"Such a massive neutrino doesn't fit with anything theoretically," Dr. Bahcall said.

We have not considered the case of three equally massive neutrinos because of the strong limits on the electron neutrino mass.

The new research, Dr. Primack said, could mean that massive neutrinos could account for 10 to 20 percent of the theorized mass density of the universe.

A possible resolution may be in the form of massive (around 2eV) neutrinos.

Some of the dark matter is massive neutrinos, whose masses are being measured in a number of experiments.

Still other theories conjecture that the universe is full of exotic, undetected particles with such names as super-symmetric photinos, massive neutrinos, magnetic monopoles and "wimps."

Thus oscillating neutrinos must have mass; but massive neutrinos need not oscillate.

Additionally, free-streaming massive neutrinos suppress the growth of structure on small scales.

In particular, an interesting new model should address questions left unanswered in the Standard Model which has, including three massive neutrinos, 28 free parameters.

These pieces of additional physics include relaxing or removing the assumption of homogeneity, or inserting new particles such as massive neutrinos.