Neutral currents within beyond the standard model

We present new, model-independent analyses of the observables in low-energy neutral-current experiments in the neutrino-hadron, neutrino-electron, electron/muon-hadron and electron- muon/tau sectors. We combine them with the latest experimental measurements of the W and Z masses to make global fits in the context of the standard model and of superstring-inspired models. We find in the standard model that sin ²θ _w = 0.228 ± 0.004 if ϱ is fixed to be 1, whilst a two parameter fit yields sin ²θ _w = 0.229 ± 0.006 and ϱ = 1.001 ± 0.007. This new value of sin ²θ _w for ϱ = 1 lies uncomfortably outside the predicted region of the minimal SU(5) model, but is consistent with supersymmetric SU(5) models. In the minimal standard model with ϱ = 1 and equal Higgs and Z masses we find that m_t<168 GeV at the 90% confidence level. We establish lower bounds on the masses of additional neutral gauge bosons Z′ in three superstring-inspired models and upper limits on their mixing with the standard model Z ⁰. In particular, we find that m_Z′129 GeV at the 90% confidence level in a minimal rank-5 superstring-inspired model with canonical Higgs structure.     

Space–time structure of new physics with polarized beams at the linear collider

We approach the issue of the discovery of new physics at high energies associated with the proposed International Linear Collider in the presence of longitudinal as well as transverse electron and positron beam polarization. We determine the beam polarization dependence and the angular distribution of a particle of arbitrary spin in a one-particle inclusive final state produced in e⁺e^- collisions through the interference of γ or Z amplitude with the amplitude from new interactions having arbitrary space–time structure. We thus extend the results of Dass and Ross, proposed at the time of the discovery of neutral currents, to beyond the standard model currents. We also extend the case of e⁺e^- annihilation in the s-channel to the production of bosons due to t- and u-channel processes. Our work provides an approach to model-independent determination of the space–time structure of beyond the standard model interactions. We briefly discuss applications of the framework to popular extensions of the standard model, and demonstrate that our framework is general enough to account for certain results in the minimal supersymmetric standard model.     

Neutron pick-up pion transfer reactions for the formation of deeply bound pionic atoms in 208Pb

We study (n, d) and (d, ³He) reactions on ²⁰⁸Pb leading to deeply bound pionic atoms with one neutron hole being left. We develop a theoretical model to calculate cross sections of deeply bound pionic atoms and quasi-elastic pion production. The results are compared with data which have been obtained so far. We show that the theoretical model describes the data of both reactions well.     

Hopf Solitons and Area-Preserving Diffeomorphisms of the Sphere

We consider a (3+1)-dimensional local field theory defined on the sphere S ². The model possesses exact soliton solutions with nontrivial Hopf topological charges and an infinite number of local conserved currents. We show that the Poisson bracket algebra of the corresponding charges is isomorphic to that of the area-preserving diffeomorphisms of the sphere S ². We also show that the conserved currents under consideration are the Noether currents associated to the invariance of the Lagrangian under that infinite group of diffeomorphisms. We indicate possible generalizations of the model.     

Quark spin-isospin sum rules and the adler-weisberger relation in nuclei

We use a quark model to extend the classical Gamow-Teller sum rule for the difference of the β^?andβ⁺ strengths to excitations of the nucleon (mainly the Δ isobar).A schematic model illustrates the realization of the new sum rule when a particle-hole force is introduced. We discuss the connection of our result with the model-independent Adler-Weisberger sum rule.     

Readjustment of the Bohr stopping force from energies of keV/n to a few tens of MeV/n ions in elemental targets

An analytical approach for the electronic stopping force for non-relativistic energies that has no adjustable parameters has been developed. The approach combines the Bohr model for the close collisions and the Firsov model for the distant collisions. In order to combine the two models, a probabilistic model was introduced. We have applied our model to ¹⁶O in ¹²C, ¹⁶O in ²⁷Al, ⁸⁴ Kr in ²⁷Al, ⁵Li in ¹²C, ¹²C in ¹²C, and ¹³²Xe in ¹²C systems and compared with SRIM/MSTAR software, the original Bohr model, the Firsov model and available experimental data. We have found that the calculated electronic stopping force values are in agreement with the general qualitative behaviour of the electronic stopping force as a function of particle velocity reported in the literature. The proposed analytical formula is expected to be valid for other projectile-target combinations but more experimental data are needed to verify this assumption.     

