PaperPanorama

Nuclear Theory·nucl-th

Monday·April 6, 2015

7 papers—5 primary·2 cross-listed

All7Primary5Cross-lists2
  1. 01

    Kaon and pion parton distribution amplitudes to twist-three

    Chao Shi🇨🇳 · Chen Chen🇨🇳 · Lei Chang🇦🇺 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪 · Hong-Shi Zong🇨🇳

    We compute all kaon and pion parton distribution amplitudes (PDAs) to twist-three and find that only the pseudotensor PDA can reasonably be approximated by its conformal limit expression. At terrestrially accessible energy scales, the twist-two and pseudoscalar twist-three PDAs differ significantly from those functions commonly associated with their forms in QCD's conformal limit. In all amplitudes studied, SU(3) flavour-symmetry breaking is typically a 13% effect. This scale is determined by nonperturbative dynamics; namely, the current-quark-mass dependence of dynamical chiral symmetry breaking. The heavier-quark is favoured by this distortion, for example, support is shifted to the s-quark in the negative kaon. It appears, therefore, that at energy scales accessible with existing and foreseeable facilities, one may obtain reliable expectations for experimental outcomes by using these "strongly dressed" PDAs in formulae for hard exclusive processes. Following this procedure, any discrepancies between experiment and theory will be significantly smaller than those produced by using the conformal-limit PDAs. Moreover, the magnitude of any disagreement will either be a better estimate of higher-order, higher-twist effects or provide more realistic constraints on the Standard Model.

    nucl-thhep-lathep-phnucl-exPRD(2015)·82 citations
  2. 02

    Systematics of capture and fusion dynamics in heavy-ion collisions

    Bing Wang · Kai Wen · Wei-Juan Zhao · En-Guang Zhao · Shan-Gui Zhou

    We perform a systematic study of capture excitation functions by using an empirical coupled-channel model. In this model, a barrier distribution is used to take effectively into account the effects of couplings between the relative motion and intrinsic degrees of freedom. The shape of the barrier distribution is of an asymmetric Gaussian form. The effect of neutron transfer channels is also included in the barrier distribution. Based on the interaction potential between the projectile and the target, empirical formulas are proposed to determine the parameters of the barrier distribution. Theoretical estimates for barrier distributions and calculated capture cross sections together with experimental cross sections of 220 reaction systems with are tabulated. The results show that our empirical formulas work quite well in the energy region around the Coulomb barrier. This model can provide prediction of capture cross sections for the synthesis of superheavy nuclei as well as valuable information on capture and fusion dynamics.

    nucl-thAtom.Data Nucl.Data Tabl.(2017)·65 citations
  3. 03

    The competition between alpha decay and spontaneous fission in odd-even and odd-odd nuclei in the range 99 \leg Z \leg 129

    K. P. Santhosh · B. Priyanka

    The predictions on the mode of decay of the odd-even and odd-odd isotopes of heavy and superheavy nuclei with Z = 99-129, in the range 228 \leg A \leg 336, have been done within the Coulomb and proximity potential model for deformed nuclei (CPPMDN). A comparison of our calculated alpha half lives with the values computed using other theoretical models shows good agreement with each other. An extensive study on the spontaneous fission half lives of all the isotopes under study has been performed to identify the long-lived isotopes in the mass region. The study reveals that the alpha decay half lives and the mode of decay of the isotopes with Z = 109, 111, 113, 115 and 117, evaluated using our formalisms, agrees well with the experimental observations. As our study on the odd-even and odd-odd isotopes of Z = 99-129 predicts that, the isotopes 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127 and 129 survive fission and have alpha decay channel as the prominent mode of decay, these nuclei could possibly be synthesized in the laboratory and this could be of great interest to the experimentalists. The behaviour of these nuclei against the proton decay has also been studied to identify the probable proton emitters in this region of nuclei.

