2,046,354 research outputs found

    Majorana neutrino versus Dirac neutrino in e+eW+W{\rm e}^{+}{\rm e}^{-} \to {\rm W}^{+}{\rm W}^{-} through radiative corrections

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    Radiative corrections to e+e ⁣W+W{\rm e}^{+}{\rm e}^{-}\! \rightarrow {\rm W}^{+}{\rm W}^{-} from Majorana neutrinos are studied in the context of the see-saw mechanism. Focusing on the effects of the fourth generation neutrinos, we calculate W-pair form factors, the differential cross sections and the forward-backward asymmetries for the polarized electrons at one-loop level. The behaviour of the form factors at the threshold of Majorana particle pair productions is found to differ from that of Dirac particle pair productions. In the cross section for unpolarized electrons, the radiative corrections, depending on the mass parameters of the see-saw mechanism, are found to be 0.5%\sim 0.5\% at the energy range of the LEP200 and the next generation linear colliders.Comment: 10 pages, Latex, 4 figures(no included, available on request

    Transmission Electron Study of Heteroepitaxial Growth in the BiSrCaCuO System

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    Films of Bi2\rm _2Sr2\rm _2CaCu2\rm _2O8\rm _8 and Bi2\rm _2Sr2\rm _2CuO6\rm _6 have been grown using Atomic-Layer-by-Layer Molecular Beam Epitaxy (ALL-MBE) on lattice-matched substrates. These materials have been combined with layers of closely-related metastable compounds like Bi2\rm _2Sr2\rm _2Ca7\rm _7Cu8\rm _8O20\rm _{20} (2278) and rare-earth-doped compounds like Bi2\rm _2Sr2\rm _2Dyx\rm _xCa1x\rm _{1-x}Cu2\rm _2O8\rm _8 (Dy:2212) to form heterostructures with unique superconducting properties, including superconductor/insulator multilayers and tunnel junctions. Transmission electron microscopy (TEM) has been used to study the morphology and microstructure of these heterostructures. These TEM studies shed light on the physical properties of the films, and give insight into the growth mode of highly anisotropic solids like Bi2\rm _2Sr2\rm _2CaCu2\rm _2O8\rm _8.Comment: 17 pages, submitted to J. Materials Research. Email to [email protected] if you want to receive copies of the figure

    The Charge Form Factor of the Neutron at Low Momentum Transfer from the 2H(e,en)p^{2}\vec{\rm H}(\vec{\rm e},{\rm e}'{\rm n}){\rm p} Reaction

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    We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMnG^{n}_{E}/G^{n}_{M} was extracted from the beam-target vector asymmetry AedVA_{ed}^{V} at four-momentum transfers Q2=0.14Q^{2}=0.14, 0.20, 0.29 and 0.42 (GeV/c)2^{2}.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Let

    Possible existence of Ep-Lp and Ep-Eiso correlations for Short Gamma-Ray Bursts with a factor 5 to 100 dimmer than those for Long Gamma-Ray Bursts

