Theory of core-level spectroscopy in f and d electron systems

A review is presented of many body effects in core-level spectroscopy (CLS) of f and d electron systems from a theoretical point of view. Historical developments and the most recent topics in this field are described. The impurity Anderson model (IAM) has been successfully applied to the analysis of X-ray photoemission spectra (XPS) and X-ray absorption spectra (XAS) in f and d electron systems, where the f and d electron states are treated as being on a single atomic site and they are hybridized with valence or conduction electron states. The effect of a core-hole potential in the final state of CLS plays an important role. Typical examples of calculated results for XPS in rare-earth compounds and transition metal compounds are given. Recent developments in the study of resonant X-ray emission spectra (RXES) are also introduced. A theoretical approach beyond the IAM is discussed mainly for the analysis of RXES of transition metal compounds.     

Using X(3823)→J/ψπ+π− to identify coupled-channel effects

Very recently, the Belle and BESIII experiments observed a new charmonium-like state X(3823), which is a good candidate for the D-wave charmonium ψ(1³D₂). Because the X(3823) is just near the D ¯D^∗ threshold, the decay X(3823)→ J/ψπ⁺π⁻ can be a golden channel to test the significance of coupled-channel effects. In this work, this decay is considered including both the hidden-charm dipion and the usual quantum chromodynamics multipole expansion (QCDME) contributions. The partial decay width, the dipion invariant mass spectrum distribution dΓ[X(3823) → J/ψπ⁺π⁻]/dm_π⁺_π⁻, and the corresponding dΓ[X(3823) → J/ψπ⁺π⁻]/d cos θ distribution are computed. Many parameters are determined from existing experimental data, so the results depend mainly only on one unknown phase between the QCDME and hidden-charm dipion amplitudes.     

X-ray excited KLL and KLM Auger spectra of manganese

High resolution (ΔE < 1.5 eV) manganese KLL and KLM Auger spectra, obtained by photoexcitation, are persented, and the transition energies and intensities are compared with the experimental and theoretical data published earlier. Significant disagreement can be observed between the respective experimental intensity values in the cases of the most intense lines, and large differences are found between the experimental and the available theoretical transition energy values of the main peaks. The disagreements between the experimental data can be explained rather by the different chemical states of the manganese samples investigated in the separate experiments than by the different mechanisms of the Auger processes.     

O KVV Auger emission versus resonant photoemission at the O K edge of high-Tc superconductors

Photoelectron spectroscopy results on single crystals of the superconductors Bi₂Sr₂CaCu₂O₈,Bi₂Sr₂CuO₆, Ba_0.6K_0.4BiO₃ and the semiconductor Ba_0.9K_0.1BiO₃ are reported for the photon energy region around the O K absorption threshold. The development of the O-KVV Auger structure has been carefully monitored as a function of photon energy. A non-monotonic behavior displaying a feature at a constant binding energy of about 14 eV was found for Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂CuO₆ in a narrow photon energy region of 1 eV at the main edge of the O K absorption spectrum around 530 eV. The corresponding enhancement, connected with the autoionization of O 2p states, is absent in Ba_1−xK_xBiO ₃ in contrast to Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂CuO₆. The resonant enhancement is more pronounced for Bi₂Sr₂CuO₆ as compared to Bi₂Sr₂CaCu₂O₈, which can be explained by a lower charge carrier concentration in the former case, leading to a more localized nature of intermediate O 2p states. The model parameters Cu d–d and O p–p Coulomb interactions and the charge transfer energy Δ are estimated from the experiments.     

Quasi-SU(3) truncation scheme for even–even sd-shell nuclei

The quasi-SU(3) symmetry was uncovered in full pf and sdg shell-model calculations for both even–even and odd–even nuclei. It manifests itself through a dominance of single-particle and quadrupole–quadrupole terms in a Hamiltonian used to describe well-deformed nuclei. A practical consequence of the quasi-SU(3) symmetry is an efficient basis truncation scheme. In [C.E. Vargas et al., Phys. Rev. C 58 (1998) 1488] it is shown that when this type of Hamiltonian is diagonalized in an SU(3) basis, only a few irreducible representations (irreps) of SU(3) are needed to describe the yrast band, the leading S=0 irrep augmented with the leading S=1 irreps in the proton and neutron subspaces. In the present article the quasi-SU(3) truncation scheme is used, in conjunction with a “realistic but schematic” Hamiltonian that includes the most important multipole terms, to describe the energy spectra and B(E2) transition strengths of ^20,22Ne, ²⁴Mg and ²⁸Si. The effect of the size of the Hilbert space on both sets of observables is discussed, as well as the structure of the yrast band and the importance of the various terms in the Hamiltonian. The limitations of the model are explicitly discussed.     

