Itô versus Stratonovich in a stochastic cosmological model

Abstract: In this work we study a stochastic version of the Friedmann acceleration equation. This model has been proposed in the cosmology literature as a possible explanation of the uncertainty found in the experimental quantification of the Hubble parameter. Its noise has been tacitly interpreted in the Stratonovich sense. Herein we prove that this interpretation leads to a positive probability of finite time blow-up of the solution, that is, of the Hubble parameter. In contrast, if we just modify the noise interpretation to that of It^o, then the solution globally exists almost surely. Moreover, the expected asymptotic behavior is found under this interpretation too.