We use scalar-field Lagrangians with a non-canonical kinetic term to obtain
unified dark matter models where both the dark matter and the dark energy, the
latter mimicking a cosmological constant, are described by the scalar field
itself. In this framework, we propose a technique to reconstruct models where
the effective speed of sound is small enough that the scalar field can cluster.
These models avoid the strong time evolution of the gravitational potential and
the large Integrated Sachs-Wolfe effect which have been a serious drawback of
previously considered models. Moreover, these unified dark matter scalar field
models can be easily generalized to behave as dark matter plus a dark energy
component behaving like any type of quintessence fluid.Comment: 26 pages, 1 figur
