Motivated by recent results from the Super-Kamiokande experiment which indicate that neutrinos may have finite masses and provide at least part of the dark matter in the Universe, we have re-examined the decaying neutrino hypothesis of Sciama, including for the first time the effects of absorption by intergalactic dust. Earlier constraints have been weakened, especially in the case of very small dust grains (for which there is independent evidence). However, this is not enough to alter the conclusion that the model is only marginally consistent with observational data. The strongest constraints come from a new analysis of Voyager data by Murthy et al. (1999), which appear to rule out the theory, but ideally should be confirmed by further experiments. At best, Sciama's theory suggests that dust grains may be considerably smaller than has so far been assumed in most studies, and that their collective density is at the upper end of the range suggested by reddening and obscuration of quasars. At worst, the theory with more conventional dust data is incompatible with observation.
© European Southern Observatory (ESO) 1999
Online publication: August 25, 1999