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A tight constraint on some varying speed of light theories

Ahmad Shariati·Nosratollah Jafari
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Abstract

We argue that if the velocity of electromagnetic waves in vacuum, \cem, is different from the limiting velocity for massive particles, \cst, then, a proton moving with velocity $\cem < v < \cst$ would radiate Cherenkov radiation. Because we have seen protons with energy $\sim 10^{19}$ eV coming from a distance of order more than 1 Mpc, we can put a constraint on $Δ:= (\cst - \cem)/\cst$: $Δ< 10^{-27}$.

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Ahmad Shariati, Nosratollah Jafari. 2005-02-15. A tight constraint on some varying speed of light theories. https://arxiv.org/abs/gr-qc/0502071

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