共查询到20条相似文献,搜索用时 31 毫秒
1.
The s-wave η self-energy in the nuclear medium is calculated in a chiral unitary approach. A coupled channel Bethe–Salpeter equation is solved to obtain the effective ηN interaction in the medium. The base model reproduces well the free space πN elastic and inelastic scattering at the ηN threshold or N*(1535) region. The Pauli blocking on the nucleons, binding potentials for the baryons and self-energies of the mesons are incorporated, including the η self-energy in a self-consistent way. Our calculation predicts about −54−i29 MeV for the optical potential at normal nuclear matter for an η at threshold but also shows a strong energy dependence of the potential. 相似文献
2.
CHEN Bao-Qiu 《中国物理C(英文版)》1993,17(4):345-352
In Dirac-Brueckner calculations for nuclear matter,the average binding energy per nucleon versus density curve is not uniquely defined if coupling to anti-particle is neglected.According to the Hugenholtz-Van Hove theorem,a constraint requires that the nucleon separation energy equals to the fermi energy at saturation density.Choosing saturation energy as empirical value EB/A=-15.8MeV,the self-consistent calculation leads to the saturation density kf=1.41fm-1 and effective mass m*=0.52m,in compressive coefficient k=208MeV.Applying the first law of thermodynamics,self-consistent effective mass (real scalar potential) and the binding energy per nucleon as function of the nuclear density can be obtained.With the realistic nucleon-nucleon interaction (Bonn potential),the vector potential can be obtained from solving the RBBG equation,which weakly depends on the momentum.The cross section and spin observables of the nucleon-nucleus scattering are studied with this new self-consistent relativistic microscopic optical potential. 相似文献
3.
We study the rôle of semiclassical QCD vacuum solutions in high-energy scattering by considering the instanton contribution to hadronic cross sections. We propose a new type of instanton-induced interactions (“instanton ladder”) that leads to the rising with energy cross section σsΔ of Regge type (the pomeron). We argue that this interaction may be responsible for the structure of the soft pomeron. The intercept Δ>0 is calculated. It has a nonanalytic dependence on the strong coupling constant, allowing a nonsingular continuation into the nonperturbative region. We derive the pomeron trajectory, which appears to be approximately linear in some range of (negative) momentum transfer t, but exhibits a curvature at small t. Possible rôle of instantons in multiparticle production is also discussed. 相似文献
4.
We present a new method for the approximate solution of the Bethe-Goldstone equation when it has a singular kernel. The method reduces the integral equation to a set of coupled differential equations which are easily solved. In the special case of binding energy calculations, non-singular kernel, our method is equivalent to the reference spectrum method. A particular advantage is that there is no ambiguity in the treatment of hard-core N-N interactions. We perform calculations both for the Hamada-Johnston and Reid hard-core internucleon potentials and in intermediate states always use self-consistent single-particle energies. We apply the method to calculate in nuclear matter the binding energy/nucleon and the nucleon optical potential. Our results for the binding energy differ by about 2 MeV from those published for similar calculations. The difference is a consequence of our use of self-consistent energies and a greater number of partial waves, L ≦ 4. For the optical potential we obtain a logarithmic variation with incident energy E for E > 100 MeV, in agreement with experimental data. We also obtain better agreement with experiment than other authors for the energy variation in the the range 40 MeV < E < 100 MeV. This improvement is a consequence of our use of a higher number of partial waves. 相似文献
5.
