共查询到20条相似文献,搜索用时 15 毫秒
1.
We study the υμ and υγ decays in the early epoch of the universe. If mυγ > 2me, there would be a CP asymmetry between υγ→e++e-+υe and υγ→e++ e-+ υe. The resultant CP non-invariance is a function of temperature and density and can reach l0-7 for a reasonable temperature range, but it is noticed that if mυγ > 2υμ~200 MeV, the CP non-invariance can be much larger. 相似文献
2.
Mujahid Kamran 《理论物理通讯》1995,23(3):379-382
Using perturbative QCD in conjunction with CVC and standard electroweak theory, it is shown that at large Q2, F1n/F1P = F2n/F1P = -0.69. The comparison with other results on form factor ratios from QCD sum rules and/or PQCD is carried out. 相似文献
3.
WANGHong-Min ZHANGBen-Ai 《理论物理通讯》2004,42(5):735-738
The constituent quarks in the nucleon have always been considered as a point-like particle in the relativisticconstituent quark model. However its calculation results of GE^n agree poorly with the new experimental data. Theelectromagnetic structure of light front constituent quarks is considered in this paper. We find that the calculationresults have good agreement with the new experimental data of GE^n after considering the contribution of the quarkstructure term. This treatment seems to be able to improve the fit to experimental data of GEp/GMp,√Q2F2p/kpF1p,and GEn/GMn as well. 相似文献
4.
The Fokker-Planck coefficients for Coulomb interaction, or the friction coefficient (Δυα) (the average change in velocity) and the diffusion coefficient (ΔυαΔυα), are evaluated by an appropriate variable change technique. This approach reduces the five-fold integral expressions of the Fokker-Planck coefficients to one-fold integral without meeting the divergence difficulties. A new Debye cutoff parameter Δυαmin, instead of the customary θmin cutoff avoids the error incurred through the customary neglecting of velocity dependence of the Coulomb logarithm. The dominant terms of the new results are similar to Chandrasekhar's results. A non-dominant term, which can exceed the dominant one in the case of υα2 > υβt2lnA is added for (Δυα||2). 相似文献
5.
ZHOU BangRong 《理论物理通讯》1999,32(3):425-434
The gap equation at finite temperature in the top-quark condensate scheme of electroweak symmetry breaking is proven to have the identical form in both the imaginary and real time formalisms of thermal field theory. By means of the gap equation, combined with the basic relation to define the vacuum expectation value v of the effective Higgs field, we analyze the dependence on temperature T and chemical potential p of the dynamical top-quark mass as the order parameter characteristic of symmetry breaking, and obtain the p-T criticality curve for symmetry restoration. We find out that the critical temperature Tc = 2υ for μ = 0 and the critical chemical potential μc = 2 π υ / √3 for T = 0. When μ = 0, the top-quark mass near Tc has the leading (Tc2 - T2)1/2 behavior with an extra factor dependent on temperature T and the momentum cutoff Λ. However, it is generally argued that the symmetry restoration at T ≥ Tc is still a second-order phase transition. 相似文献
6.
7.
It is shown that the expansion and summation of the divergent series occurring in 2υ-2β decay calculation[1,2] can be well-defined without mathematical flaw. 相似文献
8.
N.Ghahramany G.R.Boroun 《理论物理通讯》2003,40(5):551-557
A calculation of the proton structure function F2(x,Q^2) is reported with an approximation method that relates the reduced cross section derivative and the F2(x, Q^2) scaling violation at low x by using quadratic form for the structure function. This quadratic form approximation method can be used to determine the structure function F2 (x, Q^2) from the HERA reduced cross section data taken at low x. This new approach can determine the structure functions F2(x,Q^2) with reasonable precision even for low x values which have not been investigated. We observe that the Q^2 dependence is quadratic over the full kinematic covered range. To test the validity of our new determined structure functions, we find the gluon distribution function in the leading order approximation with our new calculation for the structure functions and compare them with the QCD parton distribution functions. 相似文献
9.
VO2表面氧缺陷的存在对VO2材料具有显著的电子掺杂效应, 极大地影响材料的本征电子结构和相变性质. 通过2, 3, 5, 6-四氟-7, 7', 8, 8'-四氰二甲基对苯醌(F4TCNQ)分子表面吸附反应, 可以有效消除表面氧缺陷及其电子掺杂效应. 利用同步辐射光电子能谱和X射线吸收谱原位研究了修复过程中电子结构的变化以及界面的化学反应, 发现这种方式使得VO2薄膜样品氩刻后得到的V3+失去电子成功地被氧化成原先的V4+, 同时F4TCNQ分子吸附引起电子由衬底向分子层转移, 界面形成带负电荷的分子离子物种. 受电化学性质的制约, F4TCNQ分子吸附反应修复氧缺陷较氧气氛退火更安全有效, 不会引起表面过度氧化形成V2O5. 相似文献
10.