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    We analyzed correlations among the rest frame spectral peak energy EpE_{\rm p}, the observed frame 64ms peak isotropic luminosity LpL_{\rm p} and the isotropic energy EisoE_{\rm iso} for 13 Short Gamma Ray Burst (SGRB) candidates having the measured redshift zz, T90obs/(1+z)<2T_{\rm 90}^{\rm obs}/(1+z)<2 sec and well determined spectral parameters. A SGRB candidate is regarded as a misguided SGRB if it is located in the 3-σint\sigma_{\rm int} dispersion region from the best-fit function of the EpE_{\rm p}--EisoE_{\rm iso} correlation for Long GRBs (LGRBs) while the others are regarded as secure SGRBs possibly from compact star mergers. Using 8 secure SGRBs out of 13 SGRB candidates, we tested whether EpE_{\rm p}--EisoE_{\rm iso} and EpE_{\rm p}--LpL_{\rm p} correlations exist for SGRBs. We found that EpE_{\rm p}--EisoE_{\rm iso} correlation for SGRBs(Eiso=1051.42±0.15ergs1(Ep/774.5keV)1.58±0.28E_{\rm iso} =10^{51.42 \pm 0.15}{\rm erg s^{-1}} ({E_{\rm p}}/{\rm 774.5 keV})^{1.58 \pm 0.28}) seems to exist with the correlation coefficeint r=0.91r=0.91 and chance probability p=1.5×103p=1.5\times10^{-3}. We found also that the EpE_{\rm p}--LpL_{\rm p} correlation for SGRBs(Lp=1052.29±0.066ergs1(Ep/774.5keV)1.59±0.11L_{\rm p} = 10^{52.29 \pm 0.066}{\rm erg s^{-1}} ({E_{\rm p}}/{\rm 774.5 keV})^{1.59 \pm 0.11}) is tighter than EpE_{\rm p}--EisoE_{\rm iso} correlation since r=0.98r=0.98 and p=1.5×105p=1.5\times10^{-5}. Both correlations for SGRBs are dimmer than those of LGRBs for the same EpE_{\rm p} by factors \sim100 (EpE_{\rm p}--EisoE_{\rm iso}) and \sim 5(EpE_{\rm p}--LpL_{\rm p}). Applying the tighter EpE_{\rm p}--LpL_{\rm p} correlation for SGRBs to 71 bright BATSE SGRBs, we found that pseudo redshift zz ranges from 0.097 to 2.258 with the mean of 1.05. The redshifts of SGRBs apparently cluster at lower redshift than those of LGRBs (2.2\sim 2.2 ), which supports the merger scenario of SGRBs.Comment: 8 pages, 6 figures, Accepted for publication in MNRA

    Kernel solutions of the Kostant operator on eight-dimensional quotient spaces

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    After introducing the generators and irreducible representations of the su(5){\rm su}(5) and so(6){\rm so}(6) Lie algebras in terms of the Schwinger's scillators, the general kernel solutions of the Kostant operators on eight-dimensional quotient spaces su(5)/su(4)×u(1){\rm su}(5)/{\rm su}(4)\times {\rm u}(1) and so(6)/so(4)×so(2){\rm so}(6)/{\rm so}(4)\times {\rm so}(2) are derived in terms of the diagonal subalgebras su(4)×u(1){\rm su}(4)\times {\rm u}(1) and so(4)×so(2){\rm so}(4)\times {\rm so}(2), respectively.Comment: 13 pages. Typos correcte

    Theory Morphisms in Church's Type Theory with Quotation and Evaluation

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    CTTqe{\rm CTT}_{\rm qe} is a version of Church's type theory with global quotation and evaluation operators that is engineered to reason about the interplay of syntax and semantics and to formalize syntax-based mathematical algorithms. CTTuqe{\rm CTT}_{\rm uqe} is a variant of CTTqe{\rm CTT}_{\rm qe} that admits undefined expressions, partial functions, and multiple base types of individuals. It is better suited than CTTqe{\rm CTT}_{\rm qe} as a logic for building networks of theories connected by theory morphisms. This paper presents the syntax and semantics of CTTuqe{\rm CTT}_{\rm uqe}, defines a notion of a theory morphism from one CTTuqe{\rm CTT}_{\rm uqe} theory to another, and gives two simple examples that illustrate the use of theory morphisms in CTTuqe{\rm CTT}_{\rm uqe}.Comment: 17 page

    Lattice effects in the La2x_{\rm 2-x}Srx_{\rm x}CuO4_{\rm 4} compounds

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    Systematic Raman studies on several cuprates (YBa2_{\rm 2}Cu3_{\rm 3}Ox_{\rm x}, YBa2_{\rm 2}Cu4_{\rm 4}O8_{\rm 8} or Bi2_{\rm 2}Sr2_{\rm 2}CaCu2_{\rm 2}O8_{\rm 8}) have shown that at optimal doping the compounds are at the edge of lattice instability; once this level is exceeded, by means of doping or applying external hydrostatic pressure, the changes in the transition temperature are accompanied by spectral modifications. There are strong indications that the reduction in Tc_{\rm c} is correlated with a separation into nanoscale phases, which involve the oxygen atoms of the CuO2_{\rm 2} planes. In this work, modifications with doping in the Raman spectra of the La2x_{\rm 2-x}Srx_{\rm x}CuO4_{\rm 4} compound are presented, which show that spin or charge ordering is coupled with lattice distortions in the whole doping region.Comment: 6 pages, 6 figure