Final-state polarization in <Emphasis Type="Italic">B</Emphasis><Stack><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript><Superscript>0</Superscript></Stack> decays

Certain B _s ⁰→V ₁ V ₂ decays (V _i is a vector meson) can be related by flavor SU(3) symmetry to corresponding B _d ⁰→V ₃ V ₄ decays. In this paper, we show that the final-state polarization can be predicted in the B _s ⁰ decay, assuming polarization measurements of the B _d ⁰ decay. This can be done within the scenario of penguin annihilation (PA), which has been suggested as an explanation of the unexpectedly large transverse polarization in B→φ K ^*. PA is used to estimate the breaking of flavor SU(3) symmetry in pairs of decays. Two of these for which PA makes a reasonably precise prediction of the size of SU(3) breaking are (B _s ⁰→φ φ,B _d ⁰→φ K ^0*) and ( ). The polarization measurement in the B _d ⁰ decay can be used to predict the transverse polarization in the B _s ⁰ decay and will allow for testing of PA as well as the other assumptions in the analysis.     

Investigations of low <Emphasis Type="Italic">q</Emphasis><Subscript><Emphasis Type="Italic">a</Emphasis></Subscript> discharges in the SINP tokamak

Low edge safety factor discharges including very low q _a (1<q _a <2) and ultra low q _a (0<q _a <1) have been obtained in the SINP tokamak. It has been observed that accessibility of these discharges depends crucially on the fast rate of plasma current rise. Several interesting results in terms of different time scales like T _{q a} · τ _R etc have been obtained using a set of softwares developed at SINP. From fluctuation analysis of the external magnetic probe data it has been found that MHD instabilities m=1, n=1 and m=2, n=1 etc. play major role in the evolution of these discharges. To investigate the internal details of these discharges, an internal magnetic probe system has been developed using which current density j _φ and other related parameters have been estimated. By carrying out a resistive stability analysis, evidence of the above-mentioned MHD instabilities have again been found. The physical processes lying behind the accessibility and evolution of the low q _a discharges have been thoroughly investigated.     

Influence of <Emphasis Type="Italic">CP</Emphasis> and <Emphasis Type="Italic">CPT</Emphasis> on production and decay of Dirac and Majorana fermions

The consequences of CP and CPT invariance for production and subsequent decay of Dirac and Majorana fermions in polarized fermion-antifermion annihilation are analytically studied. We derive general symmetry relations for the production spin density matrix and for the three-particle decay matrices and obtain constraints for the polarization and the spin-spin correlations of Dirac and Majorana fermions. We prove that only for Majorana fermions the energy and opening angle distribution factorizes exactly into contributions from production and decay if CP is conserved. Received: 6 November 2001 / Revised version: 23 April 2002 / Published online: 12 July 2002     

On the mass,width and coupling constants of the <Emphasis Type="Italic">f</Emphasis><Subscript><Emphasis Type="Italic">0</Emphasis></Subscript>(980)

Using the pole approach we determine the mass and width of the f ₀ (980); in particular, we analyze the possibility that two nearby poles are associated to it. We restrict our analysis to a neighborhood of the resonance, using data for the phase shift and inelasticity, and the invariant mass spectrum of the decays. The formalism we use is based on unitarity and a generalized ver sion of the Breit-Wigner parameterization. We find that a single pole describes the f ₀ (980), the precise position depending upon the data used. As a byproduct, values for the and coupling constants are obtained. Received: 6 June 2002 / Revised version: 21 October 2002 / Published online: 3 March 2003     

The isospin-symmetry-breaking effects in <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis>4</Subscript> decays

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 ₀⁰.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.     

Leptonic constant of the pseudoscalar <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> meson

We calculate the leptonic constant for the pseudoscalar ground state of the B _c meson in the framework of a QCD-motivated potential model taking into account the two-loop anomalous dimension for the heavy quark current in nonrelativistic QCD as matched with full QCD.     

