Tuesday, October 4, 2011

More faster-than-light neutrino speculation

Continuing perusal of the arxiv.org papers,

In http://arxiv.org/pdf/1109.5917v1, say that tachyonic neutrinos are positively ruled out because it would also require a violation of the conservation of energy, "a tachyonic interpretation is not only hardly reconciled with OPERA data on energy dependence, but that it clashes with neutrino production from pion and with neutrino oscillations."  They further explore some papers from the 90s by Coleman and Glashow that suggest test for the Lorentz equations in cosmic rays and accelerators.  Their basic suggestion is that neutrinos have their own limiting velocity that is different from (and possibly greater than) the speed of light.  This hypothesis is contradicted by neutrino oscillation experiments.  Oh well.

In http://arxiv.org/PS_cache/arxiv/pdf/1109/1109.6641v1.pdf, the authors work very hard to reconcile the SN1987a neutrino results with the OPERA results.  To review, the supernova neutrinos arrived 4 hours earlier than the light from the supernova (over 160,000 years--2 parts in a billion deviation).  Of course, the OPERA neutrinos are faster than light by 50 parts in a million.  Their main assertion is, obviously, neutrinos travel faster in Earth than in inter-galactic space.  OK.  Right.

In http://arxiv.org/PS_cache/arxiv/pdf/1109/1109.6282v1.pdf, the authors suggest, "the existence of light sterile neutrinos which can propagate in a higher dimensional bulk and achieve apparent superluminal velocities when measured by an observer confined to the 4D brane of the standard model."  That is, they find a shortcut in the extra dimensions (needed by many versions of String Theory) of space.  But only "sterile" neutrinos can do this, as "fertile" ("dirty"?) neutrinos are confined to be in our regular old four-dimensional space.  But OPERA measures muon neutrinos--they aren't sterile.

In "Superluminal Neutrinos without Revolution" by Susan Gardner of the University of Kentucky, she speculates that neutrinos are unique in that they do not interact with the "dark universe" like the rest of the particles.  Regular particles are slowed down by this interaction.

None of these are at all satisfying.

What are people speculating is the reason for the Faster-than-light neutrinos?

I have done a simple survey of papers from arxiv.org that match the search criteria "neutrino" and "opera".  At this moment, there are over 100 such papers.  Here is a summary.

In "New Constraints on Neutrino Velocities" by Andrew G. Cohen and Sheldon L. Glashow of Boston University (http://arxiv.org/pdf/1109.6562), they claim "that such superluminal neutrinos would lose energy rapidly via the bremsstrahlung of electron-positron pairs" and thus refute this discovery.

Walter Winter of Institut fur Theoretische Physik und Astrophysik, Universitat Wurzburg, suggests that maybe not all of the neutrinos are faster than light.  But he says that this does not particularly lead to any "reasonable" explanation.

Markus G. Kuhn of the Computer Laboratory at the University of Cambridge calculates that the Coriolis Effect of the south-eastward travelling neutrinos would only account for 2.2 nsec.  Oh well.

Shi-Yuan Li, School of Physics, Shandong University, Jinan, PRC says that all OPERA has done is "measured the phase speed of the neutrino wave function."  How boring.  He says, "velocity is too complex and case-dependent, generally can not be taken as basic observable related to some kind of space-time symmetry, but as a quantity defined by others, depending on the concrete cases."  Tell that to the police officer the next time you are pulled over for speeding.

E. Canessa, Science & Technology Collaborium, Italy, says "We pinpoint how a subatomic particle with non-zero mass may attain, in principle, velocities faster-than-light by travelling in helical motion in the limit of very large momentum."  He does a lot of hand-waving (and shows very little of his work) to conclude that the apparent velocity of a helically-moving neutrino is equal to the opening angle (in radians) of the helix, which can be greater than one.

Rafael S. Torrealba, Departamento de F´ısica.Universidad Centro Occidental ”Lisandro Alvarado”, suggest that "These puzzling result could be explained by stimulated emission of neutrinos in the decay tunnel, in close analogy with the amplification of a LASER pulse."  I don't get it.  I don't even know where this guy is (this seems to be Spanish, but maybe it is Italian).

G. Henri, Institut de Planetologie et d'Astrophysique de Grenoble (IPAG), Grenoble, France says, "it is enough that the beam composition varies during the leading and the trailing edges to explain an apparent time shift in the detected neutrinos."  I think the OPERA folks addressed this particular problem quite well.

Jerrold Franklin of the Department of Physics at Temple (Philadelphia, PA), says "The superluminal propagation of neutrinos observed by the OPERA collaboration is shown to be due to an imaginary ‘optical’ potential for the attenuation of the neutrino beam in passage through the Earth."  The heart of this one is the assumption that the mass of the neutrino has an imaginary component related to its attenuation.  He goes on to say that this accounts for the fact that the neutrinos in the SN1987a arrived in coincidence with the light from that event--there is no attenuation in space.  I don't buy it.