Output characteristics of mixed holograms in the ($$\left( {\overline {11} 0} \right)$$)-Cut Bi12TiO20 crystal

An analytical solution to the system of linear differential equations that describe the reconstruction of object wave using a transmission holographic grating formed in a cubic photorefractive piezoelectric (\(\left( {\overline {11} 0} \right)\))- cut crystal with the 23 symmetry is derived. The solution is used to interpret the experimental results on the dependence of the diffraction efficiency of mixed holograms on the thickness of the Bi₁₂TiO₂₀ crystal at a fixed orientation angle and three azimuths of linear polarization of the readout reference beam. The best agreement of the theoretical and experimental results on mixed holograms is reached when the inverse piezoelectric effect and photoelasticity are taken into account in addition to the conventional electrooptic effect.     

Polarization-optical and X-ray diffraction investigations on the symmetry of distorted phases of ammonium cryolite (NH4)3 ScF6

Single-crystal plates of different sections of the (NH₄)₃ScF₆ crystal have been investigated by polarization-optical microscopy and X-ray diffraction over a wide temperature range, including the temperatures of two known phase transitions and the third transition found recently. It is established that the symmetry of 5 phases changes in the following sequence: $\begin{gathered} O_h^5 - Fm3m(Z = 4) \leftrightarrow C_{2h}^5 - {{P12_1 } \mathord{\left/ {\vphantom {{P12_1 } {n1}}} \right. \kern-0em} {n1}}(Z = 2) \leftrightarrow C_{2h}^3 - {{I12} \mathord{\left/ {\vphantom {{I12} {m1}}} \right. \kern-0em} {m1}} \\ (Z = 16) \leftrightarrow C_i^1 - I\bar 1(Z = 16) \\ \end{gathered} $ .     

Investigation of creep in Ni3Ge alloy single crystals oriented along axes \left[ {\bar 234} \right] and \left[ {\bar 122} \right]

The creep of Ni₃Ge alloy single crystals is investigated at temperatures of 873, 923, and 973 K, which lie above the temperature of the anomalous peak behavior of mechanical properties with the deformation axis orientations $\left[ {\bar 234} \right]$ and $\left[ {\bar 122} \right]$ for which cubic slip is characteristic. It is shown that the steady state creep rate depends weakly on temperature.     

Magnetic, thermal and hyperfine behaviours of Tm3+ in TmPO4, YPO4 and LuPO4: a comparative study

Single crystals of thulium phosphates (TmPO₄) are grown and the principal magnetic susceptibility perpendicular to the symmetry axis ‘c’ of the crystal $$\left( {{\text{ $ \chi $ }}_ \bot } \right)$$ and the magnetic anisotropy $$\Delta {\text{ $ \chi $ }}\left( {{\text{ = $ \chi $ }}_\parallel - {\text{ $ \chi $ }}_ \bot } \right)$$ are measured in the temperature range 300–13.5 K and 300–80 K, respectively. Though $${\text{ $ \chi $ }}_ \bot $$ increases rapidly with the decrease of temperature, $${\text{ $ \chi $ }}_\parallel $$ increases very slowly with the lowering of temperature. The tetragonal crystal structure of TmPO₄ is similar to that of Tm³⁺ in YPO₄ and LuPO₄ and in all the cases the non-Kramers Tm³⁺ ion occupies a site of D_2d symmetry. Our observed magnetic data on TmPO₄ are analyzed using crystal field analysis where the Hamiltonian includes the atomic free ion and crystal field (one-electron) interaction term. The computed and measured paramagnetic susceptibilities of TmPO₄ agree very well in the temperature range of our study. The magnetic behaviours of Tm³⁺ in YPO₄ and LuPO₄ are also studied and the results are compared with that of TmPO₄. In all the cases the natures of thermal variations of average susceptibilities and magnetic anisotropies are mostly governed by the perpendicular susceptibilities as their values are higher and rapidly increase with the lowering of temperature compared to parallel susceptibilities. The computed nuclear quadruple splittings, electronic heat capacities of Tm³⁺ in three different hosts give some interesting results.     

Topological vertex,string amplitudes and spectral functions of hyperbolic geometry

We study radiative corrections to massless quantum electrodynamics modified by two dimension-five LV interactions $\bar{\Psi } \gamma ^{\mu } b'^{\nu } F_{\mu \nu }\Psi $ and $\bar{\Psi }\gamma ^{\mu }b^{\nu } \tilde{F}_{\mu \nu } \Psi $ in the framework of effective field theories. All divergent one-particle-irreducible Feynman diagrams are calculated at one-loop order and several related issues are discussed. It is found that massless quantum electrodynamics modified by the interaction $\bar{\Psi } \gamma ^{\mu } b'^{\nu } F_{\mu \nu }\Psi $ alone is one-loop renormalizable and the result can be understood on the grounds of symmetry. In this context the one-loop Lorentz-violating beta function is derived and the corresponding running coefficients are obtained.     

