122812048
Nucleon effective mass in symmetric nuclear matter from the extended Brueckner- Hartree-Fock approach *
We have calculated the nucleon effective mass in symmetric nuclear matter within the framework of the Brueckner-Bethe-Goldstone (BBG) theory, which has been extended to include both the contributions from the ground-state correlation effect and the three-body force (TBF) rearrangement effect. The effective mass is predicted by including the ground-state correlation effect and the TBF rearrangement effect, and we discuss the momentum dependence and the density dependence of the effective mass. It is shown that the effect of ground state correlations plays an important role at low densities, while the TBF-induced rearrangement effect becomes predominant at high densities.
118506081
Three-body force effect on the properties of nuclear matter under the gap and continuous choices within the BHF approach
We have calculated and compared the three-body force effects on the properties of nuclear matter under the gap and continuous choices for the self-consistent auxiliary potential within the Brueckner-Hartree-Fock approach by adopting the Argonne V-18 and the Bonn B two-body potentials plus a microscopic three-body force (TBF). The TBF provides a strong repulsive effect on the equation of state of nuclear matter at high densities for both the gap and continuous choices. The saturation point turns out to be much closer to the empirical value when the continuous choice is adopted. In addition, the dependence of the calculated symmetry energy upon the choice of the self-consistent auxiliary potential is discussed.
119110371
Three-body force effect on off-shell mass operator and spectral functions in nuclear matter
Within the framework of the Brueckner theory, the off-shell behaviors of the mass operator $M(k,\omega)=V(k,\omega)+iW(k,\omega)$, i.e., its dependence upon the momentum $k$ and upon the nucleon frequency $\omega$, are investigated by including nuclear three-body force (TBF). The first two terms of the hole-line expansion of the mass operator are taken into account. The TBF effects on their off-shell properties are discussed. A comparison is made between the on-shell and off-shell values of $M_{1}$. The nucleon spectral function and nucleon momentum distribution are also calculated, and the calculation shows that they are hardly affected by the TBF effect at the saturation density. At a high density two times greater than the saturation density, inclusion of the TBF may lead to a visible effect on the spectral function and may enhance the depletion of the hole states.
118833038
Transport parameters in neutron stars from in-medium NN cross sections
We present a numerical study of shear viscosity and thermal conductivity of symmetric nuclear matter, pure neutron matter, and beta-stable nuclear matter, in the framework of the Brueckner theory. The calculation of in-medium cross sections and nucleon effective masses is performed with a consistent two- and three-body interaction. The investigation covers a wide baryon density range as needed in the applications to neutron stars. The results for the transport coefficients in beta-stable nuclear matter are used to make preliminary predictions on the damping time scales of nonradial modes in neutron stars.
15459179
Probing the isospin dependent in-medium nucleon–nucleon cross section by nucleon emissions
The effects of the symmetry potential and the isospin dependent in-medium nucleon-nucleon (NN) cross section on the number of proton(neutron) emissions N-p(N-n) are studied respectively within an isospin-dependent quantum molecular dynamics (IQMD) model. The isospin dependent in-medium NN cross section is found to have a strong influence on Np (Nn) but Np(Nn) is not sensitive to the symmetry potential for the neutron-deficient colliding system at relatively high energies. We propose to make use of the N-p(N-n) as a probe to extract information on the isospin dependent in-medium NN cross section. (C) 2002 Elsevier Science B.V. All rights reserved.
119275256
Effects of the magnetic field on the spallation reaction implemented by BUU coupled with a phase-space coalescence afterburner
Based on the Boltzmann-Uehling-Uhlenbeck (BUU) transport model coupled with a phase-space coalescence afterburner, the spallation reaction p + 197Au at the incident beam energy Ebeam = 800 MeV/nucleon is studied. We find that the number of test particles per nucleon has minor effects on the neutron-to-proton ratio (n/p) of the produced heavier fragments while it affects much their yields. The external strong magnetic field affects the production of heavier fragments more than the n/p of produced fragments. The n/p of free nucleons is greatly affected by the strong magnetic field, especially for the nucleons with lower energies.
122357291
UNPARTICLE PHYSICS AND NEUTRAL MESON MIXING
The concept of exact and broken scale invariance is discussed. We give a brief introduction to unparticle physics. The neutral meson mixing can be caused by exchange of unparticle at the tree level. The constraints on interaction between unparticle and SM quarks are discussed.
119716730
A twist-4 effect in the parton evolution processes
Recently, a research group reported that they can fit the F2 data well by using the Altarelli-Parisi evolution equation with a valence-like initial gluon distribution, which means that we need not consider the high twist effects in the proton. In this letter, we point out that their valence-like initial gluon distribution is unreasonable for the proton structure function. With the reasonable initial distributions, we find that the high twist corrections to the Altarelli-Parisi evolution equation is necessary.
124490688
THE VIRTUAL EXCHANGE OF PSEUDOSCALAR MESONS IN THE MIT BAG MODEL
In this paper the virtual exchange effect of pseudoscalar mesons in the MIT bag model is discussed and the mass spectrum of hadrons, the magnetic moments and the mean square values of charge radius are calculated. It is pointed out that our model can preserve and improve the static properties of the MIT bag model and provide an explanation for the origin of the meson cloud outside baryons.
121884540
The Structure Function of Six-Quark Cluster and the EMC Effect
Based upon the experiments on electric form factor for deutron use is made of the valon model to determine the valon distribution functions in a six-quark cluster. By using the QCD evolution equation, the dependence of the structure function of a six-quark cluster is obtained. The EMC effect is discussed and it is pointed out that the distortion of the nucleon structure function in nuclei may be ascribed to the contributions from the six-quark cluster(for ) and the meson cloud(for ).
15594064
The Factorization in exclusive B decays: A Critical look
I review the theoretical ideas and concepts along the line of factorization in the exclusive B decays. In order to understand the naive factorization, the effective field theories and the perturbative method of QCD are introduced and developed. We focus our discussions on the large energy effective theory, the QCD factorization approach and the soft-collinear effective theory.