Probing the Big Bang with quantum fields

By carrying out a systematic investigation of linear, test quantum fields ˆϕ(x) in cosmological space-times, we show that ˆϕ(x) remain well-defined across the big bang as operator valued distributions in a large class of Friedmann, Lemaˆıtre, Robertson, Walker space-times, including radiation and dust filled universes. In particular, the expectation values ⟨ˆϕ(x) ˆϕ(x′)⟩ are well-defined bidistributions in the extended space-time in spite of the big bang singularity. Interestingly, correlations between fields evaluated at spatially and temporally separated points exhibit an asymmetry that is reminiscent of the Belinskii, Khalatnikov, Lifshitz behavior. The renormalized products of fields ⟨ˆϕ2(x)⟩ren and ⟨ ˆ Tab(x)⟩ren also remain well-defined as distributions. Conformal coupling is not necessary for these considerations to hold.