Universal ZN-graded differential calculus

We investigate the propeties of differential algebras generated by an operator d satisfying the property d^N = 0 instead of d² = 0 as in the usual case. Several examples of realizations of such differential algebras are given, either in the context of Z_N-graded N × N matrix algebras, or as a generalized differential calculus on manifolds.     

GUT breaking on M×T/(Z2×Z2′)

We construct two SU(5) models on the space–time M⁴×T²/(Z₂×Z₂′) where the gauge and Higgs fields are in the bulk and the Standard Model fermions are on the brane at the fixed point or line. For the zero modes, the SU(5) gauge symmetry is broken down to SU(3)×SU(2)×U(1) due to non-trivial orbifold projection. In particular, if we put the Standard model fermions on the 3-brane at the fixed point in model II, we only have the zero modes and KK modes of the Standard Model gauge fields and two Higgs doublets on the observable 3-brane. So, we can have the low energy unification, and solve the triplet–doublet splitting problem, the gauge hierarchy problem, and the proton decay problem.     

On the electroweak and gluonic corrections to the hadronic width of the Z boson

The electroweak corrections to the Z-boson hadronic width are presented in a simple analytical form for the width itself, Λ_h, for its ratio to the leptonic width, R_l = Λ_h/Λ_l, for the Λ_b/Λ_h ratio, and for the total width Λ_Z. The rational parametrization, advocated in our recent papers on leptonic decays, simplifies the analysis of the hadronic decays too. There are two main results of this analysis: (1) All electroweak precision measurements agree within 1 σ with the electroweak Born approximation if the gluon coupling constant . Thus the electroweak radiative corrections have not been observed experimentally. The unexpected smallness of electroweak radiative corrections is caused by the mutual cancellation of the large positive contribution of a heavy top quark and the large negative contribution of all other virtual particles. (2) With electroweak radiative corrections being taken into account, the value of extracted from the experimental value of Λ_Z differs by 3σ from that obtained from R_l, if m_t 200 GeV; they agree within 1σ if m_t 150 GeV. Thus a low upper limit on m_t can be obtained from hadronic decays of the Z-boson alone, even without data on its leptonic decays.     

Z′ mediated flavor changing neutral currents in B meson decays

We study the effects of an extra U(1)′ gauge boson with flavor changing couplings with fermion mass eigenstates on certain B meson decays that are sensitive to such new physics contributions. In particular, we examine to what extent the current data on B_d→φK and B_d→η′K decays may be explained in such models, concentrating on the example in which the flavor changing couplings are left-chiral. We find that within reasonable ranges of parameters, the Z′ contribution can readily account for the anomaly in S_φKS but is not sufficient to explain large branching ratio of B_d→η′K with the same parameter value. S_φKS and S_η′KS are seen to be the dominant observables that constrain the extra weak phase in the model.     

Measurement of L X-ray production cross sections and Li subshell fluorescence yields

L_i (i=1, 2 and 3) X-ray production cross sections have been measured for 14 elements in the atomic number range 55≤Z≤81 at 15.73 keV. The values of L_i subshell fluorescence yields (ω₁, ω₂ and ω₃) have been determined using the presently measured X-ray production cross sections and the theoretical L_i subshell photoionization cross sections values, Coster–Kronig transition probabilities and radiative emission rates. The measured X-ray production (XRP) cross-sections and fluorescence yield values were compared with the theoretical and semi empirical values, respectively.     

Ba1-xB2-y-zO4SixAlyGaz晶体和频可调谐深紫外飞秒激光器

介绍了一种基于新型非线性晶体Ba_1-xB_2-y-zO₄Si_xAl_yGa_z 的可调谐深紫外飞秒激光光源. 从理论上分析了基频光和倍频光在通过非线性晶体时所造成的空间走离和群速度失配, 为了补偿空间走离以及波长调谐过程中晶体折射造成的光束偏离现象, 将两块相同的倍频晶体成镜像放置来产生二次谐波. 并调节延迟线的长度来补偿基频光和倍频光之间的群速度失配, 从而提高和频转换效率. 然后通过和频方式进行三倍频和四倍频来突破晶体相位匹配条件的限制, 产生了波长低于200 nm的深紫外飞秒激光. 利用钛宝石激光器提供基频光光源, 最终在250–300 nm, 192.5–210 nm 范围内获得了高重频、可调谐超短脉冲紫外和深紫外激光. 并在基频光波长为800 nm时, 得到的二倍频、三倍频和四倍频的功率分别为1.28 W, 194 mW和5.8 mW, 相对于前一级的转换效率依次为46.14%, 15.16%和3%. 采用互相关法测量得到266.7 nm紫外激光的脉冲宽度约为640.4 fs.     