以聚乙烯亚胺(PEI)为表面活性剂,采用水热合成法,制得了表面氨基修饰的水溶性β-NaY(Gd)F4:Yb3+/Er3+纳米棒,并对β-NaY(Gd)F4:Yb3+/Er3+上转换纳米棒的制备方法、条件等进行了考察.结果表明,当Gd3+的引入摩尔分数为40%时,200 ℃下反应8 h即可获得纯β-NaY(Gd)F4:Yb3+/Er3+纳米棒.利用X射线粉末衍射仪(XRD)、扫描电子显微镜 (SEM)、透射电子显微镜(TEM)、荧光光谱(PL)对样品的结构、形貌及光谱特性进行了表征.结构和形貌分析结果表明,制得的样品为单相β-NaY(Gd)F4:Yb3+/Er3+纳米棒,纳米棒的截面粒径约为40 nm,平均长度约为210 nm.在980 nm波长激发下,样品的上转换发光光谱中出现了4个发射中心位于407,529,546,660 nm的发射带,分别对应于Er3+离子的2H9/2→4I15/2、2H11/2→4I15/2、4S3/2→4I15/2和4F9/2→4I15/2跃迁.采用戊二醛法,使β-NaY(Gd)F4:Yb3+/Er3+上转换纳米棒表面的氨基与牛血清蛋白(BSA)分子中的氨基成功偶连在一起.利用紫外光谱分析(UV)和考马斯亮蓝法,对二者的偶联进行了证明. 相似文献
11.
12.
According to a uniform and simple method
of calculating spin-lattice coupling coefficients and the perturbation
formulas of gi factors and hyperfine structure constants
Ai based on the cluster approach for 3d7 ions in cubic, tetragonal and trigonal octahedral crystal fields, the spin-lattice coupling coefficients Fij (F11, F12, F44), Zij (Z11, Z12, Z44) and also
g factor and hyperfine constant A for MgO:Co2+ are calculated
by using the parameters obtained from the optical spectra without adjustable parameters. The calculated results
show good agreement with the observed values. The difficulty
in explaining the coefficients
Fij and Zij is therefore removed. 相似文献
13.
The form of the universal scaling law of the critical dynamic exponent, z = Dƒ + 2/υ, is found on a family of regular fractals by the exact TDRG method. Here, we generate a regular fractal by an anisotropic growing process. Identifying the growing probabilities as the interactions between Ising spins on the fractals, we map the growing probability clouds as a group of the anisotropic Ising Hamiltonians. Applying the RG transformations, we find that the systems of this group of Ising Hamiltonians can be described by two universal static correlation exponents υ0 = ∞ and υ = 1. So, the growing processes proposed by us capture the essential features in the directed DLA simulations. The studies about their critical dynamic behaviours reveal that unlike the one-dimensional chain the critical dynamics of the kinetic Ising model on the regular fractals is universal. The further discussions show that there is a universal scaling law form of the critical dynamic exponent of the kinetic Ising model, z = Dƒ + Rmax/2υ, on the site models of the regular fractals with Rmin = 2. Meanwhile, we discuss Daniel Kandal's correction to the formula of the,critical dynamic exponent in the TDRG method and show that our TDRG calculations are exact. 相似文献
14.
Using some limiting procedures, the solutions of the fifth order KdV equation ut + (μu2+ υuxx + αuuxx + βux2 + γu3 + δuxxxx)x = 0 would degenerate into the solutions of a simple equation, say KdV equation. In this letter, we analyze the possibility of the inverse procedure of the limiting process mentioned above for the travelling wave solutions. The results show that the procedure for deforming a travelling wave solution of the KdV equation to that of the generalized fifth order KdV equation can be accomplished by some pure algebraic tricks. Moreover, this inverse procedure is not unique in general. 相似文献
15.