N00N态的Wigner函数及N00N态作为输入的量子干涉

根据量子力学相干态表象下的Wigner函数公式, 推导了N00N态在相空间的Wigner分布函数的解析表达式. 基于相空间方法, 研究N00N态作为输入的量子干涉. 推导了与输入光场参数和干涉仪参数相关的输出端探测光子概率的解析表达式, 并进行了数值分析. 从分析结果发现, 当相移参数φ取0和π时, 输出量子态仍为N00N态. 当输入2002态时, 输出结果总是2002态, 与相移参数无关. 随着N的增加, 条件概率随相位的分布峰数一般只有一个, 两个, 三个或四个, 且峰变得更窄. 这些结果可以为实验提供理论指导. 关键词： N00N态 Wigner函数 相空间 量子干涉     

万有引力常数G精确测量实验进展

万有引力常数G是人类历史上引入的第一个基本物理学常数,其在理论物理、天体物理和地球物理等许多领域中扮演着重要角色.两百多年来,人们共测量出了200多个G值,但G的测量精度仍然是所有物理学常数中最差的,这一现象反映了测G工作本身的复杂性和困难性.本文简要概述了G值测量的意义和测G的历史,并结合自2010年以来国际上新出现的三个高精度测G实验介绍这一领域的研究进展,以及华中科技大学引力实验中心测G工作的最新动态.     

Hyperon-Nucleon bound states and electroproduction of strangeness on He

The A(e, e′K⁺)YX reaction has been investigated in Hall C at Jefferson Lab. Data were taken for Q² ≈ 0.35 and 0.5 GeV² at a beam energy of 3.245 GeV for ³He, ⁴He. The missing mass spectra are fitted with Monte Carlo simulations including Λ, Σ⁰, Σ⁻ hyperon production. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Λ-hypernuclear bound states is seen for ^3,4He targets.     

Anisotropic percolation and the d-dimensional surface roughening problem

We review recent numerical simulations of several models of interface growth in d-dimensional media with quenched disorder. These models belong to the universality class of anisotropic diode-resistor percolation networks. The values of the roughness exponent δ=0.63±0.01 (d=1+1) and δ=0.48±0.02 (d=2+1) are in good agreement with our recent experiments. The values of δ in higher dimensions (δ=0.38±0.03 in d=4 and δ=0.27±0.05 in d=5) do not support a recent theoretical conjecture.     

K(m,n,P)方程多-Compacton相互作用的数值研究

采用有限差分法对非线性色散K(m,n,p)方程的多-Compacton之间的相互作用进行了数值研究.该差分方法为二阶精度且线性意义下绝对稳定的无耗散格式,通过添加人工耗散项有效防止了数值解的爆破现象.首先对单-Compacton的长时间演化行为进行了数值模拟,验证了数值方法的有效性.然后对双-CompaCton和三-Compacton的碰撞过程进行了数值研究,发现多-Compacton碰撞之后基本保持碰撞之前的波形和波速,但在波后产生小振幅的Compacton-Anticompacton对.     

一维扩展t-J模型中密度-自旋相互作用诱导的相分离

t-J模型是研究高温超导电性的重要理论模型之一. 最近的冷分子实验表明可用极性分子模拟t-J模型. 实验模拟的t-J模型除了引进长程的偶极相互作用外, 还引进了密度-自旋相互作用. 本文使用密度矩阵重整化群方法研究了密度-自旋相互作用对一维t-J 模型基态性质的影响. 选取了t-J模型基态相图中不同相区的三个点, 计算了不同密度-自旋相互作用强度下的粒子数和自旋的实空间分布,以及密度-密度关联函数和自旋-自旋关联函数与相应的结构因子. 计算结果表明, 密度-自旋相互作用强度较弱时, 对系统的性质不会产生定性影响;当其强度足够大时, 系统会进入相分离, 该相分离与传统t-J模型的相分离有很大区别.     

Solid-state electrochemical CO2 sensor by coupling lithium ion conductor (Li2CO3-Li3PO4-Asl2O3) with oxide ion-electron mixed conductor (La0.9Sr0.1MnO3)

A solid-state electrochemical cell of the type O₂(air), PtLa_0.9Sr_0.1MnO₃/Li₂CO₃(+5 mol% Li₃PO₄ + 6 mol% Al₂O₃)/Au, CO₂, O₂ was composed to determine CO₂ concentration, where Li₂CO₃, a lithium ion conductor, was used as an electrolyte, and the perovskite-type oxide (La_0.9Sr_0.1MnO₃)/O₂-electrode as a reference electrode. The electromotive force (EMF) of the cell was found to be proportional to the logarithm of CO/₂ partial pressure in CO₂/O₂/N₂ gas mixtures at temperatures between 300 and 400 °C. The EMF responded to changes of CO₂ partial pressure within 1 min at 400 °C. The sensitivity to CO₂ of this cell was not affected by coexistence of O₂, and the EMF remained constant after the first 15 days. The mechanism for sensing CO₂ is discussed.     

