If all three neutrino oscillation data were to be confirmed in the near future , it is probable that one might need a sterile neutrino , in addition to the three active ones .
This sterile neutrino , \nu _ { S } , would be very light with mass m _ { \nu _ { S } } \leq 1 eV or even with m _ { \nu _ { S } } \sim 10 ^ { -3 } eV according to some scenarios .
Why would it be so light ?
On another front , recent cosmological observations and analyses appear to indicate that the present universe is flat and accelerating , and that the present energy density is dominated by a “ dark variety ” , with \rho _ { V } \sim ( 10 ^ { -3 } eV ) ^ { 4 } .
Is it a constant ?
Is there a link between these apparently unrelated phenomena ?