Process <Emphasis Type="Italic">γ</Emphasis>*<Emphasis Type="Italic">γ</Emphasis> → <Emphasis Type="Italic">σ</Emphasis> at large virtuality of <Emphasis Type="Italic">γ</Emphasis>*

The process γ*γ → σ is investigated in the framework of the SU(2)×SU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of γ* in the Euclidean kinematic domain. The asymptotic behavior of this form factor resembles the asymptotic behavior of the γ*γ → π form factor.     

Mössbauer studies of multiferroics BiFe<Subscript>1 – <Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0–0.20)

The Mössbauer studies on ⁵⁷Fe nuclei in multiferroics BiFe_{1 – x} Cr _x O₃ (x = 0.05, 0.10, and 0.20) have been performed at room temperature. The multiferroics BiFe_{1 – x} Cr _x O₃ (x = 0.05, 0.10, and 0.20) with the rhombohedral R3c structure have been prepared by solid-state synthesis under high pressures. The effect of substitution of Cr cations for Fe cations on the spatial spin-modulated structure, and also hyperfine electrical and magnetic interactions of ⁵⁷Fe nuclei has been studied. The substituted ferrites demonstrate an anharmonic modulated spin structure of cycloid type, in which iron atoms with different cation environments take part. The anharmonism parameter of the cycloid linearly increases from m = 0.10 at x = 0 to m = 0.78 ± 0.02 at x = 0.20. The constants of magnetic uniaxial anisotropy K _u are estimated at room temperature: K _u ≈ 0.36 × 10⁶ erg/cm³ at x = 0 and K _u ≈ 4.22 × 10⁶ erg/cm³ at x = 0.20.     

Higher <Emphasis Type="Italic">η</Emphasis><Subscript>c</Subscript>(<Emphasis Type="Italic">nS</Emphasis>) and <Emphasis Type="Italic">η</Emphasis><Subscript>b</Subscript>(<Emphasis Type="Italic">nS</Emphasis>) mesons

The hyperfine splittings in heavy quarkonia are studied in a model-independent way using experimental data on dielectron widths. Relativistic correlations are taken into account together with the smearing of spin-spin interaction. The radius of smearing is fixed by known G/ψ−η _c(1S), ψ(2S)−η _c′(2S) splittings, which appears to be small, r _ss ≅ 0.06 fm. Nevertheless, even with such a small radius, substantial suppression of hyperfine splittings (∼50%) is observed in bottomonium. For nS b states (n = 1, 2, ..., 6), our predicted splittings (in MeV) are 28, 12, 10, 5, 6, 3. For the 3S and 4S charmonium states, the splittings 16(2) and 12(4) MeV are obtained. The text was submitted by the authors in English.     

High-temperature study of SrFe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mo<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3−<Emphasis Type="Italic">z</Emphasis></Subscript> perovskites

The structure of high-temperature SrFe_{1 − x} Mo _x O_{3 − z} (0 ≤ x ≤ 0.5) phases was studied. Such studies are necessary to understand the mechanism of oxygen transport in membrane materials used for high-temperature oxygen separation.     

X-ray,Mössbauer,and magnetic research of system Y(Fe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript> alloys

The structural transformations and magnetic phase transitions in the quasibinary system Y(Fe_{1 ? x} Al _x )₂ have been investigated by Mössbauer spectroscopy, X-ray diffractometry, and magnetic measurements of polycrystals.     

Inclusive <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> photoproduction and polarization at HERA in the <Emphasis Type="Italic">k</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>-factorization approach

We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the k _T -factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics.     

Thermal and magnetic properties of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript>

The thermodynamic and magnetic properties of the La_{1 − x} Pb _x MnO₃ (0.24 ≤ x ≤ 0.40) solid solution system were investigated in the temperature range of 4.2–340 K. All objects were ferromagnetics with Curie temperature T _C ≈ 320–340 K, which slowly increased with x. The M(T) behavior in the magnetic ordering region indicated a nonuniform ground state, due possibly to the competition of ferromagnetic and antiferromagnetic interactions. The increase in the saturation magnetic moment with x can be described by a simple model of the binary bonds in La_{1 − x} Pb _x MnO₃.     

X-Ray Diffraction and Mössbauer Studies of the Structural Features of BiFe<Subscript>1 ‒ <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> Multiferroics

The structure of ceramic BiFe_1?xZn_xO₃ multiferroic samples is investigated using the X-ray diffraction method and Mössbauer spectroscopy. X-ray diffraction analysis of the samples indicates the existence of the Bi₁₂(Bi_0.5Fe_0.5)O_19.5 impurity phase. High-temperature heating of the samples generates additional phases. The parameters of the Mössbauer spectra depend on the zinc concentration. In this case, for pure bismuth ferrite, the spectrum is a superposition between two Zeeman sextets and two paramagnetic doublets arising from two nonequivalent magnetic and electrical positions occupied by iron ions at the crystallattice sites of a sample. The replacement of iron ions with zinc ions substantially affects the spectrum parameters. This is probably related to changes in the spin-cycloid structure typical of multiferroics, the destruction of which stimulates the appearance of significant magnetoelectric interactions.     

