  We aim at the construction of dark energy models without exotic matter but
with a phantom-like equation of state (an effective phantom phase). The first
model we consider is decaying vacuum cosmology where the fluctuations of the
vacuum are taken into account. In this case, the phantom cosmology (with an
effective, observational $\omega$ being less than -1) emerges even for the case
of a real dark energy with a physical equation of state parameter $\omega$
larger than -1. The second proposal is a generalized holographic model, which
is produced by the presence of an infrared cutoff. It also leads to an
effective phantom phase, which is not a transient one as in the first model.
However, we show that quantum effects are able to prevent its evolution towards
a Big Rip singularity.

High Energy Physics - Theory;Astrophysics;General Relativity and Quantum Cosmology