最小seesaw模型对氚β衰变和无中微子双β衰变的限制

在最小seesaw模型下计算了氚β衰变的有效质量〈m〉_e以及无中微子双β衰变的有效质量〈m〉_ee. 利用最新的中微子振荡数据, 在正质量等级情况下得到了0.00424eV≤〈m〉_e≤0.0116eV和0.00031eV≤〈m〉_ee0.0052eV; 如果中微子的质量谱是倒质量等级情况, 能够得到0.0398eV≤〈m〉_e≤0.0571eV和0.0090eV≤〈m〉_ee≤0.0571eV.最后还讨论了最小的中微子混合角和Majorana CP破坏位相对〈m〉_ee的影响.     

跷跷板模型中三阶中微子混合矩阵的幺正性破坏

对标准模型的一种简单扩充就是引入n个重的右手中微子且保持其SU(2)_L×U(1)_Y规范对称性. 通过对角化(3+n)×(3+n)阶中微子质量矩阵, 得到关于ν_e, ν_μ和ν_τ的有效 质量矩阵的精确的解析表达式. 结果表明, 在轻子带电弱流中出现的3×3中微子混合矩阵V必须不是严格幺正的. 如果通过跷跷板机制产生正确的轻的中微子的质量标度, 那么V的幺正性破坏的程度非常小, 几乎可以忽略. 类似的结论同样可以在第二类跷跷板模型中得到.     

中微子质量矩阵和中微子转换矩阵间的一种可能的关系

我们探讨了以ν_e,ν_μ,ν_τ为基的, 具有一种新的对称性的中微子质量矩阵M. 首先在没有T(时间)破坏的前提下, 假定该质量矩阵具有一个简单的三参数形式. 这一矩阵确定了3种中微子的质量m₁, m₂, m₃以及使M对角化的转换矩阵U. 因为无T破坏的U给出3个可测量参数s₁₂, s₂₃, s₁₃, 我们的形式用3个参数表示6个可测量的物理量, 其结果与实验数据符合得很好. 更精确的测量将对模型给出严格的检验, 并确定这3个参数的值. 本文还推广讨论了包含T破坏的情况.     

中微子质量与宇宙超大尺度结构

由>10²Mpc的宇宙超大尺度结构推知我们的宇宙委可能主要是由热暗物质(中微子)所组成,其质量m_v～10^－1eV(0.16eV).     

Ds衰变常数的测量

利用北京谱仪在e⁺e^－对撞质心能量4.03GeV所取得的约22.3pb^－1的数据,用先标记μ,后标记D_s的方法,共找到2个D_s→μv,3个D_s→τv→μvvv衰变候选事例,给出了D_s的纯轻子衰变的绝对分支比为:Br(D_s→μv)+0.72+0.70－0.44),Br(D_s→τv)=(14+11－8)%,并给出不依赖于模型假设的D_s衰变常数为:f_Ds=(355+96+28－90－28)MeV.     

高能νN“弹性”反应的中间玻色子效应

利用中间玻色子理论和Cabibbo的弱相互作用SU₃模型,求得了中微子-核子“弹性”反应ν₁+N→l+B的微分截面和终态粒子纵极化的解析表式,并对若干过程进行了数值计算。结果表明:对给定的一组形状因子,当中微子能量足够高时,在适当的出射角附近,轻子和超子的纵极化的中间玻色子效应相当明显;如实验数据足够精确,将极化与微分截面相结合。可估计中间玻色子质量,并给出形状因子的一些知识。还估计了ν_μ[Z,A]→μ^-+[Z+1,A]过程的μ^-纵极化的核效应和中微子能谱的影响。     

48Ca无中微子双β衰变的寿命下限

本文报道国内首次开展的双β衰变实验研究工作.国产大尺寸CaF₂闪烁晶体既用来做为探测器,又做为双β衰变的放射源.数据采集总共7588.5小时.实验给出⁴⁸Ca无中微子双β衰变的寿命下限T_1/2>1.1×10²²年(68%C.L.);由理论推算相应的中微子质量v≤8eV;右手流混合参量η的限值η≤0.69×10^－5.     

