715 research outputs found

    On the hierarchy of neutrino masses

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    We present a model of neutrino masses combining the seesaw mechanism and strong Dirac mass hierarchy and at the same time exhibiting a significantly reduced hierarchy at the level of active neutrino masses. The heavy Majorana masses are assumed to be degenerate. The suppression of the hierarchy is due to a symmetric and unitary operator R whose role is discussed. The model gives realistic mixing and mass spectrum. The mixing of atmospheric neutrinos is attributed to the charged lepton sector whereas the mixing of solar neutrinos is due to the neutrino sector. Small U_e3 is a consequence of the model. The masses of the active neutrinos are given by μ3Δm@2\mu_3\approx\sqrt{\Delta m_{@}^2} and μ1/μ2tan2θ\mu_1/\mu_2\approx \tan^2\theta_\odot.Comment: 12 pages; Talk presented by M. Jezabek at 'Supersymmetry and Brane Worlds,' Fifth European Meeting Planck 02, Kazimierz, Poland, May 25-29, 2002, to appear in Acta Phys. Polon.

    Scale Setting in Top Quark Decays

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    We compute the O(β0αs2)O(\beta_0 \alpha_s^2) QCD corrections to the Standard Model decay tW+bt\rightarrow W^+ b as well as the non standard decay tH+bt\rightarrow H^+ b. We then use our results to compute the BLM scale for these decays, and study the dependence of the BLM scale on the mass of the boson in the decay. We find that the BLM procedure gives extremely small scales when top decays into heavy bosons. When we try to improve the BLM scale by reexpressing rates as a functions of the top quark running mass, we find the BLM scale exhibits unnatural dependence on the boson mass, casting doubts on the applicability of the BLM procedure to these processes.Comment: Uses REVTEX, 9 pages, 4 EPS figures embedded with epsf.sty Some references and 1 figure added, conclusions slightly modified, numerical results unchanged. Version accepted for publication in Physics Letters
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