Infrared transmission study of Pr<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>CuO<Subscript><Emphasis Type="Bold">4</Emphasis></Subscript> crystal-field excitations

We present an infrared crystal-field study of Pr₂CuO₄ single crystals and thin films. Excitations from the ground state multiplet ³H₄ to the ³H₅, ³H₆, ³F₂ and ³F₃ excited multiplets are observed in both single crystals and thin films. A precise set of crystal-field parameters, that reproduces the energy and the symmetry of the levels, is determined. Received 25 April 2001     

Crystal structure and optical properties of germanates <Emphasis Type="Italic">Ln</Emphasis><Subscript>2</Subscript>Ca(GeO<Subscript>3</Subscript>)<Subscript>4</Subscript> (<Emphasis Type="Italic">Ln</Emphasis> = Gd,Ho, Er,Yb, Y)

This paper reports on the results of structural and optical investigations of a new class of layered compounds Ln ₂Ga(GeO₃)₄ (Ln = Gd, Ho, Er, Yb, Y), which are promising for the use in photonics as converters of laser radiation.     

Interplay between grand unification and supersymmetry in <Emphasis Type="BoldItalic">SU</Emphasis>(5) and <Emphasis Type="BoldItalic">E</Emphasis> <Subscript> <Emphasis Type="Bold">6</Emphasis> </Subscript>

Some aspects of minimal supersymmetric renormalizable grand unified theories are reviewed here. These include some constraints on the model parameters from the Higgs and light fermion masses in SU(5), and the issues of symmetry breaking, doublet–triplet splitting and fermion masses in E₆.     

Thermopower of <Emphasis Type="Italic">R</Emphasis>B<Subscript>12</Subscript> dodecaborides (<Emphasis Type="Italic">R</Emphasis> = Ho,Er, Tm,Lu)

Detailed measurements of the Seebeck coefficient S(T) in a broad range of temperatures (T = 2–300 K) have been performed for the first time for RB₁₂ dodecaborides (R = Ho, Er, Tm, Lu) in paramagnetic (diamagnetic for LuB₁₂) and antiferromagnetic states. At intermediate temperatures (10–300 K), the thermopower is determined by the interaction of carriers with phonon modes, which are related to the oscillations of rare-earth atoms in the framework of atomic clusters B₁₂. A comparative analysis of the parameters determining photon drag the thermopower related to the phonon drag and the results of galvanomagnetic measurements shows evidence for a significant effect of spin fluctuations on the behavior of charge transport characteristics in RB₁₂ compounds with strong electron correlations.     

Covalent magnetism in the RFe <Emphasis Type="Bold">6</Emphasis>Ge <Emphasis Type="Bold">6</Emphasis> series

The electronic structure of the RFe ₆ Ge ₆ compounds ( R = Sc, Lu, Ti, Zr, Hf and Nb) of HfFe ₆ Ge ₆ -type structure has been studied using the muffin-tin Korringa-Kohn-Rostoker method in a non-relativistic approach. The chemical bonding is analyzed based on the l-decomposed site projected densities of states. Spin-dependent changes in the R nd- Fe 3d covalent bond are shown to be responsible for the experimentally observed rise in the Fe moment and hyperfine field upon increasing the R valency. The limited quantitative agreement between theoretical and experimental values is interpreted as being due to a non-negligible orbital moment and to a significant asphericity in the spin density at the iron site. The theoretical results also forecast a strong increase of the Ge(2e) transferred hyperfine field with the R valency. Received 20 December 2002 Published online 4 June 2003 RID="a" ID="a"e-mail: Thomas.Mazet@lcsm.uhp-nancy.fr RID="b" ID="b"Associé au CNRS (UMR 7555)     

Fermion Localization on the <Emphasis Type="Italic">orbifold</Emphasis><Emphasis Type="Italic">S</Emphasis><Subscript>1</Subscript>/<Emphasis Type="Italic">Z</Emphasis><Subscript>2</Subscript>

The hierarchical structure of fermion masses of the Standard Model is explained in split fermion models by localizing the fermions at different points in an extra dimension. We consider split fermion models with two bulk scalars compactified on an orbifold. In the static case we find analytical expression for the localizer. We also address the issue of stability of the localizer. We also find exact solutions for the fermion zero modes. We explore the parameter space of the model. We find ample opportunity for construction of phenomenologically viable theories exist.     