中微子几何混合模型与轻子和重子数产生

在这一报告中将报告我和BABU教授合作的在hep-ph/0507217一文中有关中微子混合研究结果. 目前中微子实验数据所决定的混合角可归结为几何混合状况:sin²θ₁₂=1/3,sin²θ₂₃=1/2, 和sin²θ₁₃=0. 我们在这一工作中建立了能实现这一几何混合的可重整化模型. 模型以非阿贝尔非连续群A₄为描述中微子不同代混合的对称性. 这类模型对中微子质量有很强的限制. 而且能很自然地由轻子数破坏产生重子不对称的实验观测值. 很有趣的是这类模型中出现在轻子不守恒和无中微子双beta衰变中的相位是一样的.     

ELECTRONIC AND OPTICAL PROPERTIES OF WURTZITE GaN:——A THEORETICAL APPROACH

The band structures of wurtzite GaN(α-GaN) are studied using the nearest and second-nearest neighbour semi-empirical tight-hinding method in sp³ s^* model. The calculated direct fundamental gap of α-GaN is 3.45 eV, which is in good agreement with the experimental data. The density of states and the imaginary pert of dielectric function (ε₂ (ω)) are evaluated to he in the regions - 10.0 - 12 eV and (1.0 - 10.0 eV, respectively. There are mainly three peaks at 6,4, 7,5, 8.4 eV, dominating the ε₂(ω) spectrum. The two components of the ε₂(ω) (i. e. ε_2xy(ω) and ε_2z(ω) ) are also calculated; and the real prat of dielectric function, reflectivity, absorption coefficient, and refractive index are all studied.     

5(6)羧基荧光素敏化TiO2纳米粒子的光致电子转移的荧光特性研究

通过水解TiCl₄制备了锐钛矿结构TiO₂纳米粒子, 并用时间分辨荧光光谱研究了5(6)CFL(5(6)-Carboxyfluorescein, 简称5(6)CFL)染料敏化TiO₂纳米粒子体系的光致电子转移动力学. 5(6)CFL染料敏化TiO₂纳米粒子能形成电荷转移复合物, 这归因于染料分子的激发电子态波函数Ψ(D^*)与电荷分离态波函数Ψ(D⁺ +e^-)之间的耦合作用. 当激发5(6)CFL染料敏化TiO₂纳米粒子体系时, 电子以两种不同方式注入TiO₂纳米粒子导带: 第一, 通过5(6)CFL染料分子的激发态注入; 第二, 从电荷转移复合物(5(6)CFL/TiO₂)直接注入. 时间分辨荧光光谱表明, 在水溶液中纯5(6)CFL染料的荧光以寿命为τ₁=41 ps (74.4%) 和τ₂=3.22 ns (25.6%) 的双e指数衰减, 而5(6)CFL染料敏化TiO₂纳米粒子体系的荧光分别以时间常数为τ₁=44 ps (90.4%), τ₂=478 ps (8.6%) 和τ₃=2.41 ns (1.0%) 的三e指数衰减. 本文的研究工作能够为染料敏化太阳能电池的光致电子转移机理提供有价值的参考.     

Bounds on neutrino mixing with exotic singlet neutrinos

We examine the effects of mixing induced non-diagonal light-heavy neutrino weak neutral currents on the amplitude for the process (with a=e, μ or τ). By imposing constraint that the amplitude should not exceed the perturbative unitarity limit at high energy , we obtain bounds on light-heavy neutrino mixing parameter sin² where is the mixing angle. In the case of one heavy neutrino (mass mξ) or mass degenerate heavy neutrinos, for Λ=1 TeV, no bound is obtained for mξ<0.50 TeV. However, sin² ≤3.8 × 10⁻⁶ for mξ=5 TeV and sin ≤6.0 × 10⁻⁸ for mξ=10 TeV. For Λ=∞, no constraint is obtained for mξ<0.99 TeV and sin² ≤3.8 × 10⁻² (for mξ=5 TeV) and sin² ≤9.6 × 10⁻³ (for mξ=10 TeV).     