Re-evaluation of the LHC potential for the measurement of <Emphasis Type="Italic">m</Emphasis><Subscript><Emphasis Type="Italic">W</Emphasis></Subscript>

We present a study of the LHC sensitivity to the W boson mass based on simulation studies. We find that both experimental and phenomenological sources of systematic uncertainties can be strongly constrained with Z measurements: the lineshape, dσ _Z /dm, is robustly predicted, and its analysis provides an accurate measurement of the detector resolution and absolute scale, while the differential cross-section analysis, d² σ _Z /dydp _T , absorbs the strong interaction uncertainties. A sensitivity δ m _W ∼7 MeV for each decay channel (W→e ν, W→μ ν), and for an integrated luminosity of 10 fb⁻¹, appears as a reasonable goal.     

The determination of <Emphasis Type="Italic">α</Emphasis><Subscript><Emphasis Type="Italic">S</Emphasis></Subscript> from <Emphasis Type="Italic">τ</Emphasis> decays revisited

We revisit the determination of α _S (m _τ ²) using a fit to inclusive τ hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient K ₄ in the expansion of the Adler function, (2) new precision measurements from BABAR of e⁺e⁻ annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions, and (3) improved results from BABAR and Belle on τ branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty, introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative prediction of two different methods: fixed-order perturbation theory (FOPT) and contour-improved perturbative theory (CIPT). The corresponding theoretical uncertainties are studied at the τ and Z mass scales. The CIPT method is found to be more stable with respect to the missing higher order contributions and to renormalization scale variations. It is also shown that FOPT suffers from convergence problems along the complex integration contour. Nonperturbative contributions extracted from the most inclusive fit are small, in agreement with earlier determinations. Systematic effects from quark-hadron duality violation are estimated with simple models and found to be within the quoted systematic errors. The fit based on CIPT gives α _S (m _τ ²)=0.344±0.005±0.007, where the first error is experimental and the second theoretical. After evolution to M _Z we obtain α _S (M _Z ²)=0.1212±0.0005±0.0008±0.0005, where the errors are respectively experimental, theoretical and due to the evolution. The result is in agreement with the corresponding N³LO value derived from essentially the Z width in the global electroweak fit. The α _S (M _Z ²) determination from τ decays is the most precise one to date.     

<Emphasis Type="Italic">D</Emphasis>-Branes in the Euclidean <Emphasis Type="Italic">AdS</Emphasis><Subscript>3</Subscript> and <Emphasis Type="Italic">T</Emphasis>-Duality

We show that D-branes in the Euclidean AdS ₃ can be naturally associated to the maximally isotropic subgroups of the Lu–Weinstein double of SU(2). This picture makes very transparent the residual loop group symmetry of the D-brane configurations and gives also immediately the D-branes shapes and the σ-model boundary conditions in the de Sitter T-dual of the SL(2,C)/SU(2) WZW model.     

Passive Advection and the Degenerate Elliptic Operators <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

 We prove estimates for the stationary state n-point functions at zero molecular diffusivity in the Kraichnan model [13]. This is done by proving upper bounds for the heat kernels and Green's functions of the degenerate elliptic operators M _n that occur in the Hopf equations for the n-point functions. Received: 25 August 2001 / Accepted: 30 September 2002 Published online: 20 January 2003 Communicated by A. Kupiainen     

Properties of<Emphasis Type="Italic">B</Emphasis><Subscript>c</Subscript> meson

The mass spectrum ofcb meson is investigated with an effective quark-antiquark potential of the form -α_c/r +Ar ^νwith ν varying from 0.5 to 2.0. TheS andP-wave masses, pseudoscalar decay constant, weak decay partial widths in spectator model and the lifetime ofB _cmeson are computed. The properties calculated here are found to be in good agreement with other theoretical and experimental values at potential index,ν = 1     

The K<Emphasis Type="Italic">π</Emphasis> and <Emphasis Type="Italic">ππ</Emphasis> S-wave amplitude from D-meson decays

The issue of Kπ and ππ S-wave amplitude is addressed using decays of D-mesons. Model-independent measurements of the phases of the π ⁺ π ⁺ and K ^- π ⁺ S-wave amplitude from D ⁺→π ^- π ⁺ π ⁺ and D ⁺→K ^- π ⁺ π ⁺ decays are discussed. The result indicates a deviation from the phase of the K ^- π ⁺ S-wave amplitude obtained by scattering experiments. This could be interpreted as an indication of the presence of 3-body final-state interaction, or in other words, that the phases from production and scattering process cannot be directly compared.     

