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AbstractAbstract

[en] Based on the light-cone (LC) framework and the k

_{T}factorization formalism, the transverse momentum effects and the different helicity components' contributions to the pion form factor F_{π}(Q^{2}) are recalculated. In particular, the contributions to the pion form factor from the higher-helicity components (λ_{1}+λ_{2}=±1), which come from the spin-space Wigner rotation, are analyzed in the soft and hard energy regions, respectively. Our numerical results show that the right power behavior of the hard contribution from the higher-helicity components can only be obtained by fully keeping the k_{T}dependence in the hard amplitude, and that the k_{T}dependence in LC wave function affects the hard and soft contributions substantially. As an example, we employ a model LC wave function to calculate the pion form factor and then compare the numerical predictions with the experimental dataPrimary Subject

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] We obtain a 3+2 neutrino spectrum within a left-right symmetric framework by invoking a singular double seesaw mechanism. Higgs doublets are employed to break SU

_{R}(2) and three additional fermions, singlets under the left-right symmetric gauge group, are included. The introduction of a singularity into the singlet fermion Majorana mass matrix results in a light neutrino sector of three neutrinos containing predominantly ν_{αL}, α=e,μ,τ, separated from two neutrinos containing a small ν_{αL}component. The resulting active-sterile mixing in the 5x5 mixing matrix is specified once the mass eigenvalues and the 3x3 submatrix corresponding to the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix are knownPrimary Subject

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] We study the mass spectrum of baryons with two and three charmed quarks. For double charm baryons the spin splitting is found to be smaller than standard quark-model potential predictions. This splitting is not influenced either by the particular form of the confining potential or by the regularization taken for the contact term of the spin-spin potential. We consistently predict the spectra for triply charmed baryons

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] The one-loop corrections to the lattice supersymmetric Ward-Takahashi identity (WTi) are investigated in the off-shell regime. In the Wilson formulation of the N=1 supersymmetric Yang-Mills theory, supersymmetry is broken by the lattice, by the Wilson term, and is softly broken by the presence of the gluino mass. However, the renormalization of the supercurrent can be realized in a scheme that restores the continuum supersymmetric WTi (once the on-shell condition is imposed). The general procedure used to calculate the renormalization constants and mixing coefficients for the local supercurrent is presented. The supercurrent not only mixes with the gauge invariant operator T

_{μ}. An extra mixing with other operators coming from the WTi appears. This extra mixing survives in the continuum limit in the off-shell regime and cancels out when the on-shell condition is imposed and the renormalized gluino mass is set to zero. Comparison with numerical results is also presentedPrimary Subject

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] We study the impact of light gauge bosons on neutrino physics. We show that they can explain the NuTeV anomaly and also escape the constraints from neutrino experiments if they are very weakly coupled and have a mass of a few GeV. Lighter gauge bosons with stronger couplings could explain both the NuTeV anomaly and the positive anomalous magnetic moment of the muon. However, in the simple model we consider in this paper (say a purely vectorial extra U(1) current), they appear to be in conflict with the precise measurements of ν

_{μ}-e, ν_{e}-e elastic scattering cross sections. The surprising agreement that we obtain between our naive model and the NuTeV anomaly for m_{Z'}∼ GeV may be a coincidence. However, we think it is interesting enough to deserve attention and perhaps a more careful analysis, especially since a new light gauge boson is a very important ingredient for the Light Dark Matter scenarioPrimary Subject

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] We examine the process of Compton scattering, in the presence of a Lorentz- and CPT-violating modification to the structure of the electron. We calculate the complete tree-level contribution to the cross section; our result is valid to all orders in the Lorentz-violating parameter. We find a cross section that differs qualitatively from the Klein-Nishina result at small frequencies, and we also encounter a previously undescribed complication that will arise in the calculation of many Lorentz-violation cross sections: The Lorentz violation breaks the spin degeneracy of the external states, so we cannot use a closure relation to calculate the unpolarized cross section

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] We point out that double distributions need not vanish at their boundary. Boundary terms do not change the ambiguity inherent in defining double distributions; instead, boundary conditions must be satisfied in order to switch between different decompositions. We analyze both the spin zero and spin one-half cases

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] Using relativistic kinetic theory, we study spherically symmetric, static equilibrium configurations of a collisionless Maxwell-Boltzmann gas with nonstandard self-interactions, modeled by an effective one-particle force. The resulting set of equilibrium conditions represents a generalization of the classical Tolman-Oppenheimer-Volkov equations. We specify these conditions for two types of Lorentz-like forces: one coupled to the 4-acceleration and the 4-velocity and the other one coupled to the Riemann tensor. We investigate the weak field limits in each case and show that they lead to various Newtonian type configurations that are different from the usual isothermal sphere characterizing the conventional Newtonian Maxwell-Boltzmann gas. These configurations could provide a plausible phenomenological and theoretical description of galactic dark matter halo structures. We show how the self-interaction may act phenomenologically as an effective cosmological constant and discuss possible connections with Modified Newtonian Dynamics (MOND)

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] In d=3 SU(N) gauge theory, we study a scalar-field theory model of center vortices, and their monopolelike companions called nexuses, that furnishes an approach to the determination of so-called k-string tensions. This model is constructed from stringlike quantum solitons introduced previously, and exploits the well-known relation between string partition functions and scalar-field theories in d=3. A basic feature of the model is that center vortices corresponding to magnetic flux J (in units of 2π/N) are composites of J elementary J=1 constituent vortices that come in N-1 types, with repulsion between like constituents and attraction between unlike constituents. The scalar-field theory is of a somewhat unusual type, involving N scalar fields φ

_{i}(one of which is eliminated) that can merge, dissociate, and recombine while conserving flux modN. The properties of these fields are deduced directly from the corresponding gauge-theory quantum solitons. Every vacuum Feynman graph of the theory corresponds to a real-space configuration of center vortices. We use qualitative features of this theory based on the vortex action to study the problem of k-string tensions (explicitly at large N, although large N is in no way a restriction on the model in general), whose solution is far from obvious in center-vortex language. We construct a simplified dynamical picture of constituent-vortex merging, dissociation, and recombination, which allows in principle for the determination of vortex areal densities and k-string tensions. This picture involves pointlike molecules made of constituent atoms in d=2 which combine and disassociate dynamically. These molecules and atoms are cross sections of vortices piercing a test plane; the vortices evolve in a Euclidean 'time' which is the location of the test plane along an axis perpendicular to the plane. A simple approximation to the molecular dynamics is compatible with k-string tensions that are linear in k for k<< N, as naively expectedPrimary Subject

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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[en] We investigate the implications of the nontrivial vacuum structure of little Higgs models. In particular, focusing on the littlest Higgs model, we demonstrate the existence of three types of topological defects. One is a global cosmic string that is truly topological. The second is more subtle; a semilocal cosmic string, which may be stable due to dynamical effects. The final defect is a Z

_{2}monopole solution with an unusual structure. We briefly discuss the possible cosmological consequences of such nonperturbative structures, although we note that these depend crucially on the fermionic content of the modelsPrimary Subject

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(c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

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