Symmetry has a fairly new article on sterile neutrinos, explaining some of the basic ideas about what they are and why we’re interested in them. Measurements of the Z peak in e+/e- collisions at LEP showed that there are only 3 neutrinos, but there are some caveats to that. The measurements showing that there are 3 neutrinos really mean that there are 3 neutrinos that (1) have less than half the Z mass (91.2 GeV) and (2) interact with Standard Model particles via the weak force.
If we can instead add some “neutrinos” that don’t interact through the weak force, then there’s room for more neutrinos. One of the main ways people search for them is to find problems with the standard picture of 3-neutrino oscillations. If there are sterile neutrinos that mix with the three usual flavors (electron, muon, and tau), then maybe we can find evidence of neutrinos oscillating into sterile neutrinos. That is, regular neutrinos seemingly disappearing altogether rather than changing from one type to another.
Symmetry magazine has an ABCs of Particle Physics feature right now, which provides fun explanations of various topics in physics (with a focus on high energy physics). Everything is meant to be accessible to basically anyone. You can check it out here.
The ANTARES neutrino telescope has a new result looking for “secluded” dark matter, where dark matter annihilation is mediated through some new mediator that then decays into Standard Model particles. They claim that this can explain the high energy bump in the positron/electron ratio and can also still be a thermal relic from the Big Bang.
They look at several different channels, including one where the mediator actually lives long enough to reach Earth and decay in the atmosphere, and others where neutrinos in the final state are measured.
For this model, the result is actually stronger than direct detection experiments for spin-dependent interactions and is stronger at very high masses in the spin-independent channel. While this result isn’t particularly groundbreaking, the paper mentions that it is the first search of this kind for this type of dark matter, and I think the model, which I hadn’t heard much of previously, sounds quite interesting.
There’s a new white paper/review that just appeared on the arXiv about the possibility of keV-scale sterile neutrino dark matter. I haven’t read through it, but this is an interesting non-WIMP possibility for dark matter. Sterile neutrinos don’t interact at all with the Standard Model except maybe through neutrino oscillations, but if they have mass, they can still be a dark matter candidate if there’s a good production mechanism. Current dark matter experiments would generally be insensitive to this kind of dark matter, since the standard signal of low energy nuclear recoils would probably be disallowed, or at least heavily suppressed, but there are apparently still some paths toward finding sterile neutrino dark matter beyond just discovering keV-scale sterile neutrinos.
IceCube and Antares have looked for evidence of neutrino emission coincident with the gravitational wave signal seen by LIGO. They see no evidence of neutrinos being emitted by the gravitational wave source. That doesn’t mean there are no neutrinos, just that even if there are, not enough reached us to be able to see them. But, as the article points out, this means that gravitational wave and neutrino observatories can now work together to try to study rare astrophysical events.
Speaking of underground physics, Gizmodo has an article today on Snolab, with pictures of some of the facilities and a few detectors. Snolab is the deep underground lab in Sudbury, Ontario where a number of particle physics experiments are operating or are planned, such as SNO (and SNO+) and quite a few dark matter searches.
xkcd posted a particle physics related comic for Christmas this year.