Phenomenological applications of<Emphasis Type="Italic">k</Emphasis><Subscript>T</Subscript>factorization

We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two-bodyB-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approach. PQCD results are compatible with present experimental data for charmless B-meson decays. We predict the possibility of large direct CP asymmetry in B⁰ → π⁺π⁻ (23 +7%) and B⁰ →K ⁺π⁻ (− 17 ± 5%). We also investigate the branching ratios, CP asymmetry and isospin symmetry breaking in radiativeB →(K*/ρ)γ decays.     

The <Emphasis Type="Italic">η</Emphasis>′ meson from lattice QCD

We study the flavour-singlet pseudoscalar mesons from first principles using lattice QCD. With N _f=2 flavours of light quarks, this is the so-called η ₂ meson and we discuss the phenomenological status of this meson. Using maximally twisted-mass lattice QCD, we extract the mass of the η ₂ meson at two values of the lattice spacing for lighter quarks than previously discussed in the literature. We are able to estimate the mass value in the limit of light quarks with their physical masses.     

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.     

Spin-dependent electron dynamics and recombination in GaAs<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys at room temperature

Conduction-electron spin polarization dynamics achieved by pulsed optical pumping at room temperature in GaAs_1−x N _x alloys with a small nitrogen content (x = 2.1, 2.7, and 3.4%) is studied both experimentally and theoretically. It is found that the photoluminescence circular polarization determined by the mean spin of free electrons reaches 40–45% and this giant value persists within 2 ns. Simultaneously, the total free-electron spin decays rapidly with the characteristic time ≈ 150 ps. The results are explained by spin-dependent capture of free conduction electrons on deep paramagnetic centers resulting in the dynamical polarization of bound electrons. A nonlinear theory of spin dynamics in the coupled system of spin-polarized free and localized carriers has been developed which describes the experimental dependencies, in particular, the electron spin quantum beats observed in a transverse magnetic field. The text was submitted by the authors in English.     

Resummed pQCD for <Emphasis Type="Italic">W</Emphasis><Superscript><Emphasis Type="Italic">±</Emphasis></Superscript> and <Emphasis Type="Italic">Z</Emphasis><Superscript>0</Superscript> transverse momentum spectra at RHIC and LHC

The transverse momentum distributions of W_± and Z₀ are predicted at RHIC and LHC. A resummation formalism with power corrections to the renormalization group equations is used. Shadowing effects are discussed and found to be unimportant at RHIC, but important for LHC. We study the enhancement of power corrections due to multiple scattering in nuclear collisions and numerically illustrate the weak effects of the dependence on the nuclear mass.     

SU(N) elastic rescattering in B and D decays

The treatment of elastic final-state interactions (FSIs) under a symmetry group is presented. The proposed model is based on Watson's theorem, i.e. on symmetry properties of the -matrix and on its unitarity. This theorem provides an easy way to introduce rescattering effects by defining final-state interactions mixing matrices. A symmetry group fixes the structure of such mixing matrices, and the passage from one group to another is studied (for example, SU(2) to SU(3)). Mixings among two charmless pseudoscalar decay product states will be systematically analyzed. Finally, these mixing matrices will be used on quark diagram parametrizations of B and D decay amplitudes. This will have some important consequences on the definition of quark diagrams. It will be argued that these diagrams should not contain any FSI effects, i.e. they should be real (except for CKM factors). FSIs are then introduced at the hadronic level, by mixing basic quark diagram topologies. Received: 17 December 1998 / Revised version: 17 February 1999 / Published online: 28 September 1999     

The <Emphasis Type="Italic">Φ</Emphasis>→K<Superscript>0</Superscript>¯<Emphasis Type="Italic">γ</Emphasis> decay

The scalar contributions to the radiative decay φ→K ⁰ˉ⁰ γ are studied within the framework of the Linear Sigma Model (LσM). Theoretical predictions for the associated subprocesses φ→f ₀ γ and φ→a ₀ γ as well as the ratio φ→f ₀ γ/a ₀ γ are also given.     

On the role of FSI in <Emphasis Type="Italic">K</Emphasis> → 2<Emphasis Type="Italic">π</Emphasis> decay

Contrary to widespread opinion that the final-state interaction (FSI) enlarges the amplitude 〈2π; I = 0|K ⁰〉, we argue that FSI is not able to increase the absolute value of this amplitude. The text was submitted by the author in English.