Calculations of the Spin-Hamiltonian Parameters for the Trigonal Cr3+ and Mn4+ Centers in Ca3Ga2Ge3O12 (CGGG) Garnet Crystal

The spin-Hamiltonian parameters (zero-field splitting D, g-factors g _//, g _⊥ and hyperfine structure constants A _//, A _⊥) of Cr³⁺ and Mn⁴⁺ ions at the trigonal Ga³⁺ site of Ca₃Ga₂Ge₃O₁₂ (CGGG) garnet crystals are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, besides the contributions to spin-Hamiltonian parameters from the crystal-field (CF) mechanism in the frequently applied CF theory, those from the charge-transfer (CT) mechanism (which is neglected in CF theory) are taken into account. The calculated results are in reasonable agreement with the experimental values. The defect structures of Cr³⁺ and Mn⁴⁺ impurity centers in CGGG crystals are also obtained from the calculations. The calculations show that the relative importance of CF mechanism (characterized by $ \left| {{{Q^{\text{CT}} } \mathord{\left/ {\vphantom {{Q^{\text{CT}} } {Q^{\text{CF}} }}} \right. \kern-0pt} {Q^{\text{CF}} }}} \right| $ , where $ Q = D,\;\Delta g_{\rm{//}} ,\;\Delta g_{ \bot } ,\;A_{\rm{//}}^{(2)} or\;A_{ \bot }^{(2)} $ ) for Mn⁴⁺ center in CGGG is larger than that for Cr³⁺ center. So, for the high valence state dⁿ ions in crystals, the reasonable calculations of spin-Hamiltonian parameters should consider the contributions due to both the CF and CT mechanisms.     

Physics beyond the Standard Model through b → s μ ?+? μ ? transition

A comprehensive study of the impact of new-physics operators with different Lorentz structures on decays involving the b ?? s ?? ^?+? ?? ^? transition is performed. The effects of new vector?Caxial vector (VA), scalar?Cpseudoscalar (SP) and tensor (T) interactions on the differential branching ratios, forward?Cbackward asymmetries (A _FB??s), and direct CP asymmetries of ${\bar B}_{\rm s}^0 \to \mu^+ \mu^-$ , ${\bar B}_{\rm d}^0 \to$ $ X_{\rm s} \mu^+ \mu^-$ , ${\bar B}_{\rm s}^0 \to \mu^+ \mu^- \gamma$ , ${\bar B}_{\rm d}^0 \to {\bar K} \mu^+ \mu^-$ , and ${\bar B}_{\rm d}^0\to {\bar{K}^*} \mu^+ \mu^-$ are examined. In ${\bar B}_{\rm d}^0\to {\bar{K}^*} \mu^+ \mu^-$ , we also explore the longitudinal polarization fraction f _L and the angular asymmetries $A_{\rm T}^{(2)}$ and A _LT, the direct CP asymmetries in them, as well as the triple-product CP asymmetries $A_{\rm T}^{\rm (im)}$ and $A^{\rm (im)}_{\rm LT}$ . While the new VA operators can significantly enhance most of the observables beyond the Standard Model predictions, the SP and T operators can do this only for A _FB in ${\bar B}_{\rm d}^0 \to {\bar K} \mu^+ \mu^-$ .     

Alternative technique for Standard Model estimation of the rare kaon decay branchings \left. {BR(K \to \pi \nu \bar \nu )} \right|_{SM}

We estimate $BR(K \to \pi \nu \bar \nu )$ in the context of the Standard Model by fitting for λ _t≡V _tdV _ts ^* of the “kaon unitarity triangle” relation. To find the vertex of this triangle, we fit data from |? _K|, the CP-violating parameter describing K mixing, and a _ψ,K , the CP-violating asymmetry in B _d ⁰ → J/ψK ⁰ decays, and obtain the values $\left. {BR(K \to \pi \nu \bar \nu )} \right|_{SM} = (7.07 \pm 1.03) \times 10^{ - 11} $ and $\left. {BR(K_L^0 \to \pi ^0 \nu \bar \nu )} \right|_{SM} = (2.60 \pm 0.52) \times 10^{ - 11} $ . Our estimate is independent of the CKM matrix element V _cb and of the ratio of B-mixing frequencies ${{\Delta m_{B_s } } \mathord{\left/ {\vphantom {{\Delta m_{B_s } } {\Delta m_{B_d } }}} \right. \kern-0em} {\Delta m_{B_d } }}$ . We also use the constraint estimation of λ _t with additional data from $\Delta m_{B_d } $ and |V _ub|. This combined analysis slightly increases the precision of the rate estimation of $K^ + \to \pi ^ + \nu \bar \nu $ and $K_L^0 \to \pi ^0 \nu \bar \nu $ (by ?10 and ?20%, respectively). The measured value of $BR(K^ + \to \pi ^ + \nu \bar \nu )$ can be compared both to this estimate and to predictions made from ${{\Delta m_{B_s } } \mathord{\left/ {\vphantom {{\Delta m_{B_s } } {\Delta m_{B_d } }}} \right. \kern-0em} {\Delta m_{B_d } }}$ .     

