Fine structure constant variation from a late phase transition

Recent experimental data indicates that the fine structure constant α may be varying on cosmological time scales. We consider the possibility that such a variation could be induced by a second order phase transition which occurs at late times (z∼1–3) and involves a change in the vacuum expectation value (vev) of a scalar with milli-eV mass. Such light scalars are natural in supersymmetric theories with low SUSY breaking scale. If the vev of this scalar contributes to masses of electrically charged fields, the low-energy value of α changes during the phase transition. The observational predictions of this scenario include isotope-dependent deviations from Newtonian gravity at sub-millimeter distances, and (if the phase transition is a sharp event on cosmological time scales) the presence of a well-defined step-like feature in the α(z) plot. The relation between the fractional changes in α and the QCD confinement scale is highly model dependent, and even in grand unified theories the change in α does not need to be accompanied by a large shift in nucleon masses.