Induced moduli oscillation by radiation and space expansion in a higher-dimensional model

We investigate the cosmological expansion of the 3D space in a 6D model compactified on a sphere, beyond the 4D effective theory analysis. We focus on a case where the initial temperature is higher than the compactification scale. In such a case, the pressure for the compact space affects the moduli dynamics and induces the moduli oscillation even if they are stabilized at the initial time. Under some plausible assumptions, we derive the explicit expressions for the 3D scale factor and the moduli background in terms of analytic functions. Using them, we evaluate the transition times between different cosmological eras as functions of the model parameters and the initial temperature.