arXiv:1304.2821hep-ph
How stable is the photon?
Early discovery. Linked by one identifiable commenter. This paper is outside the main ranking; a mention is not an endorsement.
Abstract
Yes, the photon. While a nonzero photon mass has been under experimental and theoretical study for years, the possible implication of a finite photon lifetime lacks discussion. The tight experimental upper bound of the photon mass restricts the kinematically allowed final states of photon decay to the lightest neutrino and/or particles beyond the Standard Model. We discuss the modifications of the well-measured cosmic microwave background spectrum of free streaming photons due to photon mass and lifetime and obtain model-independent constraints on both parameters---most importantly a lower direct bound of 3 yr on the photon lifetime, should the photon mass be at its conservative upper limit. In that case, the lifetime of microwave photons will be time-dilated by a factor order 10^(15).
The 3 years/10^18 figures I used were taken from https://arxiv.org/pdf/1304.2821.pdf : "Using the largest allowed value for the photon mass from other experiments, we find a lower limit of about 3 yr on the photon rest-frame lifetime. For photons in the visible spectrum, this…
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