The Road To New Physics Beyond Our Knowledge Might Pass Through Neutrinos

Currently, there are 100 trillion neutrinos flowing through you. Don’t worry though; they hardly interact with matter. In those occasional interactions, captured by some of the most sophisticated experiments on Earth, there are insights into some of the most complex events in the universe. As a new paper reports, we could be getting insights into reality itself.

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Neutrinos – you may have heard of them referred to as "ghost particles" – pass through everything because they are extremely light and have no electric charge. Still, they do have interactions with the electromagnetic force, something that is known as the neutrino charge radius. Neutrinos interact with electrons through the weak nuclear force.

According to the Standard Model of Particle Physics, the theory that underpins all the fundamental forces but gravity, there are very specific values for the charge radius and for the coupling value in the neutrino-electron weak force interaction. The Standard Model has limitations, but it has been such a successful theory that we have yet to find its flaws. This new, unified, high-precision test, using neutrino data from various sources, is the first to provide such a detailed test of the Standard Model predictions for neutrinos.

“By combining decades of data in a single, coherent framework, the work transforms a patchwork of individual experiments into a unified, high-precision test of the Standard Model,” co-author Dr Francesca Dordei from the Istituto Nazionale di Fisica Nucleare, told IFLScience.

The are three known types (also called flavors) of neutrinos: electron, muon, and tau neutrinos. The data was able to test the charge radii of all three. The team found no deviation between the standard model prediction and the experimental results. For the tau neutrino, the work provided the most stringent constraint on the charge radius from an experiment.

Things are more exciting when it comes to the weak force coupling. The scientists were able to reject several exotic interactions beyond the Standard Model, but revealed that there is a deviation from the prediction. The are two coupling parameters for the weak force, and they looked practically swapped in value compared to the standard model expectations.

“In our global fit, this swapped-coupling configuration is slightly favored, while the exact Standard Model point lies just outside the best-fit contour, so current data cannot rule out either picture. Future high-statistics dark matter and neutrino experiments should be able to tell which of the two islands is the correct one,” Dr Dordei told IFLScience.

Now, let’s not pop the champagne yet about this degenerate solution. It wouldn’t be the first time that an initial discrepancy disappears once more data has been collected. Still, this is a road map to where it might be good to look for possible new physics.

“The small tension associated with the degenerate solution is not a discovery claim, but a well-defined target: it tells experimentalists exactly what kind of improved neutrino and dark-matter data could transform today’s “ghost particles” into tomorrow’s cleanest probes of physics beyond the Standard Model,” Dr Dordei explained.

Thestudy is published in the journal Physical Review Letters.