Sterile neutrino

A sterile neutrino is a hypothetical neutrino that does not interact via any of the fundamental interactions of the Standard Model except gravity. It is a right-handed neutrino or a left-handed anti-neutrino.

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Such a particle belongs to a singlet representation with respect to the strong interaction and the weak interaction and has zero weak hypercharge, zero weak isospin and zero electric charge. Sterile neutrinos would still interact via gravity, so if they are heavy enough, they could explain cold dark matter or warm dark matter. Current cosmological data bound the mass of the sterile neutrino to be less than 0.23 eV.^[1] In grand unification theories such as the Georgi-Glashow model they also interact via gauge interactions which are extremely suppressed at ordinary energies because their gauge boson is extremely massive.

In the Standard Model, sterile neutrinos may mix with ordinary neutrinos via a Dirac mass. The sterile neutrinos and ordinary neutrinos may also have Majorana masses. In certain models, both Dirac and Majorana masses are used in a seesaw mechanism, which drives ordinary neutrino masses down and makes the sterile neutrinos much heavier than the Standard Model interacting neutrinos. In some case the heavy neutrinos can be as heavy as the GUT scale (~10¹² GeV), but they could be even lighter than the weak gauge boson W and Z as in the so-called νMSM model where their masses are around GeV and keV.

On April 11, 2007, researchers at the MiniBooNE experiment at Fermilab announced that they had not found any evidence supporting the existence of the sterile neutrino.^[2] More recent results and analysis have provided some support for the existence of the sterile neutrino.[1]

The latest results, which show an excess of neutrino activity at the lower energies, have been interpreted as sterile neutrinos crossing the "bulk" of brane cosmology.

References

1. ^ S. Dodelson, A. Melchiorri and A. Slosar Phys.Rev.Lett. 97 (2006) 04301, http://xxx.lanl.gov/abs/astro-ph/0511500
2. ^ http://www-boone.fnal.gov/publicpages/First_Results.pdf

See also

• LSND
• MiniBooNE