The Effect of Extra Dimension on Dark Matter.pdfVIP

The Effect of Extra Dimension on Dark Matter a NOBUCHIKA OKADA Theory Division, KEK, Oho 1-1, Tsukuba, Ibaraki 305-0801, Japan E-mail: okadan@post.kek.jp OSAMU SETO Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan 300, Republic of China 4 0 E-mail: osamu@mail.nctu.edu.tw 0 2 p ABSTRACT e S We investigate the thermal relic density of a cold dark matter in the brane world 5 cosmology. Since the expansion law in a high energy regime is modified from the 1 one in the standard cosmology, if the dark matter decouples in such a high energy regime its relic number density is affected by this modified expansion law. We 1 derive analytic formulas for the number density of the dark matter. It is found v 0 that the resultant relic density is characterized by the “transition temperature” 7 at which the modified expansion law in the brane world cosmology is connecting 1 with the standard one, and can be considerably enhanced compared to that 9 in the standard cosmology, if the transition temperature is low enough. The 0 implication to the neutralino dark matter also is mentioned. 4 0 / 1. Introduction h p p- Recent various cosmological observations have established the ΛCDM cosmological e model with a great accuracy, where the energy density in the present universe consists h