Abstract
To model a realistic situation for the beginning we consider massive real scalar $\phi^4$ theory in a (1+1)-dimensional asymptotically static Minkowski spacetime with an intermediate stage of expansion. To have an analytic headway we assume that scalars have a big mass. At past and future infinities of the background we have flat Minkowski regions which are joint by the inflationary expansion region. We use the tree-level Keldysh propagator in the theory in question to calculate the expectation value of the stress-energy tensor which is, thus, due to the excitations of the zero-point fluctuations. Then we show that even for large mass, if the de Sitter expansion stage is long enough, the quantum loop corrections to the expectation value of the stress-energy tensor are not negligible in comparison with the tree-level contribution. That is revealed itself via the excitation of the higher-point fluctuations of the exact modes: During the expansion stage a non-zero particle number density for the exact modes is generated. This density is not Plankian and serves as a quench which leads to a thermalization in the out Minkowski stage.
Highlights
Standard reheating [1] after inflation [2,3,4,5], demands the presence of an inflaton field
That is revealed itself via the excitation of the higher-point fluctuations of the exact modes: during the expansion stage a nonzero particle number density for the exact modes is generated
The so-called one-loop expectation value of the stress-energy tensor, which is calculated with the use of the tree-level two-point Hadamard function or Keldysh propagator usually does not provide strong contributions to the particle number density after inflation
Summary
Standard reheating [1] after inflation [2,3,4,5], demands the presence of an inflaton field. The other secular effects are present in generic nonstationary situations and appear when the time separation between arguments of the two-point function is growing (see e.g. introduction of [56] for the review). It goes without saying that for light fields there can be even more dramatic effects [56] It is known in condensed matter theory that in nonstationary situations generally loop corrections can be strong [58,59] for various reasons. The secular effect of interest for us in the present paper is due to the excitation of the higher levels (on top of the zeropoint fluctuations) of the exact modes in the background gravitational field This is due to the nonstationarity of the inflationary expansion and due to the presence of interactions in the quantum field theory [57] (see [56]).
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