Impacts of dark energy on constraining neutrino mass after Planck 2018

Considering the mass splittings of three active neutrinos, we investigate how the properties of dark energy affect the cosmological constraints on the total neutrino mass $\sum {m}_{\nu }$ using the latest cosmological observations. In this paper, several typical dark energy models, including ΛCDM, wCDM, CPL, and HDE models, are discussed. In the analysis, we also consider the effects from the neutrino mass hierarchies, i.e. the degenerate hierarchy (DH), the normal hierarchy (NH), and the inverted hierarchy (IH). We employ the current cosmological observations to do the analysis, including the Planck 2018 temperature and polarization power spectra, the baryon acoustic oscillations (BAO), the type Ia supernovae (SNe), and the Hubble constant H₀ measurement. In the ΛCDM+$\sum {m}_{\nu }$ model, we obtain the upper limits of the neutrino mass $\sum {m}_{\nu }\lt 0.123\,\mathrm{eV}$ (DH), $\sum {m}_{\nu }\lt 0.156\,\mathrm{eV}$ (NH), and $\sum {m}_{\nu }\lt 0.185\,\mathrm{eV}$ (IH) at the 95% C.L., using the Planck+BAO+SNe data combination. For the wCDM+$\sum {m}_{\nu }$ model and the CPL+$\sum {m}_{\nu }$ model, larger upper limits of $\sum {m}_{\nu }$ are obtained compared to those of the ΛCDM+$\sum {m}_{\nu }$ model. The most stringent constraint on the neutrino mass, $\sum {m}_{\nu }\lt 0.080\,\mathrm{eV}$ (DH), is derived in the HDE+$\sum {m}_{\nu }$ model. In addition, we find that the inclusion of the local measurement of the Hubble constant in the data combination leads to tighter constraints on the total neutrino mass in all these dark energy models.     

Compactification of patterns by a singular convection or stress

A wide variety of propagating disturbances in physical systems are described by equations whose solutions lack a sharp propagating front. We demonstrate that presence of particular nonlinearities may induce such fronts. To exemplify this idea, we study both dissipative u_{t}+ partial differential_{x}f(u)=u_{xx} and dispersive u_{t}+ partial differential_{x}f(u)+u_{xxx}=0 patterns, and show that a weakly singular convection f(u)=-u;{alpha}+u;{m}, 0相似文献   

Oxygen chemisorption and initial oxidation of Cr(110)

The initial stages of the interaction of oxygen with a Cr(110) surface have been investigated at 300 K by LEED, AES, electron energy loss spectroscopy (ELS), secondary electron emission spectroscopy (SES) and work-function change measurement (Δφ). In the exposure region up to 2 L, the clean-surface ELS peaks due to interband transition weakened and then disappeared, while the ～5.8 and 10 eV loss peaks attributed to the O 2p → Cr 3d transitions appeared, accompanied with a work-function increase (Δφ = +0.19 eV at2L). In the region 2–6 L the work function decreased to below the original clean-surface value (Δφ_min = ?0.24 eV at6L), and five additional ELS peaks were observed at ～2, 4, 11, 20 and 32 eV: the 2 and 4 eV peaks are ascribed to the ligand-field d → d transitions of a Cr³⁺ ion, the 11 eV peak to the O 2p → Cr 4s transition, the 20 eV peak to the Cr 3d → 4p transition of a Cr³⁺ ion and the 32 eV peak probably to the Cr 3d → 4f transition. A new SES peak at 6.1 eV, being attributed to the final state for t he 11 eV ELS peak, was observed at above 3 L and identified as due to the unfilled Cr 4s state caused by charge transfer from Cr to oxygen sites in this region. In the region 6–15 L the work function increased again (Δφ_max = +0.32 eV at15 L), the 33 and 46 eV Auger peaks due to respectively the M_2,3(Cr)L_2,3(O)L_2,3(O) cross transition and the M_2,3VV transition of the oxide appeared and the 26 eV ELS peak due to the O 2s → Cr 4s transition was also observed. Above 10 L, the ELS spectra were found to be practically the same as that of Cr₂O₃. Finally, above 15 L, the work function decreased slowly (Δφ = +0.13 eV at40L). From these results, the oxygen interaction with a Cr(110) surface can be classified into four different stages: (1) dissociative chemisorption stage up to 2 L, (2) incorporation of O adatoms into the Cr selvedge between 2–6 L, (3) rapid oxidation between 6–15 L leading to the formation of thin Cr₂O₃ film, and (4) slow thickening of Cr₂O₃ above 15 L. The change in the Cr 3p excitation spectrum during oxidation was also investigated. The oxide growth can be interpreted on the basis of a modified coupled current approach of low-temperature oxidation of metals.     

