Particle physics must be taken into account in cosmological models of the early universe, when the average energy density was very high.
This means that particle physics processes involving pion decay can be neglected until roughly that much time has passed since the Big Bang.
Cosmological observations of phenomena such as the cosmic microwave background and the cosmic abundance of elements, together with the predictions of the Standard Model of particle physics, place constraints on the physical conditions in the early universe.
The success of the Standard Model at explaining these observations support its validity under conditions beyond those which can be produced in a laboratory.
Conversely, phenomena discovered through cosmological observations, such as dark matter and baryon asymmetry, suggest the presence of physics that goes beyond the Standard Model.