OPERA’s measurement: theory’s speaking time

Einstein’s theory of relativity proven wrong, time travel finally possible, all our knowledge suddenly forced to change: superluminal neutrinos have triggered reactions from around the world. While the buzz spread, the theory community was following the usual scientific procedure, which implies understanding, thinking, reading, imagining, monitoring, reviewing and wondering: how could any theory account for OPERA’s result?


Last week, CERN theorists organised a workshop to discuss OPERA’s recent result. The workshop took place the whole morning of Friday 14 October and saw fruitful discussions among theorists, experimentalists, members of the OPERA Collaboration and members of the CERN community at large. The hot topic : assuming that OPERA’s result is confirmed by other experiments, is there any theory that could “accommodate” it? “We have reviewed a large part of the articles published in arXiv after OPERA made its result public,” says Ignatios Antoniadis, Head of CERN’s theory group. “After several discussions and a rich exchange of views, the participants in the workshop concluded that - currently - there is no consistent theoretical model that can accommodate the measurement.”

The main constraint on the existence of superluminal neutrinos as observed by OPERA comes from a paper published on 29 September by Andrew G. Cohen and Sheldon L. Glashow. “The argument presented by Cohen and Glashow is based on kinematics. It postulates that, while travelling from CERN to Gran Sasso, superluminal neutrinos lose some of their energy and emit electron-positron pairs. This phenomenon, not allowed if neutrinos have speeds slower than that of light, becomes possible if they travel faster,” explains Ignatios Antoniadis.

However, if neutrinos were to lose a considerable part of their energy, this would show up in OPERA’s plots…but it doesn’t: the energy distribution of neutrinos arriving at OPERA is very much as expected, without any depletion due to the phenomenon indicated by Cohen and Glashow. “For the time being, what we can say is that we need to keep on working on possible theoretical models which could account for the OPERA result without violating the constraints imposed by other experimental measurements. But Cohen and Glashow have already warned us that it will be a very difficult job,” says Christophe Grojean, a member of the theory group and one of the organisers of the workshop.

In other words, there’s no breaking news just yet - just a confirmation that, in the coming months, the OPERA result will continue to be under the scrutiny of the world's scientific community.

by CERN Bulletin