Search for <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript> → µµ<Emphasis Type="Italic">γ</Emphasis> at large hadron collider

The branching ratio for B _s → ℓ⁺ℓ⁻ γ mode is of the same order as B _s → ℓ⁺ℓ⁻, since there is no helicity suppression in the 3-body decay mode. New Physics beyond Standard Model may affect these rates favourably for experimental observation at LHC and simultaneous measurements of the modes B _s → μ⁺μ⁻ and B _s → μ⁺μ⁻ γ at LHC experiment will indicate the basic nature of the interaction at play. A simulation study has been performed to evaluate the potential of CMS detector to observe the more difficult mode of B _s → μ⁺μ⁻γ. An upper limit of 2.08 × 10⁻⁷ on the branching ratio is expected to be achieved corresponding to an integrated luminosity of 10 fb⁻¹.     

Magnetic and Mössbauer study of ε-Fe<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>N (2 < <Emphasis Type="Italic">y</Emphasis> < 3) nanoparticles

ε-Fe _y N (2 < y < 3) nanoparticles were prepared by the nitridation of spindle type hematite nanoparticles using ammonia at a temperature of 550 °C. Chemical analysis for the elements brings out the composition as y = 2.56. These nanoparticles show ferromagnetic behaviour even though it has higher nitrogen content than the stoichiometric Fe₃N. The quenching of the particles from higher temperature and the higher nitrogen content introduces disorder in the system unlike the ordered ε-Fe₃N. Mössbauer spectroscopy at lower temperature clearly shows the existence of two sextets corresponds to the two types of iron environments. The presence of more than one site excludes perfect ordering. This is consistent with the peak widths which result from variations in the distributions of next nearest interstitial neighbours. Existence of two different Debye temperatures for two iron sites shows that it varies according to the number and type of neighbouring atoms.     

Template-free synthesis of hollow <Emphasis Type="Italic">α</Emphasis>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> microspheres

Nearly monodisperse hollow α-Fe₂O₃ microspheres composed of nanoparticles have been successfully synthesized through a facile template-free hydrothermal method. The products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It is shown that the hollow α-Fe₂O₃ microspheres consist of well-aligned α-Fe₂O₃ nanoparticles with a mean diameter of about 15 nm. This facile reaction route presents an efficient method for mass production of monodisperse hollow magnetic nanomaterials. The final α-Fe₂O₃ microspheres exhibit special magnetic properties with a small remnant magnetization of 0.09 emu g⁻¹ and a high coercivity of 1121.67 Oe at room temperature.     

<Emphasis Type="Italic">θ</Emphasis><Subscript>13</Subscript> measurements at accelerators

The θ₁₃ mixing angle measurements in the neutrino oscillation experiments at accelerators are presented with the perspectives for futures of neutrino beam facilities. Particular emphasis is devoted to near-term new neutrino beam options, such low energy beams and the off-axis technique.     

Long-range magnetic order in Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Na<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>2</Subscript>O<Subscript>2</Subscript>

Single crystals of Li _x Na_{1 ? x} Cu₂O₂ solid solutions have been grown from the melt and crystal lattice parameters have been studied. It is found that the solid solution of this system exists in the region x ≤ 0.25. Specific heat and magnetic susceptibility are investigated on monocrystalline samples with x = 0.07, 0.14, and 0.21. Long-range magnetic order in these compounds is formed at T = 13.8, 4.1, and 14.8 K, respectively. It is found that the Néel temperature T _N in these compounds increases with Li content.     

Ordered phases of lithium nickelite Li<Subscript>1−<Emphasis Type="Italic">x</Emphasis>−<Emphasis Type="Italic">z</Emphasis></Subscript>Ni<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

A symmetry analysis of ordering in lithium nickelite Li_1?x?zNi_1+xO₂ (Li_1?x?z□_yNi_1+xO₂) was performed with regard to the substitution of Li and Ni atoms and the occurrence of structural vacancies □ in the metal sublattice. For all the ordered phases, the k ₉ ⁽³⁾ ray of the Lifshitz {k₉} star is present in the order-disorder transition channel. This ray determines the consecutive alternation of atomic planes filled with only Ni atoms or only Li atoms and vacancies in the \([1\bar 11]_{B1} \) direction. It was shown that the rhombohedral ordered LiNiO₂ phase is formed in the defect-free lithium nickelite, whereas a family of three monoclinic Li₃□Ni₄O₈ (C2/m space group) and Li₂□Ni₃O₆ (C2/m and C2 space groups) superstructures arises as the concentration of structural vacancies increases. For all the superstructures, the order-disorder phase-transition channels were determined and the distribution functions of Li and Ni atoms have been calculated. The long-range order parameters describing each superstructure were found as functions of the Li_{1?x? z}Ni_1+xO₂ composition.     

