A new recipe for

It is well known that a canonical scalar field is able to describe either dark matter or dark energy but not both. We demonstrate that a non-canonical scalar field can describe both dark matter and dark energy within a unified setting. We consider the simplest extension of the canonical Lagrangian $${\mathcal {L}} \propto X^\alpha - V(\phi )$$ where $$\alpha \ge 1$$ and V is a sufficiently flat potential. In this case the kinetic term in the Lagrangian behaves just like a perfect fluid, whereas the potential term mimicks dark energy. For very large values, $$\alpha \gg 1$$, the equation of state of the kinetic term drops to zero and the universe expands as if filled with a mixture of dark matter and dark energy. The velocity of sound in this model and the associated gravitational clustering are sensitive to the value of $$\alpha $$. For very large values of $$\alpha $$ the clustering properties of our model resemble those of cold dark matter (CDM). But for smaller values of $$\alpha $$, gravitational clustering on small scales is suppressed, and our model has properties resembling those of warm dark matter (WDM). Therefore our non-canonical model has an interesting new property: its expansion history resembles $$\Lambda $$CDM, while its clustering properties are akin to those of either cold or warm dark matter