Speaker
Description
We calculate the energy density and pressure of a scalar field after its decoup-
ling from a thermal bath in the spatially flat Friedman–Lemaître–Robertson–
Walker space-time, within the framework of quantum statistical mechanics.
By using the density operator determined by the condition of local thermo-
dynamic equilibrium, we calculate the mean value of the stress-energy tensor
of a real scalar field by subtracting the vacuum expectation value at the time
of the decoupling. If the expansion rate is
comparable or larger than mass or the decoupling temperature, both energy density and pressure get strong quantum corrections which substantially modify
their classical dependence on the scale factor a(t) and drive pressure to large negative values.
