According to the Higgs mechanism in the Standard Model, particles in the vacuum acquire mass as they collide with the Higgs boson. Photons (γ) are massless because they do not interact with the Higgs boson. All particles, including electrons (e), muons (μ) and top quarks (t), change handedness when they collide with the Higgs boson; left-handed particles become right-handed and vice versa.
Experiments have shown that neutrinos (ν) are always left-handed. Since right-handed neutrinos do not exist in the Standard Model, the theory predicts that neutrinos can never acquire mass.
In one extension to the Standard Model, left- and right-handed neutrinos exist. These Dirac neutrinos acquire mass via the Higgs mechanism but right-handed neutrinos interact much more weakly than any other particles.
According to another extension of the Standard Model, extremely heavy right-handed neutrinos are created for a brief moment before they collide with the Higgs boson to produce light left-handed Majorana neutrinos.
Thus esults from several recent experiments provide indirect evidence in favor of the existence of a fourth generation neutrino. Such a neutrino with a mass m of about 50 GeV is compatible with current physical and astrophysical constraints and well motivated in the framework of superstring phenomenology.
If sufficiently stable, the existence of such a neutrino leads to a drastic change in Higgs boson physics. The dominant mode of Higgs boson decay is invisible and the branching ratios for the most promising modes of Higgs boson search are significantly reduced. And the mass of the Higgs boson is greater than 113.5 GeV if the neutrino mass is about 50 GeV.
-K A Solaman
Experiments have shown that neutrinos (ν) are always left-handed. Since right-handed neutrinos do not exist in the Standard Model, the theory predicts that neutrinos can never acquire mass.
In one extension to the Standard Model, left- and right-handed neutrinos exist. These Dirac neutrinos acquire mass via the Higgs mechanism but right-handed neutrinos interact much more weakly than any other particles.
According to another extension of the Standard Model, extremely heavy right-handed neutrinos are created for a brief moment before they collide with the Higgs boson to produce light left-handed Majorana neutrinos.
Thus esults from several recent experiments provide indirect evidence in favor of the existence of a fourth generation neutrino. Such a neutrino with a mass m of about 50 GeV is compatible with current physical and astrophysical constraints and well motivated in the framework of superstring phenomenology.
If sufficiently stable, the existence of such a neutrino leads to a drastic change in Higgs boson physics. The dominant mode of Higgs boson decay is invisible and the branching ratios for the most promising modes of Higgs boson search are significantly reduced. And the mass of the Higgs boson is greater than 113.5 GeV if the neutrino mass is about 50 GeV.
-K A Solaman
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