Gauge Field Theory Vacuum and Cosmological Inflation
  The deep interrelation between elementary particle physics and cosmology
manifests itself when one considers the contribution of quantum fluctuations of
vacuum fields to the dark energy and the effective cosmological constant. The
contribution of zero-point energy exceeds by many orders of magnitude the
observational cosmological upper bound on the energy density of the universe.
Therefore it seems natural to expect that vacuum fluctuations of the
fundamental fields would influence the cosmological evolution in any way. Our
aim in this review article is to describe a recent investigation of the
influence of the Yang-Mills vacuum polarisation and of the chromomagnetic
condensation on the evolution of Friedmann cosmology, on inflation and on
primordial gravitational waves. 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 constant. 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.
