Fundamental constants and cosmic vacuum: the micro and macro connection
  The idea that the vacuum energy density $\rho_{\Lambda}$ could be time
dependent is a most reasonable one in the expanding Universe; in fact, much
more reasonable than just a rigid cosmological constant for the entire cosmic
history. Being $\rho_{\Lambda}=\rho_{\Lambda}(t)$ dynamical, it offers a
possibility to tackle the cosmological constant problem in its various facets.
Furthermore, for a long time (most prominently since Dirac's first proposal on
a time variable gravitational coupling) the possibility that the fundamental
"constants" of Nature are slowly drifting with the cosmic expansion has been
continuously investigated. In the last two decades, and specially in recent
times, mounting experimental evidence attests that this could be the case. In
this paper, we consider the possibility that these two groups of facts might be
intimately connected, namely that the observed acceleration of the Universe and
the possible time variation of the fundamental constants are two manifestations
of the same underlying dynamics. We call it: the "micro and macro connection",
and on its basis we expect that the cosmological term in Einstein's equations,
Newton's coupling and the masses of all the particles in the Universe, both the
dark matter particles and the ordinary baryons and leptons, should all drift
with the cosmic expansion. Here we discuss specific cosmological models
realizing such possibility in a way that preserves the principle of covariance
of General Relativity.