The amplitude structure of the processesK - p→ϱ-∑ (1385) andK - p→Φ ∑0 (1385) at 4.2 GeV/c

We present model-independent transversity amplitudes for the processesK ^- p→?^-∑ (1385) andK ^- p→Φ ∑⁰ (1385) at 4.2 GeV/c. We also perform a model dependent analysis and compare the resulting helicity amplitudes with the predictions of a simple exchange model. Implications for future model building are discussed.     

Investigation for a Drastic Change of the Core in 23O and 24O

We study the radius and energies of oxygen isotopes towards the neutron drip-line. The abrupt increase of the radius at ²³O is investigated with two different approaches; the m-scheme cluster-orbital shell model (COSM) and a simplified model approach with the core plus one and two valence neutrons. We investigate properties of the oxygen isotopes by changing the radius of the ¹⁶O-core in the m-scheme COSM approach and obtain the result that the broad structure of ¹⁶O is favored in the ²³O and ²⁴O. In the simplified model approach, we estimate the magnitude of the change of the size of ²²O in ²³O and ²⁴O.     

Dopant control over the crystal morphology of ceramic materials

Doping is a common way to activate the behavior of ceramics. Its effect is not limited to the bulk: segregation of dopants to the surfaces also yields a way to modify, and ultimately control the crystal morphology. We propose a model that allows us to calculate the surface energy beyond the Langmuir isotherm for doped and defective surfaces from atomic-level simulations. The model also allows us to account for different compositions between the bulk and surface. Computational materials design can thus be applied to optimize simultaneously the crystal behavior at the atomic (surface structure and composition) and mesoscopic (crystal size and shape) length scales. We exemplify the model with orthorhombic CaTiO₃ perovskite doped with Mg²⁺, Fe²⁺, Ni²⁺, Sr²⁺, Ba²⁺ and Cd²⁺ ions, by predicting the effect that different dopants and dopant concentrations have on the crystal morphology. We find that a higher proportion of reactive {0 2 1} and {1 1 1} surfaces are exposed with the presence of divalent Mg²⁺, Fe²⁺ and Ni²⁺ ions than in the undoped material and in perovskite doped with Ba²⁺ and Sr²⁺. Cd²⁺ has only minor effects on crystal morphologies. These findings have important implications for predicting the reactivity of crystals doped with different ions and we show how this can be related to a simple parameter such as the ionic radius. We have tested our newly derived model by comparison with laboratory flux grown single crystals of CaTiO₃, (Ni, Ca)TiO₃ and (Ba, Ca)TiO₃ and find excellent agreement between theory and experiment.     

A test for the gluon selfcoupling in the reactionse + e −→4 jets andZ 0→4 jets

We consider the reactionse ⁺ e ^?→γ^*→4 jets andZ ^o→4 jets with the 4 jets coming in two pairs of essentially back to back jets of high and low energy. We calculate the angular distribution of the low energy jet axis with respect to the high energy jet axis in QCD, in an abelian gluon model “QED” and a phase space model (PS). Using simple helicity arguments we show that our angular distribution is very sensitive to the triple gluon coupling in QCD. This is then confirmed by a complete calculation. Our correlation offers, therefore, a direct test for QCD as a non-abelian gauge theory.     

Phenomenology of the 0.7 conductance feature

We describe a phenomenological model for the conductance feature near 0.7×2e²/h that occurs in quantum point contacts. We focus on the transconductance at finite source–drain bias and contrast our model with the results expected from a single-particle picture. Good agreement is seen in comparing the model with experimental data, taken on ultra-low-disorder GaAs induced electron systems. Although simple, our phenomenology suggests important boundary conditions for an underlying microscopic theory.     

Study of non-radiative silicon deexcitation in an oxygen atmosphere using the differential measurement of the excited state lifetimes

Having developed a new method of differential lifetime measurement using atomic ionoluminescence as an excitation process, we applied this method to a monocrystaline silicon sample in an oxygen atmosphere of variable pressure. We found decreased values of the experimental lifetimes concerning levels 4s ³ P ⁰ and 4s ¹ P ⁰, which are more marked when the oxygen pressure increases. This tends then towards a saturation of the observed phenomenon. We propose, in agreement with other authors, an explanation which is based on the existence of non-radiative deexcitations. We present also a mathematical model for calculating this transition effect on the lifetime measurements. We consider that it is possible to take advantage of this experimental lifetime variation to determine a parameter of the model which characterises the non-radiative deexcitations. This measuring method appears to be a simple and original procedure for the study of certain nonradiative transitions.     

