Direct photon production in $e^{+}$$e^{\mathrm{-}}$ collisions

We study the process $e^{+}$$e^{\mathrm{-}}$→γ+X as a possible test to distinguish between fractionally-charged-quark models and gauged integer-charged-quark models. We find that charge-asymmetry measurement in this process would not distinguish between the two models, contrary to earlier statements in the literature. However, we show that a direct measurement of this process would serve to clearly distinguish the two models, if the relevant energies are above color threshold. We find that the integer-charged-quark-model cross sections are enhanced by a factor of 1.7–1.8 above the values given by the fractionally-charged-quark model, in the kinematic ranges where a clean signal is expected. We also show that this process cannot clearly distinguish between the two models if the relevant energies are below color threshold.