M. Nekipelov M. Bü scher W. Cassing M. Hartmann V. Hejny V. Kleber H. R. Koch V. Koptev Y. Maeda R. Maier S. Merzliakov S. Mikirtychiants H. Ohm A. Petrus D. Prasuhn F. Rathmann Z. Rudy R. Schleichert H. Schneider K. Sistemich H. J. Stein H. Str her K. -H. Watzlawik C. Wilkin 《Physics letters. [Part B]》2002,540(3-4):207-212
The ratio of forward K+ production on copper, silver and gold targets to that on carbon has been measured at proton beam energies between 1.5 and 2.3 GeV as a function of the kaon momentum pK using the ANKE spectrometer at COSY-Jülich. The strong suppression in the ratios observed for pK<200–250 MeV/c may be ascribed to a combination of Coulomb and nuclear repulsion in the K+A system. This opens a new way to investigate the interaction of K+-mesons in the nuclear medium. Our data are consistent with a K+A nuclear potential of VK0≈20 MeV at low kaon momenta and normal nuclear density. Given the sensitivity of the data to the kaon potential, the current experimental precision might allow one to determine VK0 to better than 3 MeV. 相似文献
6.
M. S. Shikakhwa 《International Journal of Theoretical Physics》2007,46(2):405-416
The structure of the interaction Hamiltonian in the first order S-matrix element of a Dirac particle in an Aharonov-Bohm (AB) field is analyzed and shown to have interesting interesting algebraic
properties. It is demonstrated that as a consequence of these properties, this interaction Hamiltonian splits both the incident
and outgoing waves in the the first order components (eigenstates of the third component of the spin). The matrix element can then be viewed as the sum of two transitions
taking place in these two channels of the spin. At the level of partial waves, each partial wave of the conserved total angular
momentum is split into two partial waves of the orbital angular momentum in a manner consistent with the conservation of the
total angular momentum quantum number. 相似文献
7.
C. J. Horowitz K. S. Kumar R. Michaels 《The European Physical Journal A - Hadrons and Nuclei》2014,50(2):1-13
We analyze microscopic many-body calculations of the nuclear symmetry energy and its density dependence. The calculations are performed in the framework of the Brueckner-Hartree-Fock and the self-consistent Green’s functions methods. Within Brueckner-Hartree-Fock, the Hellmann-Feynman theorem gives access to the kinetic energy contribution as well as the contributions of the different components of the nucleon-nucleon interaction. The tensor component gives the largest contribution to the symmetry energy. The decomposition of the symmetry energy in a kinetic part and a potential energy part provides physical insight on the correlated nature of the system, indicating that neutron matter is less correlated than symmetric nuclear matter. Within the self-consistent Green’s function approach, we compute the momentum distributions and we identify the effects of the high momentum components in the symmetry energy. The results are obtained for the realistic interaction Argonne V18 potential, supplemented by the Urbana IX three-body force in the Brueckner-Hartree-Fock calculations. 相似文献
8.
In three-dimensional QED, which is analyzed in the 1/N expansion, we obtain a sufficient and necessary condition for a nontrivial solution of the Dyson–Schwinger equation to be chiral symmetry breaking solution. In the derivation, a normalization condition of the Goldstone bound state is used. It is showed that the existent analytical solutions satisfy this condition. 相似文献
9.
研究了原子在光晶格偶极势依赖原子动量情况下的运动, 特别考虑了偶极势对原子动量的依赖特性. 对动量和位置的方差研究表明, 原子的动量方差呈现压缩性质, 位置方差呈现放大性质.据此我们预言光晶格动量依赖偶极势中的单粒子态可能接近动量压缩线态. 研究结果还表明, 红失谐情况下原子的动量演化可分为三个过程: 第一个过程是慢减速过程, 初始动量较大的原子, 动量以近似阻尼振荡的形式衰减; 第二个过程是快减速过程, 当动量被减速到接近到光子动量时, 动量迅速减小到hk(Ω/γ)2, 其中hk为光子动量, Ω为拉比频率, γ为原子波函数衰减函数; 第三个过程是原子被囚禁过程, 当原子动能被降低到小于势井深度时, 原子被囚禁在晶格波腹附近.
关键词:
动量演化
光晶格
压缩态 相似文献
10.
