  We derive the quantum energy-momentum tensor and the corresponding quantum
equation of state for gauge field theory using the effective Lagrangian
approach. The energy-momentum tensor has a term proportional to the space-time
metric and provides a finite non-diverging contribution to the effective
cosmological term. This allows to investigate the influence of the gauge field
theory vacuum polarisation on the evolution of Friedmann cosmology, inflation
and primordial gravitational waves. The Type I-IV solutions of the Friedmann
equations induced by the gauge field theory vacuum polarisation provide an
alternative inflationary mechanism and a possibility for late-time
acceleration. The Type II solution of the Friedmann equations generates the
initial exponential expansion of the universe of finite duration and the Type
IV solution demonstrates late-time acceleration. The solutions fulfil the
necessary conditions for the amplification of primordial gravitational waves.
