A Friedmann-Lemaitre-Robertson-Walker cosmological model with running Lambda

The idea of a variable dark energy has been entertained many times in the literature and from many different points of view. Quintessence is just a popular way to implement this idea in recent times, but so far with little success. Another possibility is to think of the cosmological term, Lambda, as a running quantity'' much in the same way as the electromagnetic coupling constant. However, the fact that Lambda is a dimension-four parameter implies that it may obey a peculiar renormalization group equation, which at low energies could be dominated by soft decoupling’’ contributions of the form Lambda ~ H^2 M_P^2 stemming from physics near the Planck scale. This value lies in the ballpark of the measurements from CMB and high-z supernovae. A ``renormalized’’ FLRW cosmology of this kind may reveal itself as a sound, and testable, proposal for a variable Lambda model within quantum field theory in curved space time.