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Abstract: If there are scalar particles of small or moderate mass coupled very weaklyto Dirac neutrinos, in a minimal way, then neutrino-anti-neutrino clouds ofsufficient number density can experience an instability in which helicities aresuddenly reversed. The predicted collective evolution is many orders ofmagnitude faster than given by cross-section calculations. The instabilitiesare the analogue of the ``flavor-angle- instabilities enabled by the Zexchange force that may drive very rapid flavor exchange among the neutrinosthat emerge from a supernova. These exchanges do require a tiny seed inaddition to the scalar couplings, but the transition time is proportional tothe negative of the logarithm of the seed strength, so that the size of thisparameter is comparatively unimportant. For our actual estimates we use a tinynon-conservation of leptons; an alternative would be a neutrino magnetic momentin a small magnetic field. The possibility of a quantum fluctuation as a seedis also discussed. Operating in the mode of putting limits on the couplingconstant of the scalar field, for the most minimal coupling scheme, withindependent couplings to all three $ u$, we find a rough limit on thedimensionless coupling constant for a neutrino-flavor independent coupling of$G<10^{-10}$, to avoid the effective number of light neutrinos in the earlyuniverse being essentially six. If, on the other hand, we wish to fine-tune themodel to give a more modest excess over three in the effective neutrinonumber, as may be needed according to recent WMAP analyses, it is easy to doso.\pacs{13.15.+g}



Author: R. F. Sawyer

Source: https://arxiv.org/







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