大规模宽频弹性动力学分析的快速定向压缩边界元法

发展一种大规模宽频弹性动力学分析的快速定向压缩边界元法.证明弹性动力学核函数具有定向低秩特性，为采用快速定向压缩算法提供理论基础.根据S波的波数，将节点之间的相互作用划分为低频相互作用和高频相互作用，并将后者进一步划分为与多个楔形区.在楔形区上，可以采用核函数的定向低秩特性进行快速计算.低频相互作用与核无关快速多极边界元法中计算方法相同，不同方向楔形区上的变换矩阵可以采用坐标系旋转的方法进行快速计算.可对任意频率进行快速谐响应分析.数值算例表明：该方法可以将宽频弹性动力学问题计算复杂度降低到O（N log^αN）.与卷积求积边界元法相结合，也可以应用于弹性动力学瞬态分析.     

Absorption cross sections for antiprotons on carbon, aluminum and copper at 485 and 597 MeV/c

Absorption cross sections for antiprotons on C, Al and Cu have been measured by a transmission method at 485 and 597 MeV/c. Nuclei are shown to be black to antiprotons at these momenta. Using the available data up to 280 GeV/c, the momentum dependence of the absorption cross sections is investigated. Empirically, a simple expression σ_abs = γ(p/p₀)^−β, with β and γ constants and p₀ = 1 GeV/c, gives a good account of the data in a remarkably wide momentum range, 0.5–280 GeV/c.     

The O(N) vector model in the large-N limit revisited: multicritical points and double scaling limit

The multicritical points of the O(N)-invariant N vector model in the large-N limit are re-examined. Of particular interest are the subtleties involved in the stability of the phase structure at critical dimensions. In the limit N → ∞ while the coupling g → g_c in a correlated manner (the double scaling limit) a massless bound state O(N) singlet is formed and powers of 1/N are compensated by IR singularities. The persistence of the N → ∞ results beyond the leading order is then studied with particular interest in the possible existence of a phase with propagating small mass vector fields and a massless singlet bound state. We point out that under certain conditions the double scaled theory of the singlet field is non-interacting in critical dimensions.     

Minimal SUSY SO(10), b–τ unification and large neutrino mixings

We show that the assumption of type II seesaw mechanism for small neutrino masses coupled with b–τ mass unification in a minimal SUSY SO(10) model leads not only to a natural understanding of large atmospheric mixing angle (θ₂₃) among neutrinos, as recently noted, but also to large solar angle (θ₁₂) and a small θ₁₃≡U_e3 as required to fit observations. No additional symmetries are required to obtain large neutrino mixings. The proposed long baseline neutrino experiments will provide a crucial test of this model since it predicts U_e30.16.     

Local magnetic moment in the two-dimensional reduced p-d model

A two-dimensional reduced p-d model describing CuO₂ sheets in high-T_c oxides is studied by use of the composite operator approach. A set of self-consistent equations for the Green function is derived in a generalized mean-field approximation for the paramagnetic state. The results show a good agreement with the exact results obtained by numerical simulations on finite size lattices.     

The angular momentum and parity projected multidimensionally constrained relativistic Hartree–Bogoliubov model

Nuclear deformations are fundamentally important in nuclear physics.We recently developed a multidimensionally constrained relativistic Hartree-Bogoliubov(MDCRHB)model,in which all multipole deformations respecting the V₄ symmetry can be considered self-consistently.In this work we extend this model by incorporating the angular momentum projection and parity projection to restore the rotational and parity symmetries broken in the mean-field level.This projected MDCRHB(p-MDCRHB)model enables us to connect certain nuclear spectra to exotic intrinsic shapes such as triangles or tetrahedrons.We present the details of the method and an exemplary calculation for ¹²C.We develop a triangular moment constraint to generate the triangular configurations consisting of three α clusters arranged as an equilateral triangle.The resulting ¹²C spectra are consistent with that from a triangular rigid rotor for large separations between the α clusters.We also calculate the B(E2)and B(E3)values for low-lying states and find good agreement with the experiments.     

Dynamics of O(N) chiral supersymmetry at finite energy density

We consider an O(N) version of a massive, interacting, chiral supersymmetry model solved exactly in the large N limit. We demonstrate that the system approaches a stable attractor at high energy densities, corresponding to a non-perturbative state for which the relevant field quanta are massless. The state is one of spontaneously broken O(N), which, due to the influence of supersymmetry, does not become restored at high energies. Introducing soft supersymmetry breaking to the Lagrangian results in scalar masses at the soft breaking scale m_s independent of the mass scale of supersymmetry μ, with even smaller masses for the fermions.