M. Chartier J. R. Beene B. Blank L. Chen A. Galonsky N. Gan K. Govaert P. G. Hansen J. Kruse V. Maddalena M. Thoennessen R. L. Varner 《Physics letters. [Part B]》2001,510(1-4):24-28
The proton-stripping reaction from a 11Be radioactive beam incident on a beryllium target demonstrates that only (7±3)% of the 9Li residues in the reaction are in coincidence with the 2.7 MeV γ-ray corresponding to the 9Li first excited state. This implies that the previously observed low-energy neutrons from the decay of the unbound nucleus 10Li represent a direct l=0 transition to the 9Li ground state. Consequently, neutron-unbound 10Li is proven to have the same parity inversion as occurs in the case of 11Be with a
intruder state below the natural parity
state. 相似文献
11.
12.
Nonlinear spatiotemporal dynamics of carrier densities in Gunn diodes under impact ionization conditions is numerically investigated using a set of model partial differential equations. Numerical results show that a multidomain regime emerges as a result of the decrease in domain size caused by impact ionization, and that the spatiotemporal evolution of the domains becomes chaotic in the presence of strong impact ionization. 相似文献
13.
We discuss some infinite matter properties of two finite-range interactions widely used for nuclear structure calculations, namely Gogny and M3Y interactions. We show that some useful informations can be deduced for the central, tensor and spin–orbit terms from the spin–isospin channels and the partial wave decomposition of the symmetric nuclear matter equation of state. We show in particular that the central part of the Gogny interaction should benefit from the introduction of a third Gaussian and the tensor parameters of both interactions can be deduced from special combinations of partial waves. We also discuss the fact that the spin–orbit of the M3Y interaction is not compatible with local gauge invariance. Finally, we show that the zero-range limit of both families of interactions coincides with the specific form of the zero-range Skyrme interaction extended to higher momentum orders and we emphasize from this analogy its benefits. 相似文献
14.
The barriers standing against the formation of superheavy elements and their consecutive decay have been determined in the quasimolecular shape path within a Generalized Liquid Drop Model including the proximity effects between nucleons in a neck, the mass and charge asymmetry, a precise nuclear radius and the shell effects given by the Droplet Model. For moderately asymmetric reactions double-hump potential barriers stand and fast fission of compact shapes in the outer well is possible. Very asymmetric reactions lead to one hump barriers which can be passed only with a high energy relatively to the superheavy element energy. Then, only the emission of several neutrons or an particle can allow to reach an eventual ground state. For almost symmetric heavy-ion reactions, there is no more external well and the inner barrier is higher than the outer one. Predictions for partial decay half-lives are given. 相似文献
15.
The interplay between quantization and topology is investigated in the frame of a topological model of electromagnetism proposed by the author. In that model, the energy of electromagnetic radiation in a cubic cavity is
where d is a topological integer index equal to the degree of a map between two orbifolds. 相似文献
16.
An approach which makes the first order pion-nucleus optical potential theoretically sound is presented. This study should permit higher order improvements to the potential to be more meaningful and the nuclear structure information extracted from pi-nucleus scattering to be more reliable. Based on multiple scattering theory, three optical potentials are constructed and studied in momentum space. These models are the popular Kisslinger potential, the local “Laplacian” potential, and an “improved off-shell potential;” the latter one is derived from absorptive separable pion-nucleon potentials which exactly reproduce on-shell πN scattering. By working in momentum space and explicitly including πN resonances and off-shell effects in the definition of the optical potential, the approach described here is capable of handling any number of pi-nucleon partial waves, is applicable over a very wide energy region, is based on a physical model for off-shell behavior, and is extended easily to include higher order effects. The optical potentials are inserted into two different relativistic wave equations to determine the total cross section and elastic differential cross section for pi-nucleus scattering. It is found that the various models for off-shell πN scattering determine significantly different πC12 scattering, with the improved off-shell model preferred on theoretical grounds. Also discussed is the importance of properly transforming πN scattering to the pi-nucleus c.m. system, the origin of the shift in the peak position of the π?C total cross section, and the reason for the increased diffractive nature of the differential cross section at 180 MeV. 相似文献
17.