The Dirac Operator on <Emphasis Type="Italic">SU</Emphasis><Subscript><Emphasis Type="Italic">q</Emphasis></Subscript>(2)

We construct a 3⁺-summable spectral triple over the quantum group SU_q(2) which is equivariant with respect to a left and a right action of The geometry is isospectral to the classical case since the spectrum of the operator D is the same as that of the usual Dirac operator on the 3-dimensional round sphere. The presence of an equivariant real structure J demands a modification in the axiomatic framework of spectral geometry, whereby the commutant and first-order properties need be satisfied only modulo infinitesimals of arbitrary high order.Partially supported by Polish State Committee for Scientific Research (KBN) under grant 2 P03B 022 25.Regular Associate of the Abdus Salam ICTP, Trieste.     

Spectral Action on <Emphasis Type="Italic">SU</Emphasis><Subscript><Emphasis Type="Italic">q</Emphasis></Subscript>(2)

The spectral action on the equivariant real spectral triple over is computed explicitly. Properties of the differential calculus arising from the Dirac operator are studied and the results are compared to the commutative case of the sphere . UMR 6207, – Unité Mixte de Recherche du CNRS et des Universités Aix-Marseille I, Aix-Marseille II et de l’Université du Sud Toulon-Var, Laboratoire affilié à la FRUMAM – FR 2291. Partially supported by Polish Government grants 189/6.PRUE/2007/7; 115/E-343/SPB/6.PR UE/DIE and N 201 1770 33.     

<Emphasis Type="Italic">SU</Emphasis>(3)-Instantons and <Emphasis Type="Italic">G</Emphasis><Subscript>2</Subscript>,<Emphasis Type="Italic">Spin</Emphasis>(7)-Heterotic String Solitons

Necessary and sufficient conditions to the existence of a hermitian connection with totally skew-symmetric torsion and holonomy contained in SU(3) are given. A formula for the Riemannian scalar curvature is obtained. Non-compact solution to the supergravity-type I equations of motion with non-zero flux and non-constant dilaton is found in dimension 6. Non-conformally flat non-compact solutions to the supergravity-type I equations of motion with non-zero flux and non-constant dilaton are found in dimensions 7 and 8. A Riemannian metric with holonomy contained in G₂ arises from our considerations and Hitchin’s flow equations, which seems to be new. Compact examples of SU(3),G₂ and Spin(7) instanton satisfying the anomaly cancellation conditions are presented.     

Isospin breaking in <Emphasis Type="BoldItalic">K</Emphasis><Subscript><Emphasis Type="BoldItalic">l4</Emphasis></Subscript> decays

Data on K _e4 decays allow one to extract experimental information on the elastic π π scattering amplitude near threshold, and to confront the outcome of the analysis with predictions made in the framework of QCD. These predictions concern an isospin symmetric world, while experiments are carried out in the real world, where isospin-breaking effects—generated by electromagnetic interactions and by the mass difference of the up and down quarks—are always present. We discuss the corrections required to account for these, so that a meaningful comparison with the predictions becomes possible. In particular, we note that there is a spectacular isospin-breaking effect in K _e4 decays. Once it is taken into account, the previous discrepancy between NA48/2 data on K _e4 decays and the prediction of π π scattering lengths disappears.     

<Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) Cosmology from <Emphasis Type="Italic">q</Emphasis>-theory

From a macroscopic theory of the quantum vacuum in terms of conserved relativistic charges (generically denoted by q ^(a) with label a), we have obtained, in the low-energy limit, a particular type of f(R) model relevant to cosmology. The macroscopic quantum-vacuum theory allows us to distinguish between different phenomenological f(R) models on physical grounds. The text was submitted by the authors in English.     

Quark diagram analysis of <Emphasis Type="Italic">B</Emphasis>-meson emitting vector (<Emphasis Type="Italic">V</Emphasis>) and vector (<Emphasis Type="Italic">V</Emphasis>) mesons

This paper presents the two body weak nonleptonic decays of B-mesons emitting vector (V) and vector (V) mesons within the framework of the diagrammatic approaches at flavor SU(3) symmetry. We have investigated exclusive two body decays of B-meson using model independent quark diagram scheme. We have shown that the recent measurement of the two body exclusive decays of B-mesons can allow us to determine the magnitude and even sign of the QD amplitude for B → VV decays. Therefore, we become able to make few predictions for their branching fractions.     

