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Saul-Paul Sirag wrote on 11-18-11

Hi Jack,

In case you missed it, Cohen and Glashow deny the validity of the FTL OPERA neutrinos.
They base their analysis on the absence of a kind of Cerenkov effect.

I'll attach a description of Cohen & Glashow's paper here:

"What Cohen and Glashow did last week was to generalize this idea to point out a new physical phenomenon (new at least to me) and use it to argue that OPERA’s result is self-inconsistent. They argue that the very effect of fasterthan-light travel that OPERA claims to observe would have caused distortions in its neutrino beam that clearly were not observed. Moreover, Cohen and Glashow also pointed out that at least two other experiments studying higher energy neutrinos put even stronger constraints on the possibility of anything similar to what OPERA observed. ...

What Cohen and Glashow did last week was to generalize this idea to point out a new physical phenomenon (new at least to me) and use it to argue that OPERA’s result is self-inconsistent. They argue that the very effect of faster-than-light travel that OPERA claims to observe would have caused distortions in its neutrino
beam that clearly were not observed. Moreover, Cohen and Glashow also pointed out that at least two other experiments studying higher energy neutrinos put even stronger constraints on the possibility of anything similar to what OPERA observed. ...

You might wonder whether the supernova neutrinos are of one type, and might have one speed, while those at OPERA might be a different neutrino-type and travel at a different speed. This possibility, as Coleman and Glashow pointed out in their papers from the 1990s, is excluded by the various experiments on neutrino oscillations, whose internal self-consistency would be badly broken if different types of neutrinos traveled at speeds as different as would be required to reconcile the supernova neutrinos with OPERA’s neutrinos. In fact, the constraints on the differences between the speeds of different neutrino types is at the level of ten parts per billion trillion! We can forget about that possibility being important. From these two paragraphs we conclude that if OPERA is right, the speed of all three types of neutrinos must increase with energy, differing from light speed by a few parts per billion or less for neutrinos with 0.01-0.04 GeV, and differing at a few parts per hundred thousand for OPERA’s neutrinos, with 10-40 GeV of energy. ...

The basic idea is that a neutrino that travels fast enough can potentially lose energy by emitting a particle and a corresponding antiparticle through effects of the weak nuclear force. Specifically, if a neutrino could travel faster than electrons could travel, then with sufficient energy the neutrino could emit an electron and a positron. Well, are the OPERA neutrinos traveling faster than electrons can travel? Yes, because of what we know about electrons from Cerenkov radiation. We know that electrons at energies below a TeV cannot travel faster than the speed of light in vacuum by more than one part in a thousand trillion, because if they could, they would Cerenkov radiate even in vacuum. In this case we would never observe the high-energy electrons that we do in fact see in experiments. And therefore, if neutrinos travel faster than light by a few parts per hundred thousand, then they likewise travel faster than the maximum speed of electrons by about the same amount. It follows that for sufficiently high energy, neutrinos can spit off an electron-positron pair."

Of Particular Significance
Conversations About Science with Theoretical Physicist Matt Strassler

There are theories in which the speed of light changes with energy from vacuum dispersion caused by the quantization of space-time and non-commutativity (A. Connes) of spacetime as I recall. These are extensions of c-number relativity not fundamental violations of it.

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