Magnetization measurements of Fe1−xCoxSi

Magnetization measurements are made in pulsed magnetic fields up to 200 kOe at 4.2 K and up to 100 kOe at various temperatures on the alloys Fe_1−xCo_xSi. In the paramagnetic region of x<0.05 or x0.7, we expected a metamagnet transition at high field but no remarkable change of magnetization is observed.     

Itinerant magnetism in TiMxBe2-x (M = Cu, Fe)

Magnetization and Mössbauer studies of TiCu_xFe_yBe_2-x-y (x = 0, 0.03, 0.4, y = 0, 0.02) show that TiBe₂ is an enhanced paramagnet, 0.02 Fe or 0.03 Cu reduce the susceptibility. On the other hand, TiCu_0.4Be_1.6 is ferromagnetic (T_c = 20 K) and 0.02 Fe reduces the magnetization and Curie point (T_c = 16 K). The magnetic properties of all samples are extremely sensitive to sample preparation and heat treatments.

The Mössbauer studies show that the itinerant magnetism resides on the Ti site, all Ti sites have the same local spin density irrespective of local environment.     

Magnetic properties of the Bi1.95Sr2.05−xLaxCuOy (Bi-2201) superconducting phase

We have investigated the reversible mixed-state magnetization M of three lanthanum substituted Bi_1.95Sr_2.05−xLa_xCuO_y (Bi-2201) ceramic samples having different critical temperatures T_c ranging from 20.0 to 35.5 K. As for the Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) phase, we found that anisotropy of Bi-2201 is large. A manifestation of this anisotropy is the field independent magnetization M^* observed at a temperature T^*. In the framework of the London model, and including thermal fluctuations of vortices, we found for the temperature dependence of the penetration depth λ_ab(T) = λ_ab(0)[1 − (T/T_c0)ⁿ]^−1/2, with n 1.7 and λ_ab (T = 0) 4000 Å. The estimated upper critical fields μ₀H_c2,c are of the order of 10 T. We observe a peculiar negative slope M/T at low temperature and sufficiently high external magnetic field. This feature seems to be a characteristic of the Bi-2201 phase. However, we do not know whether it is associated with the superconducting mixed-state. A small amount of magnetic impurities could also be responsible for this behavior. Finally, the behavior of the reversible magnetization of the Bi-2201 samples investigated, which are situated at the optimal and in the overdoped region, did not indicate any unusual temperature dependence for the upper critical field H_c2,c.     

Magnetic properties of Gd2(Fe1−x−yCoyTix)17

Serial single-phase Gd₂(Fe_1−x−yCo_yTi_x)₁₇ compounds have been synthesized. These compounds have a crystal structure belonging to rhombohedral lattice with space group. The lattice parameters of compounds decrease with cobalt content and increase with titanium content, respectively. The saturation magnetization decreases with increasing cobalt and titanium contents. The anisotropy fields increase to maximum then decrease with cobalt concentration. The magnetocrystalline anisotropy constants increase with cobalt content from negative to positive maximum and then decrease with Co concentration. The saturation moment of the compounds decreases linearly with cobalt concentration and decreases nonlinearly with titanium concentration.     

Magnetic properties of Gd2Fe14−xCoxB compounds

The magnetization of magnetically-aligned Gd₂Fe_14−xCo_xB samples with x = 0, 2, 4, 6, 8.4, 11.2 and 14 has been measured at 4.2 K in fields up to 14 T and the anisotropy fields have been derived. The effect of substitution of Co for Fe on the magnetic properties of Gd₂Fe₁₄B has been investigated.     

Mo,Ta, W在NixAl1-x(x=0.25,0.5,0.75) 中的择优占位

用多体势结合分子动力学计算了L1₂型NiAl₃, L1₂型Ni₃Al, L1₀型NiAl和B₂ 型NiAl的晶格常数, 结合能以及合金形成热; 分析了结构性点缺陷在上述四种合金中的存在形式; 在此基础上研究了合金化元素Mo, Ta, W在Ni_xAl_1-x(x=0.25,0.5,0.75)中的择优占位行为. 计算结果表明: 对于四种结构的Ni-Al合金, 偏离理想化学配比时,主要的结构缺陷形式是反位置; 根据占位能最小化, 第三组元元素Mo, Ta, W在上述四种Ni-Al中都显著优先占据Al格位. 关键词： 多体势 Ni-Al合金 占位     

Luminescence from Si-Si1−xGex/Si1−yCy-Si structures

Near band edge photoluminescence has been obtained from Si_1−yC_y quantum well (QW) and neighboring Si_1−xGe_x/Si_1−yC_y double QW (DQW) structures. Enhanced no-phonon recombination is observed from the DQW structures and it is attributed to a breaking of the k-selection rule in the presence of the heterointerface. The luminescence persists for measurement temperatures up to 30–50 K and the intensity exhibits a quenching behavior with an activation energy equal to 8–20 meV. In electroluminescence only recombination in the Si_1−xGe_x layer has been observed from neighboring Si_1−xGe_x and Si_1−yC_y DQW structures.     