Comparative study of hydrofullerides C<Subscript><Emphasis Type="Bold">60</Emphasis></Subscript>H<Subscript><Emphasis Type="BoldItalic">x</Emphasis></Subscript> synthesized by direct and catalytic hydrogenation

Hydrofullerides with hydrogen content up to 5 wt.% were obtained by direct and catalytic reactions with H₂ gas. Hydrogen content was monitored in situ using a gravimetric system, and verified by chemical analysis ex situ. It was found that pure C₆₀ reacts rapidly when exposed to H₂ gas at 673 K and 50–100 bar. Gravimetric study of this reaction showed that hydrogenation is saturated at about 5 wt.% of hydrogen. The mass of the sample goes through a maximum and with a longer reaction time its weight starts to decrease. This proves that hydrofullerides with high hydrogen content are not stable and strong hydrogenation results in the collapse of C₆₀ molecules. XRD studies showed that samples prepared by direct hydrogenation without a catalyst retain an original fcc structure with an increase of the cell parameter a up to 15.1 Å. Catalytic hydrogenation of C₆₀ with H₂ gas results in a decrease of the reaction temperature and formation of hydrofullerides with different types of crystal structures. PACS 61.48.+c; 61.10.Nz; 81.05.Tp     

Interacting Dark Energy in the Dark <Emphasis Type="Italic">S</Emphasis><Emphasis Type="Italic">U</Emphasis>(2)<Subscript><Emphasis Type="Italic">R</Emphasis></Subscript> Model

We explore the cosmological implications of the interactions among the dark particles in the dark SU(2) _R model. It turns out that the relevant interaction is between dark energy and dark matter, through a decay process. With respect to the standard ΛCDM model, it changes only the background equations. We note that the observational aspects of the model are dominated by degeneracies between the parameters that describe the process. Thus, only the usual Λ CDM parameters such as the Hubble expansion rate and the dark energy density parameter (interpreted as the combination of the densities of the dark energy doublet) could be constrained by observations at this moment.     

Negative thermo-optical coefficients and athermal directions in monoclinic KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> and KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> laser host crystals in the visible region

The temperature dependence of three principal refractive indices of the biaxial KGd(WO₄)₂ and KY(WO₄)₂ crystals in the temperature range of 288–673 K was measured at wavelengths of 438.5 and 632.8 nm. Their thermo-optical coefficients (TOC) of the first and second orders were determined on the basis of the experimental data obtained. TOC were found to be negative for the n_g and n_p refractive indices of the KY(WO₄)₂ crystal and for the n_g refractive index of the KGd(WO₄)₂ crystal. It was established that in a fairly wide temperature range contributions of the positive and negative TOC to the refractive index of a light wave propagating in these crystals in certain directions compensate each other. Such athermal directions were determined for the index ellipsoid principal planes of these crystals on the basis of experimental data. PACS 78.20.Ci; 78.20.Nv     

Discussion of isomeric ratios in (<Emphasis Type="Italic">p,n</Emphasis>) and (<Emphasis Type="Italic">d</Emphasis>, 2<Emphasis Type="Italic">n</Emphasis>) reaction

Isomeric ratios (IR) in the (p, n) and (d, 2n) reactions are considered. The dependence of IR values on the projectile type and energy, the target- and product-nucleus spin, the spin difference between the isomeric and ground states of products, and the product mass number is discussed. The isomeric ratios for 46 product nuclei (from ^44m,gSc to ^127m,gXe) obtained in reactions where target and product nuclei have identical mass numbers were calculated at energies from the reaction threshold to 50 MeV (with a step of ΔE = 1 MeV). The calculations in question were performed with the aid of the TALYS 1.4 code package. The calculated IR values were compared with their experimental counterparts available from the literature (EXFOR database). In the majority of cases, the calculated IR values agree well with the experimental data in question. It is noteworthy that the IR values obtained in (d, 2n) reactions are substantially greater than those in (p, n) reactions.     

The <Emphasis Type="Italic">q</Emphasis>-boson-fermion realizations of the quantum superalgebra <Emphasis Type="Italic">U</Emphasis><Subscript><Emphasis Type="Italic">q</Emphasis></Subscript>(<Emphasis Type="Italic">osp</Emphasis>(1/2))

We show that our construction of realizations for algebras and quantum algebras can be generalized to quantum superalgebras too. We studyan example of quantum superalgebra U _q (osp(1/2)) and give the boson-fermion realization with respect to one pair of q-boson operators and one pair of fermions.     

The electromagnetic effects in <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis>4</Subscript> decay

The final-state interaction of pions in K _e4 decay allows to obtain the value of the isospin and angular-momentum-zero ππ scattering length a ₀ ⁰ .We take into account the electromagnetic interaction of pions and isospin-symmetry-breaking effects caused by different masses of neutral and charged pions and estimate the impact of these effects on the procedure of scattering-length extraction from K _e4 decays.