Neutrinos are neutral elementary particles born in the radioactive decay of other particles. The known "flavors" of neutrinos are the neutral counterparts of electrons and their heavier cousins, muons and taus. Regardless of a neutrino's original flavor, the particles constantly flip from one type to another in a phenomenon called "neutrino flavor oscillation."
An electron neutrino might become a muon neutrino, and then later an electron neutrino again. Scientists previously believed three flavors of neutrino exist. In this Mini Booster Neutrino Experiment, dubbed MiniBooNE, researchers detected more oscillations than would be possible if there were only three flavors.
"These results imply that there are either new particles or forces we had not previously imagined," said Byron Roe, professor emeritus in the University of Michigan's Department of Physics, and an author of a paper on the results newly published online in Physical Review Letters.
"The simplest explanation involves adding new neutrino-like particles, or sterile neutrinos, which do not have the normal weak interactions." . . .
The paper is called "Event Excess in the MiniBooNE Search for ν̅ μ→ν̅ e Oscillations."
See also reports here, and here, and here. News release from Fermilab here.
If the mass is right, this could be a strong dark matter candidate.
CP violations are also observed, echoing CP violations in neutrinos suggested earlier this year in another experiment (previously blogged here).
Many versions of the fundamental physical theories, including Supersymmetry and String Theory (which implies some sort of Supersymmetry) theoretically conclude that there must be three and only three flavors of particles. If there are indeed four flavors of neutrinos, this would contradict these theories.
In less experimental physics, meanwhile, there is discussion of a Higgsless standard model possiblity.