High energy proton-carbon scattering in the alpha-particle model

We investigate elastic and inelastic 0⁺–2⁺ high energy proton-¹²C scattering in the alpha-particle model. We use a rigid equilateral triangle nuclear wave function with a Gaussian dispersion function allowing theα-particles of the¹²C-nucleus to deviate from their most probable positions at the triangle vertices. Expressions for the differential scattering cross sections are deduced using Glauber multiple diffraction theory. Thus we need thep?α-particle scattering amplitude, which is calculated from a Gaussian nucleon-nucleon profile function. Numerical calculations show that the model reproduces the experimental results onp?α andp-¹²C scattering.     

The decay of theτ lepton to six pions

We present the branching ratio predictions of an isospin statistical model forτ decays to four, five and six pions. Limits on the branching ratios of the three possible six pionτ decay modes using the Conserved Vector Current (CVC) Hypothesis and thee ⁺ e ^?→6π cross section data are also presented. We find that the isospin model prediction is in good agreement with the well-measured four pion decay modes and consistent with the five pion decay modes. However, we find that some of the recent six pionτ measurements do not agree with the isospin model and the CVC prediction.     

Theoretical expectations for σtot at the large hadron collider

In this note, we summarize and compare various model predictions forpp total cross-section σ _tot ^pp , giving an estimate of the range of predictions for the total cross-section, σ _tot ^pp expected at the LHC. We concentrate on the results for σ _tot ^pp obtained in a particular QCD based model of the energy dependence of the total cross-section, including the effect of soft gluon radiation. We obtain the range of predictions in this model by exploring the allowed range of model parameters. We further give a handy parametrisation of these results which incidentally spans the range of various other available predictions at the LHC as well     

The large probability of the 0+ ground states

We investigate the dominance of 0⁺ states as the lowest states in shell model calculations with random two-body interactions in a single j-shell. We have found an explanation of the large probability of the 0⁺ ground state. Received: 1 May 2001 / Accepted: 4 December 2001     

Equation of state for the Universe from similarity symmetries

In this paper we proposed to use the group of analysis of symmetries of the dynamical system to describe the evolution of the Universe. This method is used in searching for the unknown equation of state. It is shown that group of symmetries enforce the form of the equation of state for noninteracting scaling multifluids. We showed that symmetries give rise to the equation of state in the form p =-Λ + w ₁ρ(a) + w ₂ a ^β + 0 and energy density ρ = Λ+ρ₀₁ a ^-3(1+w) +ρ₀₂ a ^α +ρ₀₃ a ^-3, which is commonly used in cosmology. The FRW model filled with scaling fluid (called homological) is confronted with the observations of distant type Ia supernovae. We found the class of model parameters admissible by the statistical analysis of SNIa data.We showed that the model with scaling fluid fits well to supernovae data. We found that Ω_m,0 ≃ 0.4 and n ≃ -1 (β = -3n), which can correspond to (hyper) phantom fluid, and to a high density universe. However if we assume prior that Ω_m,0 = 0.3 then the favoured model is close to concordance ΛCDM model. Our results predict that in the considered model with scaling fluids distant type Ia supernovae should be brighter than in the ΛCDM model, while intermediate distant SNIa should be fainter than in the ΛCDM model. We also investigate whether the model with scaling fluid is actually preferred by data over ΛCDM model. As a result we find from the Akaike model selection criterion: it prefers the model with noninteracting scaling fluid.     

Radiation-Transfer Modeling of the Cloud L1544 in the HCO+ and HC18O+ Emission Lines

We study the formation of HCO⁺ and HC¹⁸O⁺ emission lines in the cloud L1544. The radiation transfer is modeled numerically, and the line intensities for different impact parameters are calculated. It is shown that a decrease in the abundances of the studied molecules toward the object center is necessary for the formation of the observed line profile in the optically thin case. We consider various hydrodynamic models allowing for compression, turbulence, and different types of cloud rotation and find a model ensuring the best agreement with the observational data. Our numerical simulations are indicative of nonuniform rotation in L1544. Assuming that the object is spherically symmetric, we estimate the density and velocity of the medium within the framework of the selected model.