Correlation time and diffusion coefficient imaging: application to a granular flow system

A parametric method for spatially resolved measurements for velocity autocorrelation functions, R(u)(tau) = , expressed as a sum of exponentials, is presented. The method is applied to a granular flow system of 2-mm oil-filled spheres rotated in a half-filled horizontal cylinder, which is an Ornstein-Uhlenbeck process with velocity autocorrelation function R(u)(tau) = e(- ||tau ||/tau(c)), where tau(c) is the correlation time and D = tau(c) is the diffusion coefficient. The pulsed-field-gradient NMR method consists of applying three different gradient pulse sequences of varying motion sensitivity to distinguish the range of correlation times present for particle motion. Time-dependent apparent diffusion coefficients are measured for these three sequences and tau(c) and D are then calculated from the apparent diffusion coefficient images. For the cylinder rotation rate of 2.3 rad/s, the axial diffusion coefficient at the top center of the free surface was 5.5 x 10(-6) m(2)/s, the correlation time was 3 ms, and the velocity fluctuation or granular temperature was 1.8 x 10(-3) m(2)/s(2). This method is also applicable to study transport in systems involving turbulence and porous media flows.     

Nuclear Responses for Neutrinos and Mo Observatory of Neutrinos

Nuclear responses for neutrinos and neutrino studies in Mo nuclei are briefly reported. Nuclear spin-isospin responses for neutrinos are crucial for neutrino studies in nuclei. Spin-isospin responses for solar neutrinos, supernova neutrinos and neutrinos involved in double-beta decays are discussed. It is of great interest to study neutrino masses and low energy solar neutrinos. It is shown that it is possible to carry out with ¹⁰⁰Mo both spectroscopic studies of double-beta decays with the sensitivity of the order of m 0.03eV and real-time exclusive studies of the low energy solar neutrinos.     

Hydrogen above saturation at silicon vacancies: H-pair reservoirs and metastability sites

We propose that hydrogen-passivated multivacancies which appear to be fully saturated with H can actually capture additional H in electrically inactive sites. In silicon, first-principles total energy calculations show that splitting an (m>or=2) multivacancy into a mono- and an (m-1) vacancy provides a low-strain pairing site for H, 0.4 eV per H lower than any known bulk pairing site. This monovacancy ejection mechanism is an excellent candidate for the H reservoir found both in crystalline and amorphous Si. A distinct H pairing on the fully saturated m vacancies, by forming an internal surface Si-Si dimer, provides the final state of light-induced metastable degradation of hydrogenated amorphous silicon.     

Multidimensional compactons

We study the two and three dimensional, N=2, 3, nonlinear dispersive equation CN(m,a+b): u(t)+(u(m))x + [u(a)inverted delta2ub]x=0 where the degeneration of the dispersion at the ground state induces cylindrically and spherically symmetric compactons convected in the x direction. An initial pulse of bounded extent decomposes into a sequence of robust compactons. Colliding compactons seem to emerge from the interaction intact, or almost so.     

Combined effects of donor and acceptor impurities on the thermoelectric properties of cadmium antimonide

A study was made of the effect of the simultaneous doping with donor (Te) and acceptor (Cu, Ag, Au) elements on the thermoelectric properties of CdSb. Doping with tellurium changes the p-type conductivity of the CdSb crystals to an n-type conductivity with an impurity (Te) activation energy of E_d = (0. 11 ± 0. 01) eV. Doping with an acceptor impurity changes the energy of the donor level, by E_d = 0. 14 eV for doping with silver, by E_d = 0. 10 eV for doping with gold and by E_d = 0. 095 eV for doping with copper. It is shown that the type of conductivity and the thermoelectric properties of CdSb can be adjusted in the desired direction through simultaneous doping with two impurities.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 90–94, June, 1970.     

Positron-lithium scattering with the inclusion of positronium formation

Detailed studies have been made of elastic scattering and positronium formation in low energy collisions of positrons with lithium atoms for the two partial wavesl=0,1. For this system, as for all alkali atoms, the positronium formation channel is open even at zero positron energy. A two-channel version of the Kohn variational method is used with trial functions containing many variational parameters, and reasonably well converged results are obtained. The s-wave positronium formation cross section is infinite at zero positron energy but it then falls rapidly to become several orders of magnitude smaller than the elastic scattering cross section which has a maximum value of approximately 100 ₀ ² at a positron energy of 0.5 eV. For p-wave scattering the positronium formation cross section rises to a value of approximately 10 ₀ ² at an energy of 0.1 eV, with the elastic scattering cross section rising to a maximum of approximately 60 ₀ ² just below the first excitation threshold at 1.84 eV.