科研之友
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摘要
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 L proportional to X-alpha - V(phi) where alpha >= 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 >> 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 orwarm darkmatter.
- 出版日期2017-4-10
