Cosmological constraints on unparticle dark matter

TL;DR

This paper uses cosmological observations to constrain unparticle dark matter models, finding that such unmatter cannot dominate the dark matter component and must have a high scaling dimension to be consistent with data.

Contribution

It provides the first observational constraints on unparticle dark matter parameters using combined cosmological data sets.

Findings

Unmatter with high scaling dimension ($d_U > 60$) is consistent with observations.

Unmatter can only constitute a few percent of dark matter if $d_U<10$.

Constraints are significantly improved when combining SNIa, BAO, and CMB data.

Abstract

In unparticle dark matter (unmatter) models the equation of state of the unmatter is given by $p=\rho/(2d_U+1)$, where $d_U$ is the scaling factor. Unmatter with such equations of state would have a significant impact on the expansion history of the universe. Using type Ia supernovae (SNIa), the baryon acoustic oscillation (BAO) measurements and the shift parameter of the cosmic microwave background (CMB) to place constraints on such unmatter models we find that if only the SNIa data is used the constraints are weak. However, with the BAO and CMB shift parameter data added strong constraints can be obtained. For the $\Lambda$UDM model, in which unmatter is the sole dark matter, we find that $d_U > 60$ at 95% C.L. For comparison, in most unparticle physics models it is assumed $d_U<2$. For the $\Lambda$CUDM model, in which unmatter co-exists with cold dark matter, we found that the unmatter can at most make up a few percent of the total cosmic density if $d_U<10$, thus it can not be the major component of dark matter.