Decoherence of Primordial Fluctuations During Inflation: When Quantum-to-Classical Transition Completes

This paper estimates, in a transparent proxy model, how quickly primordial fluctuations decohere during inflation as a function of their coupling to an environment sector. For a coupling of one hundredth, decoherence completes in about 2.30 e-folds in the proxy; for a coupling of one ten-thousandth it takes about 4.61 e-folds. The inflationary expansion rate adopted corresponds to 1.519e+37 per second. Even weak couplings decohere the fluctuations well before the end of a sixty-e-fold inflationary phase in this model, supporting the standard practice of treating the fluctuations classically at horizon exit while leaving the precise mechanism model-dependent. A density ceiling, if it caps the inflationary density, would lower the expansion rate and lengthen these times modestly; it does not change the ordering. The study is simulated and computed from stated assumptions; it is not a measurement.