  In this work we perform some studies related to dark energy. Firstly, we
propose a dynamical approach to explain the dark energy content of the
universe. We assume that a massless scalar field couples to the Hubble
parameter with some Planck-mass suppressed interactions. This scalar field
developes a Hubble parameter-dependent (thus time-dependent) vacum expectation
value, which renders a time-independent relative density for dark energy and
thus can explain the coincidence of the dark energy density of the universe.
Secondly, we assume the dark matter particle is meta-stable and decays very
lately into the dark energy scalar field. Such a conversion of matter to dark
energy can give an explanation for the starting time of the accelerating
expansion of the universe. Thirdly, we introduce multiple Affleck-Dine fields
to the landscape scenario of dark energy in order to have the required
baryon-asymmetry universe.
