Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2007-10-26
Eur.Phys.J.C60:317-321,2009
Physics
High Energy Physics
High Energy Physics - Phenomenology
5 pages; v3, journal version;
Scientific paper
10.1140/epjc/s10052-009-0888-3
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. We calculate $T_D$ and $\rho_\U(T^0_\gamma)$ using photon-unparticle interactions for illustration.
Chen Shao-Long
He Xiao-Gang
Hu Xue-Peng
Liao Yanbiao
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