It looks like new evidence is slowly mounting in favor of some extra, 'sterile' families of neutrinos, coming from some hitherto uninvolved in the issue corners, and supporting some earlier results, which were also commented on in this blog.
This time the experimental approach is rather different as the observed neutrinos are generated in the core of the nuclear plants and thus governed by rather murky rules of the nuclear physics. This is quite in contrast, well in a negative sense of it, with neutrino accelerator experiments, such as miniBooNE. As however argued here new modeling approaches combined with better experimental data seem provide a solid framework within which to have a look back at some of the past nuclear reactor based neutrino experiments performed over the last 20-30 years or so. The re-analysis of their data seems to indicate a deficit of neutrinos at the shortest distance from the source (on order of tens of meters) as compared to what is thought to be produced in the reactor. Yet again neutrino oscillations seem to provide a most natural and convenient explanation for such a phenomenon. The short oscillation length implied by this results calls for high neutrino mass difference and thus, given all the other constraints from atmospheric and solar neutrino observations, suggests an existence of a yet another neutrino species, immune to all known forces - but gravity - and just there to conveniently let other, 'normal' neutrino species to transform into it. Too much to ask for ?! Well, feels this way to be sure, but who we are to argue with the facts ...
This time just one extra family is what is only needed. A sign of a contradiction with the older results ?! Not really. More can probably do as well. And moreover, the gossip has it that the two families as apparently asked for by the miniBooNE and LSND are not anymore a must and, conveniently so, one will do as well !
In all of that only cosmology seems to be at odds. And in fact nothing less but one of its central results based on the light elements observations and its interpretation within a framework of the Big Bang Nucleosynthesis (BBN), which, as has been known for a few decades now, limits the number of neutrino species to ... three. That on its own could be bypassed if some non-thermal distribution for 4th family of neutrinos is adopted, but then the new results from WMAP satellite suggesting that the preferred number of the neutrino species is indeed four, would have to be just a fluke ... But then again the gossip has it ... Well I'll check that out before writing that here though ... (*)
Lo and behold, no more any need to be old to partake in excitements of neutrino physics, eh ?!
(*) 5 hours later ...
And check I did ! So it does seem that the Big Bang Nucleosynthesis constraints on a number of neutrinos have gone up and now four is well within the uncertainties !
The relevant papers can be found here and here. The reason behind this, well near-revolution, recall the early success of the BBN was (is ?!) recognized as one of the founding pillars of the Standard Big Bang Cosmology, are the revised constraints on the 4He number densities, which have been recently updated and found to be 2σ higher than the old ones ... If that holds on, that will be yet another example of CMB leading the way in revising an area of "standard" science ... Quite amazing indeed !
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