Title: A Downside Risk Analysis based on Financial Index Tracking Models Authors: Lian Yu and Xun Yu Zhou and Shuzhong Zhang Department of Systems Engineering and Engineering Management The Chinese University of Hong Kong Shatin, Hong Kong Abstract: This paper is mainly concerned with a single-stage financial index tracking problem under the downside risk constraint where short-selling is allowed. First, we formulate the portfolio selection model with the downside probability constraint to track the financial index. Due to the convexity of this problem, the optimal portfolio is derived analytically by applying the Karush-Kuhn-Tucker optimality conditions. Moreover, we extend the risk measure to higher order moment of the downside and study the corresponding portfolio optimization problem.