  We consider that the cosmological constant is associated with the vacuum
energy density of a particle physics model. In the path integral formalism of
euclidean quantum gravity and in the background of the Robertson Walker metric
we calculate only the contribution of the matter density to the fluctuating
metric. This produces an effective term in the action that acts as a correction
to the vacuum energy density of the matter. The method leads to the observed
cosmological constant without the need of any fine tuning in the gravity or
particle physics sectors.

General Physics;General Relativity and Quantum Cosmology