<Emphasis Type="Italic">Om</Emphasis> Diagnostic for Two-Parameter <Emphasis Type="Italic">ω</Emphasis><Subscript><Emphasis Type="Italic">σ</Emphasis></Subscript> in Dilaton Dark Energy

Om diagnostic is a good geometric method to differentiate one dark energy model from LCDM. We apply three different two-parameter equation of state ω _σ (EOS) to Dilaton Dark energy (DDE) model and investigate the Om diagnostic for these cases. We obtain that DDE model can be easily distinguished from LCDM no matter which case is considered. We also investigate the influence of coupled parameter α on the evolutive behavior of Om−z. According to the numerical result of Om, we get the current value of equation of state ω _σ0=−0.939 which fits the observational data well.     

The cusp effect in <Emphasis Type="Italic">η</Emphasis>′→<Emphasis Type="Italic">η</Emphasis><Emphasis Type="Italic">π</Emphasis><Emphasis Type="Italic">π</Emphasis> decays

Strong final-state interactions create a pronounced cusp in η′→η π ⁰ π ⁰ decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of π π scattering lengths from K→3π decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the π ⁺ π ⁻ threshold.     

Quark spectral properties above <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> from Dyson–Schwinger equations

We report on an analysis of the quark spectral representation at finite temperatures based on the quark propagator determined from its Dyson–Schwinger equation in Landau gauge. In Euclidean space we achieve nice agreement with recent results from quenched lattice QCD. We find different analytical properties of the quark propagator below and above the deconfinement transition. Using a variety of ansätze for the spectral function we then analyze the possible quasiparticle spectrum, in particular its quark mass and momentum dependence in the high temperature phase. This analysis is completed by an application of the Maximum Entropy Method, in principle allowing for any positive semi-definite spectral function. Our results motivate a more direct determination of the spectral function in the framework of Dyson–Schwinger equations.     

The magnetic properties of nanosized La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> (0.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.8)

Magnetic properties of La_1−x Ca _x MnO₃ (0.5 ≤ x ≤ 0.8) samples with an equivalent average particle size ~50 nm prepared by a sol–gel method were investigated. The charge ordering (CO) transition that is observed in the bulks disappears and the ferromagnetic (FM) transition occurs in all the prepared samples. For all the samples, the spontaneous magnetization (M _S) value is much lower than the corresponding theoretic value, which shows that the majority of the sample is antiferromagnetic (AFM). However, the M _S value is much larger than the corresponding value reported by some other groups. The invisible of CO transition and the large M _S value can be attributed to the good connection among the adjacent particles. Moreover, the exchange bias (EB) phenomenon is observed except the x = 0.5 sample. With x increasing, the M _S value decreases and the EB field increases, which can be understood by considering the coexistence of FM phase with Mn³⁺–Mn⁴⁺ spin clusters in the shell and the AFM phase in the core of the nanoparticles.     

Magnetic property and Mössbauer analysis of SrSn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Bold">x</Emphasis></Subscript>O<Subscript>3</Subscript> prepared by a sol-gel method

The dilute magnetic properties of SrSn_1?xFe_xO₃ (x = 0.01 ? 0.15) prepared by sol-gel and thermal decomposition methods were investigated by ⁵⁷Fe Mössbauer spectrometry, magnetometry, and X-ray diffractometry. It was found that SrSnO₃ doped with 2–8 % Fe show weak ferromagnetism although only paramagnetic doublets are observed in ⁵⁷Fe Mössbauer spectra at room temperature (RT), whereas SrSnO₃ doped with 10–15 % Fe show relatively strong ferromagnetism, and the sextets are additionally observed in the ⁵⁷Fe Mössbauer spectra at RT. The weak ferromagnetism by doping 2–8 % Fe is considered to be caused by the induced magnetic defects, and the ferromagnetism by doping 10–15 % Fe are considered mainly due to the magnetic coupling between dilute Fe ³⁺ partially substituted at Sn ⁴⁺ sites in the orthorhombic structure of SrSnO_3?δ accompanying the oxygen deficiencies. It is further remarkable that poor crystalline 8 % Fe doped SrSnO_3?δ obtained by annealing at 600 ^°C shows relatively high saturation magnetization and low coercivity.