A unified calculation of the whole energy spectrum and g factors of the ground stateat normal pressure and their pressure-induced shifts for α-A12O3:Ni2+ has been carried outon the basis of the theory of pressure-induced shifts and the diagonalization of the completed8 energy matrix adopting C3υ symmetry. The calculated results are in very good agreementwith all the experimental data. The rates of change of all the levels with respect to variousparameters and the contributions to typical levels or splittings from various parameters havebeen calculated. The distinct differences of pressure-induced shifts of various levels are immediatelydetermined by their characteristic dependencies on -the parameters of interactions,and the pressure-induced shifts (especially those of t26e2 1EÊ) have provided important or,crucial criteria for the correctness of the calculation and assignment of the energy spectrum of α-A12O3:Ni2+. 相似文献
16.
In the paper, we apply the kT factorization approach to deal with the Bs → f0 (980) transition form factors in the large recoil regions, i.e. the small q 2 regions. For the purpose, we adopt the B-meson wave-functions ΨB , ΨB and δ that include the three-Fock states contributions to do our discussion. Although the scalar meson f0 (980) is widely perceived as the 4-quark bound state (scenario 2), but the distribution amplitudes of 4-quark states are still unknown to us, so we adopt 2-quark model (scenario 1) for scalar meson f0 (980) in our discussion. By varying the B-meson wave-function parameters within their reasonable regions, we obtain F0(0) = F+(0) = 0.20 ± 0.02, FT(0) = 0.24 ± 0.02. Our present results for these form factors are consistent with the light-cone sum rule results obtained in the literature. 相似文献
17.
We discuss in this paper the possible contributions from IRρ (ρ-reggeon associated with ρ meson) in DIS process on protons. Using results from phenomenological analysis of high energy π-N charge-exchange scattering process, we get the expression of effective propagator of IRρ and the coupling constant βρ between IRρ and light quarks. As a simple and concrete example, we use them to evaluate the contributions of ρ to F2(χ, Q2) from charge-exchange photoproduction quark-pair process, γ* + p → n + qu + qd(→ n + X), in HERA kinematical regions. For comparison, we also evaluate contributions both from pomeron and partons in the same process. The ratio of contributions in F2(χ, Q2) from IRρ versus IP is larger than 1%, therefore, the former may be tested experimentaly. 相似文献
18.
WANG Zhi-Gang 《理论物理通讯》2015,63(4):466-480
In this article, we calculate the contributions of the vacuum condensates up to dimension-10 in the operator product expansion, and study the C γμ- Cγνtype scalar, axial-vector and tensor tetraquark states in details with the QCD sum rules. In calculations, we use the formula μ = (M 2X/ Y /Z-(2Mc)2)~(1/2) to determine the energy scales of the QCD spectral densities. The predictions MJ =2=(4.02+0.09-0.09) GeV, MJ =1=(4.02+0.07-0.08) GeV favor assigning the Zc(4020) and Zc(4025) as the JP C= 1+-or 2++diquark-antidiquark type tetraquark states, while the prediction M++J =0=(3.85+0.15-0.09) GeV disfavors assigning the Z(4050) and Z(4250) as the JP C= 0diquark-antidiquark type tetraquark states. Furthermore, we discuss the strong decays of the 0++, 1+-, 2++diquark-antidiquark type tetraquark states in details. 相似文献
19.
S. Platchkov A. Amroun S. Auffret J. M. Cavedon P. Dreux J. Duclos B. Frois D. Goutte H. Hachemi J. Martino X. H. Phan
I. Sick
《Nuclear Physics A》1990,510(4):740-758We have measured the deuteron A(Q2) structure function in the momentum transfer region between 1 and 18 fm−2. The accuracy of the data ranges from 2 to 6%. These measurements allow a sensitive test of theoretical predictions. We find that meson-exchange currents and relativistic corrections significantly improve the agreement between experiment and theory. We investigate the sensitivity of A(Q2) to the nucleon-nucleon interaction and to the neutron electric form factor GEn(Q2). Our analysis shows that GEn(Q2) can be extracted from these data with a significantly improved accuracy. The model dependence of this analysis is discussed. 相似文献
20.
In this paper, we generalize the systematic approximation and the systematic adiabatic approximation developed by G. Schöner and H.aken[1,2] to the stochastic systems driven by O-U noises. After eliminating the fast variables st, we introduce a new family of stochastic processes Kt(υ) (υ≥2) in the equations for the order parameters vt. A typical model serves to illustrate how to derive the equation for the order parameter and how to calculate the statistical properties of the new stochastic processes Kt(υ) (υ≥2). Some significant discussions and conclusions are given in Sec. V. 相似文献