OPTIMAL PORTFOLIO SELECTION STRATEGIES IN THE PRESENCE OF TRANSACTION COSTS

We consider an investor who has available a bank account (risk free asset) and a stock (risky asset). It is assumed that the interest rate for the risk free asset is zero and the stock price is modeled by a diffusion process. The wealth can be transferred between the two assets under a proportional transaction cost. Investor is allowed to obtain loans from the bank and also to short-sell the risky asset when necessary. The optimization problem addressed here is to maximize the probability of reaching a financial goal a before bankruptcy and to obtain an optimal portfolio selection policy. Our optimal policy is a combination of local-time processes and jumps. In the interesting case, it is determined by a non-linear switching curve on the state space. This work is a generalization of Weerasinghe [20], where this switching boundary is a vertical line segment.