Thermal Unparticles: A New Form of Energy Density in the Universe

Understand

Unparticle $\U$ with scaling dimension $d_\U$ has peculiar thermal properties due to its unique phase space structure.

• We find that the equation of state parameter $\omega_\U$, the ratio of pressure to energy density, is given by $1/(2d_\U +1)$ providing a new form of energy in our universe.
• In an expanding universe, the unparticle energy density $\rho_\U(T)$ evolves dramatically differently from that for photons.
• For $d_\U >1$, even if $\rho_\U(T_D)$ at a high decoupling temperature $T_D$ is very small, it is possible to have a large relic density $\rho_\U(T^0_\gamma)$ at present photon temperature $T^0_\gamma$, large enough to play the role of dark matter.