Quantum quench in interacting field theory: A self-consistent approximation

We study a composite quantum quench of the energy gap and the interactions in the interacting φ⁴ model using a self-consistent approximation. First we review results for free theories where a quantum quench of the energy gap or mass leads for long times to stationary behavior with thermal characteristics. An exception to this rule is the $2d$ case with zero mass after the quench. In the composite quench, however, we find that the effect of the interactions in our approximation is simply to effectively change the value of the mass. This means on the one hand that the interacting model also exhibits the same stationary behavior and on the other hand that this is now true even for the massless $2d$ case.