  Starting from the Poincare Gauge principle and a Starobinsky-Yang-Mills type
Lagrangian a model of dark energy is developed. In order to evade any
unnecessary controversy regarding frames (i.e. Einstein .vs. Jordan) the theory
is treated using the original variables instead of transforming them to a
scalar-tensor theory. The field equations are derived directly from the
original Lagrangian using the variational principle. The cosmological equations
are different from the Friedmann equations, but the acceleration equation gives
the same result as the one of the $\Lambda $CDM model in the matter-dominated
era. Furthermore, it indicates an inflation in the early time and the
radiation-dominated era as the Starobinsky model. The cosmological constant
naturally emerges from the Yang-Mills terms of the Lagrangian rather than be
added artificially. The equation of state of the dark energy depends on the
density of the matter and then the coincidence and fine tuning problem is
solved naturally.
  In order to compare with the popular $\Lambda $CDM model, the cosmological
perturbations is investigated. The equations for linear perturbations of the
metric and for the density contrast growth are derived. The explicit analytic
solutions are obtained. The gravitational potential and the growth of the
baryon matter density perturbation can be used to clarify whether this model is
in agreement with standard $\Lambda $CDM predictions and experimental data.
