The photino mass and γγ˜γ˜ production in e+e− annihilation

We present the exact calculation of the cross section for the process e⁺e^? → $\gamma \stackrel{?}{\gamma }\stackrel{?}{\gamma }$ with finite photino mass. The process is one of the best places to search for the stable photino at PETRA energy.     

Theoretical investigation of parity violation in p→α scattering

Calculations are presented of the parity-non-conserving (PNC) analyzing power A_z for longitudinally polarized incoming protons in elastic $\overrightarrow{p}\alpha$ scattering below ～50 MeV. The results are given in terms of the PNC as well as the regular, parity-conserving (PC) meson-nucleon coupling constants for single π-, ρ- and ω-exchange. The reliability and parameter dependence of the calculations are discussed in detail. The PC on-shell scattering parameters play an important role in particular for the angular dependence of A_z, which must be known for the actual analysis of measurements and are taken from experiments directly (phase analysis) rather than model calculations. The PNC scattering amplitudes are calculated in DWBA with optical-model wave functions properly antisymmetrized.Short-range correlations between nucleon pairs are taken into account by a Jastrow factor whose appropriate choice is discussed in detail. While absorption from the elastic channel is taken into account by the optical-model wave function, intermediate breakup channels are not included explicitly in the matrix elements.     

Relevance of inter-site Coulomb repulsion on high-Tc superconductivity within t−J−V model

The relevance of inter-site Coulomb repulsion (V) in the hole-doped cuprates is explored within $t?J?V$ model. An exact diagonalization (ED) technique is employed to investigate some ground state and thermodynamic properties of the model for various hole-doping. Results show that electron-electron ($e?e$) correlation is maximum between the next-nearest-neighbor (NNN) sites which decreases sharply at distances longer than √2 times the lattice spacing. Unlike hole-concentration, Coulomb repulsion reduces effective hopping amplitude. Our results suggest that in this hole-doped system, inter-site Coulomb repulsion favors d-wave pairing. Specific heat curves show characteristic single broad peaks where the peak-height decreases with doping concentration. From specific heat and entropy curves, one can expect a superconducting state at $<h>=0.25$.     

Evidence for soft modes at q→≠0 ≠ 0 in the far-infrared spectrum of Rb2ZnBr4

The possibility to observe optically inactive and $\overrightarrow{q}\ne 0$ ≠ 0 soft modes in an indirect way by using far-infrared techniques is investigated. Using the fact that, due to anharmonicity, all modes of lattice vibrations are coupled with each other, the softening of one particular mode can be seen indirectly in the damping of other modes. By applying this idea to the modulated structure Rb₂ZnBr₄, the infrared inactive soft mode at the normal-incommensurable transition, the soft phason mode at the lock-in transition as well as a soft mode behaviour at an intermediate temperature have been observed.     

Search for new d0 half-metallic materials: theoretical investigation on KCaC1−xSix (x = 0; 0.25; 0.5; 0.75 and 1) compounds

In recent years, the investigations on d⁰ half-metallic materials have become the new trend in the search of novel materials for applications in spintronic devices. In this work, the structural, electronic and magnetic properties of KCaC${}_{1?x}$Si_x (x = 0; 0.25; 0.5; 0.75 and 1) compounds have been theoretically studied using the full-potential linearized augmented plane wave (FP-LAPW) method within framework of the density functional theory. The generalized gradient approximation scheme as proposed by Wu-Cohen (GGA-WC) and Tran-Blaha modified Becke-Johnson exchange potential with improved parameterization by Koller are adopted for the treatment of electron exchange-correlation. All considered materials show half-metallic characteristics with semiconducting majority spin channel and metallic minority one. The total spin magnetic moment is 1μ_B for ternary alloys and 4μ_B for quaternary compounds. Our obtained results suggest that these materials could be promising candidate for spintronic applications.     

