Quantum corrections to the Classical Statistical Approximation for the expanding quantum field

Understand

We found the deviation of the equation of state from ultrarelativistic one due to quantum corrections for a nonequilibrium longitudinally expanding scalar field.

• Relaxation of highly excited quantum field is usually described in terms of Classical Statistical Approximation (CSA).
• However, the expansion of the system reduces the applicability of such a semiclassical approach as the CSA making quantum corrections important.
• We calculate the evolution of the trace of the energy-momentum tensor within the Keldysh-Schwinger framework for static and longitudinal expanding geometries.