Neutrinos are one of the only particles known to violate the Standard Model of particle physics. Neutrinos do this because of flavor oscillation. Neutrinos can be made as one type, or flavor, and then spontaneously change as they propagate. This effect has been observed to occur, however the Standard Model doesn’t predict it. This makes neutrinos excellent particles to study to learn more about the physics needed to improve the Standard Model.
Core-collapse supernovae provide an environment for any nonstandard interactions (NSI) to be observed in the neutrino signal. In the dense cores of supernovae, neutrinos are coupled to the matter, but they quickly decouple as the density drops. This allows neutrinos to carry information directly from these dense cores out where it can be observed. The interactions neutrinos undergo in this region could cause flavor mixing that would be detected in our detectors on earth. By understanding such a future neutrino signal we could then decrypt the types of interactions that were present.
My work used NSI between neutrinos and the most common elementary particles: electrons, up quarks, and down quarks. Without detailing the specific interactions, I explored a slice of the parameter space defined by the strength of those interactions to observe the effects on the flavor oscillations. The results of this parameter study is shown in the following plot where the colors correspond to a different observed behavior in the neutrino history.
Point A
For small values of both NSI parameters used, we saw two prominent effects. First, even at these small values of the NSI parameters, we find an inner or I-resonance that causes 100% conversion of neutrino flavors at 10s of kilometers above the neutrinosphere surface. This flavor conversion sets up a reversal of the behavior normally associated with each hierarchy with a bipolar/nutation collective effect observed in the Normal Hierarchy and no such behavior in the Inverted Hierarchy.
Point B
As the values of the NSI parameters increase we observe the probabilities begin to show the effects of a Matter Neutrino Resonance (MNR) first discovered in the context of merger-disk scenarios at NC State by Dr. Gail McLaughlin‘s research group. This type of resonance was not expected to occur without an overabundance of anti-neutrinos; however the I-resonance creates similar conditions allowing for a cancellation of the matter and neutrino-neutrino interaction terms of the Hamiltonian.
Point C
The location and width of the I-resonance is proportional to the two NSI parameters. As these get larger the resonance moves to larger radii and gets wider. Eventually, this causes the I-resonance to overlap with the onset of an MNR as happens at point C. This has interesting effects that are different between the two hierarchies. In the Normal Hierarchy, the MNR dominates and begins from a point before the I resonance has fully converted neutrinos. In the inverted hierarchy, the onset of the MNR is delayed until the I-resonance fully converts. If this effect is observed, it could provide key clues about the mass ordering of the neutrino hierarchy.
Point D
Continuing to increase the NSI parameters will eventually cause the I-resonance and MNR to overlap too much and completely disrupt the MNR. This returns the behavior of the signal back to the same as at point A with an I resonance at a few 10s of kilometers and bipolar collective effects after that.
Point E
This represents a region of chaotic effects. Such a large value for the neutron coupling with a small off-diagonal NSI contribution means that the I-resonance, MNR, and bipolar effects are all overlapping without fully disrupting each other. Small changes in the parameters here can have a large effect on the survival probabilities as different resonances become more and less dominant.
Point F
In the soft blue and purple regions that surround point F. At this point the I resonance has moved so far out that it disrupts the normal MSW H-resonance that occurs at thousands of kilometers. This effectively inverts the signals for neutrinos and anti-neutrinos in the two different hierarchies.
Charles J. Stapleford 