Announcing

1. Announcing 理論科学コロキウムのお知らせ From 3:30 pm, January 20th (Wed), 2010 At Room 435,437, Main Research Building Theoretical Science Colloquium Toshikazu EBISUZAKI Lecturer: from Computational Atrophysics Laboratory Gamma-ray Signal from Earth-mass Dark Matter Microhalos On *The lecture will be delivered in English. Summary:Earth-mass dark matter microhalos are the first structures formed in the universe, if we consider neutralino as the dark matter candidate. If these halos have survived to the present time, they would be the primary places for the dark-matter annihilation, whose signature might have already been observed as electron and positron excess. Early studies suggested that a noticeable fraction of microhalos born in early universe have survived up to present time and they might be observed as the dominant sources of the annihilation signal. On the other hand, others claimed that these microhalos cannot survive. Here, we report the results of ultra-high-resolution simulation (particle mass of ∼ 10−12 solar mass) of the formation and evolution of these microhalos. We found that microhalos have the central density cusp of the form ρ ∝ r−1.5, much steeper than the cusp of larger dark halos. The very central regions of these microhalos survive the encounters with stars down to the radius of a few kpcs from the galactic center. The nearest microhalos should be visible as point sources (radius less than 1’), with proper motion of ∼ 0.2 degree per year. Also, we might be able to use the millisecond pulsar timing measurements by PPTA to detect microhalos. 講師：　戎崎俊一氏 　（戎崎計算宇宙物理研究室） タイトル：Gamma-ray Signal From Earth-mass Dark Matter Microhalos 日時： 1月20日（水） 　　　　午後3時３０分より 場所：研究本館4階 435,437号室 The Theoretical Science Colloquium is an effort towards integrating researchers who study theoretical science in RIKEN. http://www.riken.jp/lab-www/theory/colloquium/