A minimal model with large extra dimensions to fit the neutrino data.pdf
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1 A MINIMAL MODEL WITH LARGE EXTRA DIMENSIONS TO FIT THE
NEUTRINO DATA
LING FU-SIN
Service de Physique The?orique
Universite? Libre de Bruxelles
Campus de la Plaine CP225
Bvd du Triomphe, 1050 Brussels, Belgium
The existence of large extra dimensions enables to explain very simply the various neutrino
suppression data. The flavour neutrinos, confined on the brane, are coupled to a ”bulk”
neutrino state, which is seen as an infinite tower of Kaluza-Klein states from the 4-dimensional
point of view. The oscillation of flavour neutrinos into these states can lead to a global and
sizable energy-independent suppression at large distances, which can be related to the solar
neutrino puzzle. 1
1 Introduction
The possibility of ”large extra dimensions”, i.e. with (at least) one compactification radius close
to the current validity limit of Newton’s law of gravitation (～ 1mm), raises considerable interest.
One reason is that it could solve the ”so-called” hierarchy problem 2 by providing us with a new
fundamental energy scale M? around 1 TeV. The discrepancy between the apparent huge value
of the Planck scale and the weak scale then results from the fact that extra dimensions remain
”hidden” at low energies for all interactions except gravitation. From the relation
M2P lanck = Vn ·Mn+2?
we see that at least 2 extra dimensions are needed (n ≥ 2) to avoid deviations from Newton’s
law.
Another reason is that it can bring some new physics just ”around the corner”, at energies
as low as 1 TeV. In particular, neutrino physics is a ideal area to study new theories. While
particles belonging to the Standard Model (SM) are required to be confined on the usual four
dimensional spacetime (the 3-brane with thickness ～ 1 TeV ?1), sterile neutrinos, which do not
experience any of the gauge interactions, can propagate in the 4+n dimensional spacetime as
well as gravitons, and turn to be an efficient tool to probe the ”bulk” of
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