Neutrino oscillations without neutrino masses or heavy mass scales: A Higher dimensional seesaw mechanism
Nov, 199817 pages
Published in:
- Nucl.Phys.B 557 (1999) 25
e-Print:
- hep-ph/9811428 [hep-ph]
Report number:
- CERN-TH-98-370
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Abstract:
Recent theoretical developments have shown that extra spacetime dimensions can lower the fundamental GUT, Planck, and string scales. However, recent evidence for neutrino oscillations suggests the existence of light non-zero neutrino masses, which in turn suggests the need for a heavy mass scale via the seesaw mechanism. In this paper, we make several observations in this regard. First, we point out that allowing the right-handed neutrino to experience extra spacetime dimensions naturally permits the left-handed neutrino mass to be power-law suppressed relative to the masses of the other fermions. This occurs due to the power-law running of the neutrino Yukawa couplings, and therefore does not require a heavy scale for the right-handed neutrino. Second, we show that a higher-dimensional analogue of the seesaw mechanism may also be capable of generating naturally light neutrino masses without the introduction of a heavy mass scale. Third, we show that such a higher-dimensional seesaw mechanism may even be able to explain neutrino oscillations without neutrino masses, with oscillations induced indirectly via the masses of the Kaluza-Klein states. Fourth, we point out that even when higher-dimensional right-handed neutrinos are given a bare Majorana mass, the higher-dimensional seesaw mechanism surprisingly replaces this mass scale with the radius scale of the extra dimensions. Finally, we also discuss a possible new mechanism for inducing lepton-number violation by shifting the positions of D-branes in Type I string theory.Note:
- 36 pages, LaTeX, 6 figures. Substantially enlarged; previous mechanisms strengthened and generalized; many new results added Report-no: CERN-TH/98-370 (November 1998)
- neutrino: oscillation
- neutrino: mass
- neutrino: massless
- neutrino: mixing angle
- neutrino: right-handed
- neutrino: left-handed
- Kaluza-Klein model
- space-time: higher-dimensional
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