A new recipe for $$\Lambda $$ Λ CDM

• Main Authors: Varun Sahni, Anjan A. Sen
• Format: Article
• Language: English
• Published: SpringerOpen 2017-04-01
• Series: European Physical Journal C: Particles and Fields
• Subjects: Dark Matter; Dark Energy; Scalar Field; Sterile Neutrino; Cold Dark Matter
• Online Access: http://link.springer.com/article/10.1140/epjc/s10052-017-4796-7
• ISSN: 1434-6044; 1434-6052

Abstract 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 $${\mathcal {L}} \propto X^\alpha - V(\phi )$$ L ∝ X α - V ( ϕ ) where $$\alpha \ge 1$$ α ≥ 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, $$\alpha \gg 1$$ α ≫ 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 $$\alpha $$ α . For very large values of $$\alpha $$ α the clustering properties of our model resemble those of cold dark matter (CDM). But for smaller values of $$\alpha $$ α , 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 $$\Lambda $$ Λ CDM, while its clustering properties are akin to those of either cold or warm dark matter.