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Modak and Singleton [Phys. Rev. D 86, 123515 (2012), 10.1103/PhysRevD.86.123515] have presented Hawking-like radiation for cosmological inflation which has a natural "turn on" and a natural "turn off" mechanism. This Hawking-like radiation results in an effective negative pressure "fluid" which leads to a rapid period of expansion in the very early Universe. We discuss that the turn on mechanism cannot happen for the Friedmann-Robertson-Walker model in the early Universe because its horizon is an apparent horizon not an event horizon. Hence, we cannot apply geometric optic approximation which is a necessary condition for the tunneling method. It was shown that this model predicts a value for Ï/mpl4 which is bigger than the COBE normalization constraint in the cosmic microwave background at the horizon exit. The authors of the paper offer a Reply.
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