calculations combined with the use of an interpolation scheme to smoothly connect reduced cross sections (apart from normalizations) of the bremsstrahlung tip region and the low-lying DRR region. It is shown that these numerical cross sections can be reproduced by the predictions of a modified semiclassical Kramers formula with an appropriate effective charge Z/sub eff/, which is larger than the effective charge which reproduces the energy levels of the states into which capture occurs. In accord with this modified Kramers formula, the numerically obtained total cross sections are shown to scale with Z/sub eff//sup 2//K for each isoelectronic sequence, and with a parameter (n/sub 0/)/sub eff/ which characterizes each isoelectronic sequence. Using these scaling properties, simple analytic expressions are obtained for recombination rate coefficients, for the rate of electron kinetic-energy loss, and for the rate of radiated power loss, assuming a classical Maxwell-Boltzmann thermal distribution of continuum electrons.
120365252
Massless composite particles and space-time description of gauge transformations
Space-time symmetries for massless composite particles are studied within the kinematical framework of the relativistic harmonic-oscillator formalism. It is noted first that the Lorentz-invariant harmonic-oscillator equation is separable in the Kalnins-Miller coordinate system in which the helicity and gauge transformation parameters can be separated from other space-time variables. It is shown then that this separation procedure leads to the representations of the Poincare group which display the same space-time symmetry as those for photons and gravitons. The gauge transformation parameters are shown to be internal space-time parameters in the case of massless composite particles. It is shown in particular that the spin in this case is associated with an orbitlike motion on the plane perpendicular to the momentum of the composite particle.
8523168
Fixed-Point Analysis of the Low-Energy Constants in the Pion-Nucleon Chiral Lagrangian
In the framework of heavy-baryon chiral perturbation theory, we investigate the fixed point structure of renormalization group equations (RGE) for the ratios of the renormalized low energy constants (LECs) that feature in the pion-nucleon chiral Lagrangian. The ratios of the LECs deduced from our RGE analysis are found to be in semi-quantitative agreement with those obtained from direct fit to the experimental data. The naturalness of this agreement is discussed using a simple dimensional analysis combined with Wilsonian RGEs.
119632942
SOLUTIONS OF THE BETHE--SALPETER EQUATION IN THE INFINITE-MOMENTUM LIMIT.
A method is presented for solving the O(3)-invariant integral equation which Kim and Zaoui obtained by taking the infinite-momentum limit of the Bethe-Salpeter equation. A partial-wave decomposition is made for this O(3)-invariant integral equation. A variational method is then developed to solve the resulting radial equation. The solutions of the present analysis give a mass-coupling-constant relation different from that of the solutions obtained by the conventional O(4) method.
124314883
Radial excitations in the symmetric quark model
SummaryRadial excitation modes are analyzed for nonstrange baryons. It is found that the baryon radial mode exhibits a harmonicoscillatorlike mass spectrum with the energy spacing of 270 MeV. It is shown that a largeSU6 force is responsible for this narrow spacing. It is shown also that thisSU6 force is responsible for the exceptionally low mass of the Roper resonance.RiassuntoSi analizzano i modi di eccitazione radiali per barioni non strani. Si trova che il modo radiale del barione presenta un spettro di massa del tipo dell’oscillatore armonico con intervallo di energia di 270 MeV. Si dimostra che una grande forza diSU6 è responsabile di questo piccolo intervallo. Si dimostra anche che questa forza diSU6 è responsabile della massa eccezionalmente bassa della risonanza di Roper.РеэюмеПроводится аналиэ мод радиальных воэбуждений для нестранных барионов. Получается, что барионная радиальная мода обнаруживает массовый спектр, аналогичный спектру гармонического осциллятора, с интервалом 270 МзВ. Покаэывается, что больщаяSU6 сила является ответственной эа зтот уэкий интервал. Также отмечается, что зтаSU6 сила ответственна эа зкспоненциально инэкую массу реэонанса Ропера.
119501690
Lorentz Boosts as Squeeze Transformations and the Parton Picture
It was shown by Gribov, Ioffe, Pomeranchuk in 1966 and by Ioffe in 1969 that a space-time picture is needed for the Lorentz deformation of hadronic interaction region. It is shown that this deformation is a squeeze transformation. It is shown also that Feynman's parton picture emerges as a consequence of Lorentz-squeezed hadrons in the quark model.