  We investigate a cosmological model in which dark energy identified with the
vacuum energy which is running and decaying. In this model vacuum is metastable
and decays into a bare (true) vacuum. This decaying process has a quantum
nature and is described by tools of the quantum decay theory of unstable
systems. We have found formulas for an asymptotic behavior of the energy
density of dark energy in the form of a series of inverse powers of the
cosmological time. We investigate the dynamics of FRW models using dynamical
system methods as well as searching for exact solutions. From dynamical
analysis we obtain different evolutional scenarios admissible for all initial
conditions. For the interpretation of the dynamical evolution caused by the
decay of the quantum vacuum we study the thermodynamics of the apparent horizon
of the model as well as the evolution of the temperature. For the early
Universe, we found that the quantum effects modified the evolution of the
temperature of the Universe. In our model the adiabatic approximation is valid
and the quantum vacuum decay occurs with an adequate unknown particle which
constitutes quantum vacuum. We argue that the late-time evolution of metastable
energy is the holographic dark energy.
