Hawking-like radiation in a FRW universe

In this article we study Hawking-like radiation from a Friedmann-Robertson- Walker (FRW) universe using the quasi-classical WKB/tunneling method. In calculating the correct temperature of the Hawking-like radiation we emphasize two important points: (i) the canonical invariance of the tunneling amplitude and (ii) existence of a temporal contribution to the tunneling amplitude. We also study back reaction and energy conservation of the radiated particles and find that the tunneling probability and change in entropy are related by Γ∝exp[-Δ∑] which differs from the standard result of Γ∝exp[+Δ∑]. This discrepancy if accounted for by regarding the whole FRW universe as an isolated adiabatic system whose change in total entropy is zero i.e. Δ∑total=Δ∑ int+Δ∑ext=0. © 2010 American Institute of Physics.