21,192 research outputs found

    Isospin breaking in pion-nucleon scattering at threshold by radiative processes

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    We investigate the dispersive contribution by radiative processes such as (pi- proton to neutron gamma) and (pi- proton to Delta gamma) to the pion-nucleon scattering lengths of charged pions in the heavy baryon limit. They give a large isospin violating contribution in the corresponding isoscalar scattering length, but only a small violation in the isovector one. These terms contribute 6.3(3)% to the 1s level shift of pionic hydrogen and give a chiral constant F_pi^2f_1=-25.8(8) MeV.Comment: 9 pages with 1 figur

    A model of gravitation with global U(1)-symmetry

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    It is shown that an embedding of the general relativity 44-space into a flat 1212-space gives a model of gravitation with the global U(1)U(1)-symmetry and the discrete D1D_{1}-one. The last one may be transformed into the SU(2)SU(2)-symmetry of the unified model, and the demand of independence of U(1)U(1)- and SU(2)SU(2)-transformations leads to the estimate sin2θmin=0,20\sin^{2}\theta_{min}=0,20 where θmin\theta_{min} is an analog of the Weinberg angle of the standard model.Comment: 7 page
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