Spin-freezing processes around the tricritical point in Mn1−xTixSb

Transitions related to the spin-glass phase in Mn_1−xTi_xSb are revisited from the nonlinear ac susceptibility. Near the tricritical point (x≈0.8), the transition between ferromagnetic and reentrant spin-glass states is sharp. At x0.8, an anomally is found slightly above the temperature of usual spin-glass freezing.     

Measurements of the spin correlation parameters Axx and Ayy for p-p scattering at 46.9 MeV

The A_xx and A_yy spin correlation coefficients of proton-proton scattering have been measured at E_lab = 46.9 MeV and θ_c.m. = 90° with the same experimental techniques already used at Saclay from 11 to 26 MeV and at Grenoble at 37.2 MeV. For A_xx the deviation from the predictions of the energy-dependent phase-shifts analysis of Livermore is significant (≈ 3.7 standard deviations) but not as large as for the 47.5 MeV Tokyo measurement. For A_yy the agreement is very good.     

Measurement of the spin correlation parameters Axx and Ayy for proton-proton scattering at 47.5 MeV

A measurement of the spin correlation parameters A_xx(90° cm) and A_yy(90° cm) of 47.5 MeV proton-proton scattering has been performed by means of polarized beam and a polarized target.     

Hyperfine fields at Y nuclei in Y(Fe1−xTx)3 (T = Al, Co)

The spin echo spectra of ⁸⁹Y hyperfine fields in Y(Fe_1−xT_x)₃ with low concentration x consist of two main lines and of satellite lines caused by the replacement of the Fe atoms by the T atoms. Values of the magnetic moments of the T atoms are estimated by observing the satellite lines.     

Negative luminescence from In1−xAlxSb and CdxHg1−xTe diodes

Indium aluminium antimonide (In_1−xAl_xSb) and cadmium mercury telluride (Cd_xHg_1−xTe) heterostructure diodes, which comprise a near intrinsic active region bounded by more highly doped contact regions, exhibit positive or negative luminescence at medium to long infrared wavelengths when forward or reverse biased respectively at room temperature. In reverse bias, the carrier densities in the near intrinsic region are reduced below their equilibrium values by the effects of exclusion and extraction. In consequence, the radiative recombination is reduced and the devices emit less infrared radiation than the thermal equilibrium value. The observed intensity of the negative luminescence is in general agreement with expected values.     

NMR study of hyperfine interactions in R1−xLuxFe2 (R = Gd, Tb)

Spin-echo NMR measurements on ¹⁵⁵Gd, ¹⁵⁹Tb and ¹⁷⁵Lu have been done for the cubic Laves phase compounds Gd_1−xLu_xFe₂ and Tb_1−xLu_xFe_x. The observed hyperfine fields of Gd and Lu in those compounds increase with increasing Lu concentration. The concentration dependence of the Lu hyperfine field is qualitatively discussed.     

Photo- and electro-production of narrow exotic states: From light quarks to charm and up to bottom

Accessing a full image of the inner content of hadrons represents a central endeavour of modern particle physics, with the main scientific motivation to investigate the strong interaction binding the visible matter. On the one hand, the structure of known exotic candidates is a fundamental open issue addressed widely by scientists. On the other hand, looking for new states of exotic nature is a central component for theoretical and experimental efforts from electron-positron machine and electron accelerator with fixed target to heavy ion and electron-ion colliders. In this article we present a succinct short overview of the attempt to search for exotic narrow N^∗ and Z states containing light quarks only or also charm, and its connotation for bottom regions (the latter two are also known as P_c (Z_c) and P_b (Z_b) states, respectively in the literature). We address the effort of searching for exotic narrow N^∗ and Z states in light quark sector. We focus on recent progress in searching for signal of P_c and Z_c states photoproduction and its implication into the P_b and Z_b photoproduction and their decay properties. We also discuss future perspectives for the field in electron-ion colliders, a good place to disentangle the nature of some of these states and investigate some other enlightening topics including QCD trace anomaly and quarkonium-nucleon scattering length.