B0 ? ffB^0 \to \phi\phi decay in perturbative QCD approach

The rare decay can occur only via the penguin annihilation topology in the standard model. We calculate this channel in the perturbative QCD approach. The predicted branching ratio is very small: around 10^-8. We also give the polarization fractions, which show that the transverse polarization contribution is comparable to the longitudinal one, due to a big transverse contribution from factorizable diagrams. The small branching ratio in SM makes it sensitive to any new physics contributions.Received: 29 January 2005, Published online: 28 April 2005     

Logics from ?{￠}\sqrt{^{\prime}} Quasi-MV Algebras

The purpose of the present article is to extend the scope of some investigations about abstract logics arising quite naturally out of Quasi-MV algebras (for short, qMV algebras) also to ?{^￠}\sqrt{^{\prime}} qMV algebras. We will therefore introduce, mutually compare and (in some cases) axiomatise several logics arising out of the variety of ?{^￠}\sqrt{^{\prime}} qMV algebras and out of some important subclasses of such. Subsequently, we will investigate the same logics by resorting to the methods and techniques of abstract algebraic logic.     

η, h￠ \eta{^\prime} → πl+l- in a chiral unitary approach

The decays η, → π⁺π^- l ⁺ l ^- (with l = e,μ are investigated within a chiral unitary approach which combines the chiral effective Lagrangian with a coupled-channels Bethe-Salpeter equation. Predictions for the decay widths and spectra are given.     

Triviality of ϕ44 theory: Small volume expansion and new data

We study a renormalized coupling g and mass m   in four-dimensional ?⁴${?}^4$ theory on tori with finite size z=mL$z=mL$. Precise numerical values close to the continuum limit are reported for z=1,2,4$z=1,2,4$, based on Monte Carlo simulations performed in the equivalent all-order strong coupling reformulation. Ordinary renormalized perturbation theory is found to work marginally at z=2$z=2$ and to fail at z=1$z=1$. By exactly integrating over the constant field mode we set up a renormalized expansion in z and compute three nontrivial orders. These results reasonably agree with the numerical data at small z. In the new expansion, the universal continuum limit exists as expected from multiplicative renormalizability. The triviality scenario is corroborated with significant precision.     

J/ψ production in pp collisions at ?s \sqrt s = 200GeV in the STAR experiment

In this work we present the J/ψ measurement in p+p collisions within the STAR collaboration Quarkonium program. This measurements aim to be the baseline measurement of a more comprehensive systematic study of quarkonium states production in order to understand their in medium modification. Here we report the total cross section and p _T distribution, and find them to be consistent with pQCD CEM predictions as well as to previous measurements at the same center-of-mass energy.     

Measurement of D* mesons in jets from p + p collisions at ?s \sqrt s = 200 GeV

We report the measurement of charged D* mesons in jets produced in proton-proton collisions at a center of mass energy $ \sqrt s $ \sqrt s = 200 GeV with the STAR experiment at RHIC. The production rate is found to be N(D*⁺ + D*⁻)/N (jet) = 0.015 ± 0.008 (stat) ± 0.007 (sys) for D* mesons with fractional momenta 0.2 < z < 0.5 in jets with 11.5 GeV mean transverse energy. This rate is consistent with perturbative QCD evalulation of gluon splitting into a pair of charm quarks and subsequent hadronization.     

Baryon-charge transfer and production asymmetry of Λ0/ [`(L)] 0\bar \Lambda ^0 in hadron interactions

Predictions were made for asymmetry between production spectra of Λ⁰ and at the energy of LHC experiments. The value of A(s) should be situated in the corridor between two curves calculated in the quark-gluon string model with two possible values of intercept α _SJ(0) = 0.5 and 0.9. Both curves describe the asymmetries measured at lower energies up to RHIC experiments. The data of the H1 experiment can be fitted only with α _SJ(0) = 0.9. The text was submitted by the author in English.     

Stopping in ?{sNN } \sqrt {s_{NN} } = 62.4 GeV Au+Au collisions

Stopping in heavy ion collisions has been measured at several energies from AGS to RHIC (spanning $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 5 GeV to $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV).The systematics of stopping hint the onset of a collision regime that might include LHC energies. Stopping in $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 62.4 GeV Au+Au collisions contribute to the understanding of different collision systems.