  A mechanism to control the cosmological constant through a scalar field
non-minimally coupled to gravity is proposed. By utilizing non-minimal phantom
or quintessence, the cosmological constant, which may be large originally, can
be automatically driven to a value on the scale of the mass parameter in the
phantom/quintessence potential V(phi). The reduction of a large cosmological
constant involves the weakening of gravity that therefore may be much stronger
initially. There exist the cases where originally gravity is on the TeV scale
so that the hierarchy between gravity and three gauge interactions in the
standard model of particle physics is bridged at the beginning. Although the
cosmological constant can be automatically tuned or largely reduced under this
mechanism, its energy density may still remain on the same order of magnitude
as the original one. Thus, explaining the smallness of the
observation-suggested cosmological constant energy density is still a difficult
mission yet to be completed.
