Variation in the fine-structure constant and the distance-duality relation

The possibility of variation of the fundamental constants of nature has been a long-standing question, with important consequences for fundamental physics and cosmology. In particular, it has been shown that variations in the fine-structure constant, alpha, are directly related to violation of the distance duality relation (DDR), which holds true as long as photons travel on unique null geodesics and their number is conserved. In this paper we use the currently available measurements of Delta alpha/alpha to impose the most stringent constraints on departures of the DDR to date, here quantified by the parameter eta(0). From the observational data we obtain constraints on eta(0) of the order of 10(-7), the most stringent constraints on a possible violation of the DDR to date.