, Volume 145, Issue 3-4, pp 285-335
Date: 28 May 2009

Time-Dependent Nuclear Decay Parameters: New Evidence for New Forces?

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This paper presents an overview of recent research dealing with the question of whether nuclear decay rates (or half-lives) are time-independent constants of nature, as opposed to being parameters which can be altered by an external perturbation. If the latter is the case, this may imply the existence of some new interaction(s) which would be responsible for any observed time variation. Interest in this question has been renewed recently by evidence for a correlation between nuclear decay rates and Earth–Sun distance, and by the observation of a dip in the decay rate for 54Mn coincident in time with the solar flare of 2006 December 13. We discuss these observations in detail, along with other hints in the literature for time-varying decay parameters, in the framework of a general phenomenology that we develop. One consequence of this phenomenology is that it is possible for different experimental groups to infer discrepant (yet technically correct) results for a half-life depending on where and how their data were taken and analyzed. A considerable amount of attention is devoted to possible mechanisms which might give rise to the reported effects, including fluctuations in the flux of solar neutrinos, and possible variations in the magnitudes of fundamental parameters, such as the fine structure constant and the electron-to-proton mass ratio. We also discuss ongoing and future experiments, along with some implications of our work for cancer treatments, 14C dating, and for the possibility of detecting the relic neutrino background.