Absorption of solar radiation by solar neutrinos

We calculate the absorption probability of photons radiated from the surface of the Sun by a left-handed neutrino with definite mass and a typical momentum for which we choose |p₁| = 0.2 MeV, producing a heavier right-handed antineutrino. Considering the two transitions and we obtain the two oscillation lengths L₁₂ = 4960.8 m, L₂₃ = 198.4 m, the two absorption probabilities P₁₂^abs. = 2.5 x 10^-67, P₂₃^abs. = 1.2 x 10^-58 and the two absorption ranges au, au, using a neutrino mass differences of meV, meV and associated transition dipole moments. We collect all necessary theoretical ingredients, i.e. neutrino mass and mixing scheme, induced electromagnetic transition dipole moments, quadratic charged lepton mass asymmetries and their interdependence.Received: 4 November 2003, Revised: 23 March 2004, Published online: 5 May 2004     

Cosmological perturbations in SFT inspired non-local scalar field models

We clearly and consistently supersymmetrize the celebrated horizontality condition to derive the off-shell nilpotent and absolutely anticommuting Becchi?CRouet?CStora?CTyutin (BRST) and anti-BRST symmetry transformations for the supersymmetric system of a free spinning relativistic particle within the framework of superfield approach to BRST formalism. For the precise determination of the proper (anti-)BRST symmetry transformations for all the bosonic and fermionic dynamical variables of our system, we consider the present theory on a (1,2)-dimensional supermanifold parameterized by an even (bosonic) variable (??) and a pair of odd (fermionic) variables ?? and $\bar{\theta}$ (with $\theta^{2} = \bar{\theta}^{2} = 0$ , $\theta\bar{\theta}+ \bar{\theta}\theta= 0$ ) of the Grassmann algebra. One of the most important and novel features of our present investigation is the derivation of (anti-)BRST invariant Curci?CFerrari type restriction which turns out to be responsible for the absolute anticommutativity of the (anti-)BRST transformations and existence of the coupled (but equivalent) Lagrangians for the present theory of a supersymmetric system. These observations are completely new results for this model.     

Charm Production in Antiproton-Proton Annihilation

We study the production of charmed mesons (D) and baryons (?? _c ) in antiproton-proton ${(\bar{p}p)}$ annihilation close to their respective production thresholds. The elementary charm production process is described by either baryon/meson exchange or by quark/gluon dynamics. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on ${\bar{p}p \to \bar{\Lambda} \Lambda}$ and ${\bar{p} p \to \bar{K} K}$ by connecting the processes via SU(4) flavor symmetry. Our predictions for the ${\bar{\Lambda}_c \Lambda_c}$ production cross section are in the order of 1 to 7 mb, i.e. a factor of around 10?C70 smaller than the corresponding cross sections for ${\bar{\Lambda} \Lambda}$ However, they are 100 to 1000 times larger than predictions of other model calculations in the literature. On the other hand, the resulting cross sections for ${\bar{D} D}$ production are found to be in the order of 10^?2 ?C 10^?1 ??b and they turned out to be comparable to those obtained in other studies.     

Coupling constant in dispersive model

The average of the moments for event shapes in e ^?+? e??→hadrons within the context of next-to-leading order (NLO) perturbative QCD prediction in dispersive model is studied. Moments used in this article are $\langle {1-T}\rangle$ , $\langle \rho\rangle$ , $\langle {B_{\rm T}}\rangle$ and $\langle {B_{\rm W} }\rangle$ . We extract α _s, the coupling constant in perturbative theory and α ₀ in the non-perturbative theory using the dispersive model. By fitting the experimental data, the values of $\alpha_{\rm s} ({M_{\rm Z^0} })=0.1171\pm 0.00229$ and $\alpha_0 \left( {\mu_{\rm I} =2\,{\rm GeV}} \right)=0.5068\pm 0.0440$ are found. Our results are consistent with the above model. Our results are also consistent with those obtained from other experiments at different energies. All these features are explained in this paper.     

Preparation,structure and properties of La<Subscript>0.67</Subscript>Pb<Subscript>0.33</Subscript>(Mn<Subscript>1-x</Subscript>Co<Subscript>x</Subscript>)O<Subscript>3-δ</Subscript>

La_0.67Pb_0.33(Mn_1-xCo_x)O_3-δ ceramics with x=0, 0.01, 0.03, 0.06, 0.1 and 0.15 have been prepared in a two-step procedure. Precursor gels were made by the wet chemical malic acid method. The gels were calcined and then converted into ceramics by heat treatment at 950 °C and 1000 °C in air. X-ray diffraction showed that the compounds were phase pure. The crystal structure symmetry of the compounds was confirmed to be rhombohedral (space group R3̄c) for the whole investigated range of x. All compounds undergo a paramagnetic–ferromagnetic phase transition between 335 K and 225 K. The basic magnetic characteristics such as the Curie temperature , the paramagnetic Curie temperature θ, the effective magnetic moment and the saturated magnetization decrease with increasing Co doping. The ferromagnetic transition is accompanied by an anomaly in the electrical resistance for all compounds. The high-temperature insulator–metal transitions () do not coincide with the relevant . A large magnetoresistance peak of about 15% was observed for all compounds at . PACS 72.80.Ga; 75.47.Lx; 75.60.Ej