With the Higgs boson having been successfully discovered by CERN, neutrinos are now of great interest in the puzzle of why matter outbalanced antimatter at the beginning of the universe, a question strongly associated with the Higgs. Fundamentally, at the time of the primordial soup, matter and antimatter ought to have existed in equal parts. Had they done so equally, they would have annihilated each other resulting in a universe that we could never ponder because we could not have come to be: people and all other objects are comprised of matter. This being the case, at some point and for some reason, matter outweighed antimatter, and baryonic matter came to be.
Neutrinos were originally thought to be weightless but when the CERN-Gran Sasso experiment called OPERA recorded the oscillation of a muon-neutrino into a tau-neutrino as it morphed in mid-flight from CERN’s neutrino cannon to Gran Sasso’s bricks of lead plated photographic emulsion films, neutrino theory had to be adjusted to allow for neutrinos with mass. Still, the theoretically assigned mass was very low at 0.06 electron volt. Mass is required for an oscillation, which is a morph from one neutrino flavor to another, and each neutrino must carry the mass of all three flavors or the oscillation could not occur. Essentially, then, the oscillation from one flavor to another is an oscillation from one mass state to another mass state, with all three mass states theorized to be carried by each neutrino. Until recently, the only oscillations recorded have been from muon, an easy to manufacture neutrino, to tau, though the new Fermilab NOvA experiment, shooting muon neutrinos from Illinois to Minnesota, recorded oscillations of muon to electron neutrinos early in 2014. A new development reported in February 2014 has raised two interesting possibilities for neutrinos.
Heavier Mass for Neutrinos
The first possibility is that they may be heavier, have more mass, than originally theorized, with a mass of 0.32 electron volt rather than 0.06 eV. The frequency of oscillation from one flavor to another is, therefore, related to the mass of the neutrinos and will provide a beginning point for identifying their individual masses. If 0.32 eV is the final mass range, then that will indicate that their masses are nearly equal, which will be an unexpected result leading to more questions about the mechanism of their masses. One possible idea about the mechanism is that something other than the Higgs boson gives neutrinos their mass (Higgs boson was discovered by CERN in 2012 and gained Peter Higgs and Francois Englert the Nobel Prize in Physics in 2013).
Fourth Flavor of Neutrino
The second possibility is that there is a fourth flavor of neutrino. This theorized hot, fast fourth neutrino flavor is called a “sterile” neutrino. A fourth neutrino would be heralded as new physics that would contradict the present Standard Model theory of everything since there is no place in the Model for an additional neutrino. Two characteristics of the sterile neutrino are that it would not oscillate (not change to other neutrino flavors, therefore carry only its own mass) and it would interact even less with matter than the first three flavors do (muon, tau, electron), and these interact so weakly with matter that they are called WIMPs (weakly interacting massive particles) and pass right through the human body unnoticed on a regular, daily basis.
CMB-Galaxy Scatter Imbalance
These two new possibilities arose because of the imbalance discovered between the comic microwave background (CMB) and the spread of the clusters of galaxies scattered around the universe. It has been shown that the imbalance between the CMB and the scattered galaxy clusters could be evened out if neutrinos have more mass than previously believed, which would add to the overall mass of clustering galaxies and effect their clustering, a clustering that is significantly lower than expected, and if a portion of the total neutrino mass–albeit light–were associated with dark matter.
Hindered Galaxy Clustering
The tension, or discrepancy, between the two (CMB and galaxy clustering) could be explained if neutrinos somehow hindered galaxy cluster spread. This might have occurred is if sterile neutrinos (which do not oscillate) comprise part of dark matter. It is dark matter that accounts for up to 85 percent of the mass of the universe and that provides the substance within which galaxies are formed and by which they are held in shape. It is theorized that in the hot, dense early moments of the formation of the universe, neutrinos moved relativistically at the speed of light (they now move just under the speed of light as shown by the CERN-Gran Sasso OPERA experiment). It is theorized that a universal threshold of heat and density was crossed and neutrinos slowed and cooled somewhat. Then, the three WIMP neutrinos began interacting–albeit weakly–with matter, tipping the balance of, the mass of, the universe toward matter and away from antimatter, while sterile neutrinos, having an even weaker interaction with matter, interacted instead with dark matter (matter that is not visible in any light register of the spectrum). When considering hindrance, the weak interaction of oscillating neutrinos with the spread of clustering galaxies–with the resultant addition of light mass–and the weak interaction of sterile neutrinos with dark matter would both have hindered the clustering of galaxies enough to explain the imbalance between the CMB and the spread of galaxy clusters. [The CMB is the continuing microwave radiation vibrations of the early moments of the universe’s formation and would accord with what was formed (to illustrate, the acoustic vibrations of a falling tree accord with its size and its nesting birds and squirrels.]
Kathryn Jepsen. “Watch the next big neutrino experiment come together.” Symmetry. 30 January 2014.
Clara Moskowitz. “Cosmic Mismatch Hints at the Existence of a “Sterile” Neutrino.” Scientific American. 20 February 2014.
Adrian Cho. “New Neutrino May Have Heated Baby Universe.” Science, Vol 343. 21 February 2014.