带有两个重夸克的重子谱计算中几个困难问题的研究

由两个重夸克和一个轻夸克组成的重子可以看作是一个两体系统.它的两个重夸克组成一个玻色型的双夸克团.利用B–S方程导出了它的轻夸克和重的双夸克之间的等效相互作用势.在利用这种势计算重子质量的过程中,发现有几个困难问题需要深入探讨.它们是:(1)算符排序,(2)由非相对论展开带来的误差,(3)自旋–自旋耦合,(4)在标量双夸克组成的重子态和矢量双夸克组成的重子态之间的混合.本文详细地讨论并适当地处理了这些问题.     

Radiative leptonic decay Bc^-→τ^vτ^-γ in the standard model and the two-Higgs-doublet model

We analyze the radiative leptonic Bc decay Bc^-→τ^vτ^-γ in the Standard Model and the two- Higgs-doublet model using the non-relativistic constituent quark model. The results confirm that this channel is experimentally promising in view of the large number of Bc mesons which are expected to be produced at future hadron facilities. We also find that this decay is sensitive to the parameters of the two-Higgs-doublet model, and it can be tested in future experiments.     

Vacuum fluctuation effects on hyperonic neutron star matter

The vacuum fluctuation （VF） effects on the properties of the hyperonic neutron star matter are investigated in the framework of the relativistic mean field （RMF） theory. The VF corrections result in the density dependence of in-medium baryon and meson masses. We compare our results obtained by adopting three kinds of meson-hyperon couplings. The introduction of both hyperons and VF corrections softens the equation of state （EoS） for the hyperonic neutron star matter and hence reduces hyperonic neutron star masses. The presence of the δ field enlarges the masses and radii of hyperonic neutron stars. Taking into account the uncertainty of meson-hyperon couplings, the obtained maximum masses of hyperonic neutron stars are in the range of 1.33M⊙-1.55M⊙.     

pp final state interaction in J/ψ →γpp

The phenomenon of the near ppˉ-threshold enhancement observed in the J/ψ→γ pp decay is studied by using the enhancement factor method with a simpler one-pion-exchange potential between p and p. The Jost function caused by the mentioned potential is perturbatively calculated in the zero-th order approximation, and the corresponding enhancement factor is obtained. It is found that such a final state interaction offers an important contribution to the decay width near the ppˉ-threshold, although it is not large enough. To explain the decay data, a phenomenological factor G(p) with the form of 285500/(m 2 π + p 2 ) should be introduced. A further calculation including the p-dependent bare T -matrix, a more realistic N ˉ N potential and the contribution from the higher-order wave functions would provide a better understanding of the decay data and even the existence of the baryonium ppˉ. The near ppˉ-threshold behavior of the decay width in the J/ψ→π 0 pp process is also discussed.     

Chiral Extrapolation of Lattice Data of Λ_b→Λ_c Form Factors

An extrapolation to the physical limit for the lattice data of Λ_b →Λ_c form factors computed in the nonphysical region is made in this work through a class of fitting functions proposed by us with nonlinear dependence on m2/π derived in the chiral perturbative theory(ChPT) and the heavy quark effective theory(HQET) framework. Then the results are applied to calculate the differential and integrated Λ_b →Λ_c semileptonic decay rates. Meanwhile, a comparison between our results and those obtained through the extrapolation functions with naive linear dependenceon m2/π is made.It is shown that the difference between the extrapolated central values of these two cases is about 5%.The total uncertainties(depending on the momentum transfer q~2) in the linear case are about 5% ～10%(caused by the uncertainties of lattice data) and those in the nonlinear case are about 10% ～ 20%(caused by the uncertainties of both lattice data and input parameters in Ch PT and HQET). More accurate lattice data and parameters in ChPT and HQET are needed to reduce the uncertainties of the extrapolated results.     

超新星中微子

 根据中外天文学史专家对东方、阿拉伯和欧洲大量古代记载的分析,在望远镜发明之前,人类历史上记录可靠的超新星共有七颗,它们出现的时间和星座分别为:185年在半人马座、393年在天蝎座、1006年在豺狼座、1054年在金牛座、1181年在仙后座、1572年在仙后座、1604年在蛇夫座。     

Possible heavy dibaryons

In the framework of the constituent quark model, the possible S-wave heavy dibaryon states with the c flavor are investigated. The factors which are responsible for the binding behavior of the dibaryon system are analyzed. It is shown that both the symmetry character of the system and the energy of interactions between interacting quarks are important for the binding behavior of the two-baryon system with the heavy flavor. As a result, seven possible candidates of heavy dibaryons with c flavor are predicted.     

Supernova neutrino detection on earth

In this paper, we first discuss the detection of supernova neutrinos on earth. Then we propose a possible method to acquire information about θ13 smaller than 1.5° by detecting the ratio of the event numbers of different flavor supernova neutrinos. Such an sensitivity cannot yet be achieved by the Daya Bay reactor neutrino experiment.     

Direct CP violation in B(s)→J/ψP(V)

In the framework of factorization, we study direct CP violation in the decays of B_(s)→J/ψP(V) (P(V) refer to the pseudoscalar (vector) meson). The CP violation depends strongly on Cabibbo-Kobayashi- Maskawa (CKM) matrix elements and the effective parameter, N_c. The recent experimental data for the branching ratios of B_(s)→J/ψP(V) are accurate enough and we can give a strong constraint on the range of N_c. We nd that the CP violating asymmetry is consistent with the available experiment values for the b→d transition, and a little smaller than the b→s transition. We also predict the CP violation of other decay channels for B_(s)→J/ψP(V). We expect our results can give valuable guidance for experiments.     

Electron-Positron Pair Production in an Arbitrary Polarized Ultrastrong Laser Field

Electron-positron pair production in an arbitrary polarized ultrastrong laser field is investigated in the first order perturbation approximation in which the Volkov states are used for convenient calculation of scattering amplitude and cross section. It is found surprisingly that the optimal pair production depends strongly on the polarization. For some cases of field parameters, the optimal field is elliptically polarized or evenly circularly polarized one, rather than the usual linear polarization as indicated by previous works. Some insights into pair generation are given and some interesting unexpected features are also discussed briefly.