A nonlocal energy-dependent self-consistent kaon-nucleus optical potential is derived for kaonic atoms. Energy level shifts and widths are calculated for several light nuclei, and the results are compared with experiment. The sensitivity of the results to changes in parameters of the nuclear matter distribution is studied. Nonlocality and off-energy-shell effects are examined.The optical potential is derived by means of a Brueckner-type many-body theory with the independent pair approximation for the kaon and the nucleon. The two-body interaction on which the optical potential depends is represented by separable potentials of the Yamaguchi form. Coupled channels ( and Σπ) are used for the I = 0 states, which are dominated by the resonance, and only a single channel () is used for the I = 1 state.Calculations are carried out in three levels of approximation of the nonlocal energy-dependent optical potential. In no approximation is the potential found to be proportional to the nuclear density. Indeed, the real part of the potential changes sign in the nuclear surface. Sensitivity of the results to variations in the nuclear matter distribution is investigated and found to be on the order of experimental error. Nonlocality and off-energy-shell effects are estimated to be at least as large as this error, so that these effects must be included if one wishes to extract information about the nuclear surface from the existing experimental data. The use of correct nucleon wavefunctions and binding energies is similarly found to be essential in the calculation. 相似文献
18.
In this paper, we obtain reliable expressions to calculate the barrier and pocket positions of the real part of the effective
phenomenological optical potential having Woods-Saxon form factor, for different partial waves. The comparison of the results
obtained from these formulae, when compared with the numerical results obtained using Newton-Raphson iterative procedure are
found to be quite accurate, with error less than 1%. We also obtain algebraic expressions for estimatingl
poc, the angular momentum at which the potential pocket vanishes, the accuracy of which is tested with the exact calculations,
using self-consistent iterative procedures. These and other expressions deduced in this paper provide simple and useful methods
for calculating critical parameters of heavy ion effective potentials like barrier and pocket positions, curvatures at the
barrier and pocket positions,l
poc and the grazing angular momentuml
g to carry out the analysis of heavy ion scattering. 相似文献
19.
The liquid–gas phase transition in hot neutron-rich nuclear matter is investigated within a self-consistent thermal model using an isospin and momentum dependent interaction (MDI) constrained by the isospin diffusion data in heavy-ion collisions, a momentum-independent interaction (MID), and an isoscalar momentum-dependent interaction (eMDYI). The boundary of the phase-coexistence region is shown to be sensitive to the density dependence of the nuclear symmetry energy with a softer symmetry energy giving a higher critical pressure and a larger area of phase-coexistence region. Compared with the momentum-independent MID interaction, the isospin and momentum-dependent MDI interaction is found to increase the critical pressure and enlarge the area of phase-coexistence region. For the isoscalar momentum-dependent eMDYI interaction, a limiting pressure above which the liquid–gas phase transition cannot take place has been found and it is shown to be sensitive to the stiffness of the symmetry energy. 相似文献
20.
J. I. Prisciandaro P. F. Mantica B. A. Brown D. W. Anthony M. W. Cooper A. Garcia D. E. Groh A. Komives W. Kumarasiri P. A. Lofy A. M. Oros-Peusquens S. L. Tabor M. Wiedeking 《Physics letters. [Part B]》2001,510(1-4):17-23
An 879.9(2) keV γ-ray transition has been identified following the β decay of 58V and assigned as the 2+1→0+1 transition in 58Cr34. A peak in the energies of the first excited 2+ states for the even–even chromium isotopes is now evident at 56Cr32, providing empirical evidence for a significant subshell gap at N=32. The appearance of this neutron subshell closure for neutron-rich nuclides may be attributed to the diminished π1f7/2–ν1f5/2 monopole proton–neutron interaction as protons are removed from the 1f7/2 single-particle orbital. 相似文献