522 research outputs found
On the hierarchy of neutrino masses
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
and .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.
Precision W-boson and top-quark mass determinations at a muon collider
Precise determinations of the masses of the boson and of the top quark
could stringently test the radiative structure of the Standard Model (SM) or
provide evidence for new physics. We analyze the excellent prospects at a muon
collider for measuring and in the and threshold
regions. With an integrated luminosity of 10 (100) fb, the -boson
mass could be measured to a precision of 20 (6) MeV, and the top-quark mass to
a precision of 200 (70) MeV, provided that theoretical and experimental
systematics are understood. A measurement of MeV for fixed
would constrain a 100 GeV SM Higgs mass within about GeV, while
MeV for fixed would constrain to about GeV.Comment: 27 pages, 11 figures, postscript file available via anonymous
ftp://ucdhep.ucdavis.edu/han/mumu/mwmt.p
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