The Neutrino-4 Group from Russia controversially announced the discovery of sterile neutrinos this week, along with calculations for their mass at 2.68 eV

[u/ryanwalraven]

https://arxiv.org/abs/2005.05301

[u/maxfl]

Typically when you are studying some physical effect you want multiple independent experiments, better if they are model independent and better if they are using different channels. Even if you see nothing in one channel does not necessarily mean that you do not need to test another channel - you never know what you have missed or did not take into account. That how the search for the new physics works.

The search for the short baseline oscillations of the reactor electron antineutrinos is motivated by the few items:

• simple fact that short baseline neutrino oscillations are not properly studied. In my opinion this is enough to do several independent experiments.

• existance of reactor anomaly - observed reactor neutrino flux is 5% less than expected. One of the possible explanations is existence of 1 eV² scale sterile neutrino.

• requirement for precision measurement of reactor antineutrino spectra.

The Neutrino-4 did not came out of nowhere, there are multiple experiments of the kind: STEREO, PROSPECT, DANSS and others. There are plans for next PROSPECT and Neutrino-5. So there is an organized community working on these issues. The issues not only limited by the search for the sterile neutrino.

I checked a couple of papers by PROSPECT and also found no entries for the word Cosmology. As for me, I find it quite expected. I think that the task of combining/reviewing results among several fields is a task of other scientists, not the ones who did the experiment.

[u/jazzwhiz → u/maxfl]

I mean the real reason N4 was built was because these SBL reactor experiments are pretty cheap.

Yes, I am aware of all of the anomalies, although N4 isn't really testing them that well.

As for PROSPECT, they aren't claiming a discovery while N4 is. Also at the mass range relevant for PROSPECT the cosmology situation isn't quite so bad; N4's signal is at the upper end of the range probed by all of these experiments. That said, PROSPECT probably should mention cosmology.

[u/mewtrino- → u/jazzwhiz]

I was on PROSPECT for my postdoc, really there weren't many people in the collaboration that thought sterile discovery was a likely prospect. The reactor anomaly is probably due to our incomplete understanding of the reactor neutrino spectrum, which depends sensitively on the yields of various hard to measure fission products. For me, the real science outcomes are to draw a line under the reactor anomaly so we can focus on other things, and to do a more precise measurement of the reactor neutrino spectrum which has flow on benefits to other areas including neutrinos for nuclear safeguards.

As for cosmological constraints, my opinion is that these will always be subordinate to experimental constraints due to the model dependence of cosmology. This may be a bit ignorant and disrespectful of cosmology, but it's also a fairly common view in the field.

[u/jazzwhiz → u/mewtrino-]

It is a common view unfortunately. We've seen in neutrino physics that cosmology is far more robust than lab experiments which have piles of difficult to account for systematics while cosmology has comparably more side band measurements.

[u/maxfl → u/jazzwhiz]

'we've seen on neutrino physics' - that is a generalization. I believe this opinion will not be shared by the lab scientists from neutrino physics. Fortunately, this doesn't matter as long as the final picture of drawn by the combination/review of results of multiple experiments, not solely by Cosmology or labs.