Neutrino oscillations without neutrino masses or heavy mass scales: A Higher dimensional seesaw mechanism

Nov, 1998
17 pages
Published in:
  • Nucl.Phys.B 557 (1999) 25
e-Print:
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