Decoherence problem in an ekpyrotic phase

Quantum decoherence and the transition to semiclassical behavior during inflation have been extensively considered in the literature. In this paper, we use a simple model to analyze the same process in ekpyrosis. Our result is that the quantum to classical transition would not happen during an ekpyrotic phase even for superhorizon modes, and therefore the fluctuations cannot be interpreted as classical. This implies the prediction of a scale-free power spectrum in an ekpyrotic/cyclic universe model requires more inspection. DOI: 10.1103/PhysRevD.87.023518