    nucl-thnucl-exNPA(2015)·26 citations
  4. 04

    Scalar Pseudo-Nambu-Goldstone Boson in Nuclei and Dense Nuclear Matter

    Hyun Kyu Lee🇰🇷 · Won-Gi Paeng🇰🇷 · Mannque Rho🇫🇷

    The notion that the scalar listed as in the particle data booklet is a pseudo-Nambu-Goldstone (NG) boson of spontaneously broken scale symmetry, explicitly broken by a small departure from an infrared fixed point, is explored in nuclear dynamics. That notion which puts the scalar -- that we shall identify as a "dilaton" -- on the same footing as the pseudo-scalar pseudo-NG bosons, i.e., octet , while providing a simple explanation for the rule for kaon decay, generalizes the standard chiral perturbation theory (SPT) to "scale chiral perturbation theory," denoted PT, with {\it one infrared mass scale for both symmetries}, with the figuring as a chiral singlet NG mode in non-strange sector. Applied to nuclear dynamics, it is seen to provide possible answers to various hitherto unclarified nuclear phenomena such as the success of one-boson-exchange potentials (OBEP), the large cancellation of strongly attractive scalar potential by strongly repulsive vector potential in relativistic mean field theory of nuclear systems and in-medium QCD sum rules, the interplay of the dilaton and the vector meson in dense skyrmion matter, the BPS skyrmion structure of nuclei accounting for small binding energies of medium-heavy nuclei, and the suppression of hyperon degrees of freedom in compact-star matter.

    nucl-thhep-phPRD(2015)·24 citations
  5. 05

    Fission dynamics within time-dependent Hartree-Fock: deformation-induced fission

    P. M. Goddard · P. D. Stevenson · A. Rios

    Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus, and the daughter products. Purpose: To explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide Pu as an example. Methods: Time-dependent Hartree-Fock calculations based on the Skyrme interaction are used to calculate non-adiabatic fission paths, beginning from static constrained Hartree-Fock calculations. The properties of the dynamic states are interpreted in terms of the nature of their collective motion. Fission product properties are compared to data. Results: Parent nuclei constrained to begin dynamic evolution with a deformation less than the fission barrier exhibit giant-resonance-type behaviour. Those beginning just beyond the barrier explore large amplitude motion but do not fission, whereas those beginning beyond the two-fragment pathway crossing fission to final states which differ according to the exact initial deformation. Conclusions: Time-dependent Hartree-Fock is able to give a good qualitative and quantitative description of fast fission, provided one begins from a sufficiently deformed state.

    nucl-thPRC(2015)·111 citations
  6. 06

    Random Matrix Theory for Transition Strength Densities in Finite Quantum Systems: Results from Embedded Unitary Ensembles

    V.K.B. Kota🇮🇳 · Manan Vyas🇲🇽

    Embedded random matrix ensembles are generic models for describing statistical properties of finite isolated interacting quantum many-particle systems. For the simplest spinless systems, with say particles in single particle states and interacting via -body interactions, we have EGUE() and the embedding algebra is . A finite quantum system, induced by a transition operator, makes transitions from its states to the states of the same system or to those of another system. Examples are electromagnetic transitions (same initial and final systems), nuclear beta and double beta decay (different initial and final systems), particle addition to/removal from a given system and so on. Towards developing a complete statistical theory for transition strength densities, we have derived formulas for lower order bivariate moments of the strength densities generated by a variety of transition operators. For a spinless fermion system, using EGUE() representation for Hamiltonian and an independent EGUE() representation for transition operator, finite- formulas for moments up to order four are derived, for the first time, for the transition strength densities. Formulas for the moments up to order four are also derived for systems with two types of spinless fermions and a transition operator similar to beta decay and neutrinoless beta decay operators. Moments formulas are also derived for transition operator that removes number of particles from fermion system. Numerical results obtained using the exact formulas for two-body () Hamiltonians (in some examples for ) and the asymptotic formulas clearly establish that in general the smoothed form of the bivariate transition strength densities take bivariate Gaussian form for isolated finite quantum systems. Extensions of these results to bosonic systems and EGUE ensembles with further symmetries are discussed.

    ↳ quant-phmath-phmath.MPnucl-thAnnals Phys.(2015)·14 citations
  7. 07

    Double bremsstrahlung from high-energy electron in the atomic field

    P.A. Krachkov🇷🇺 · R. N. Lee🇷🇺 · A. I. Milstein🇷🇺

    The differential cross section of double bremsstrahlung from high-energy electron in the electric field of heavy atoms is derived. The results are obtained with the exact account of the atomic field by means of the quasiclassical approximation to the wave functions and the Green's function in the external field. It is shown that the Coulomb corrections to the differential cross section (the difference between the exact result and the result obtained in the leading Born approximation) correspond to small momentum transfers. The Coulomb corrections to the differential cross section of double bremsstrahlung are accumulated in the factor, which coincides with the corresponding factor in the differential cross section of single bremsstrahlung. At small momentum transfer, this factor is very sensitive to the parameters of screening while the Coulomb corrections to the spectrum have the universal form.

    ↳ hep-phnucl-thphysics.atom-phPRA(2015)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE