Asymptotic methods in stochastic control and applications in finance

Abstract : In this thesis, we study several mathematical finance problems related to the presence of market imperfections. Our main approach for solving them is to establish a relevant asymptotic framework in which explicit approximate solutions can be obtained for the associated control problems. In the first part of this thesis, we are interested in the pricing and hedging of European options. We first consider the question of determining the optimal rebalancing dates for a replicating portfolio in the presence of a drift in the underlying dynamics. We show that in this situation, it is possible to generate positive returns while hedging the option and describe a rebalancing strategy which is asymptotically optimal for a mean-variance type criterion. Then we propose an asymptotic framework for options risk management under proportional transaction costs. Inspired by Leland’s approach, we develop an alternative way to build hedging portfolios enabling us to minimize hedging errors. The second part of this manuscript is devoted to the issue of tracking a stochastic target. The agent aims at staying close to the target while minimizing tracking efforts. In a small costs asymptotics, we establish a lower bound for the value function associated to this optimization problem. This bound is interpreted in term of ergodic control of Brownian motion. We also provide numerous examples for which the lower bound is explicit and attained by a strategy that we describe. In the last part of this thesis, we focus on the problem of consumption-investment with capital gains taxes. We first obtain an asymptotic expansion for the associated value function that we interpret in a probabilistic way. Then, in the case of a market with regime-switching and for an investor with recursive utility of Epstein-Zin type, we solve the problem explicitly by providing a closed-form consumption-investment strategy. Finally, we study the joint impact of transaction costs and capital gains taxes. We provide a system of corrector equations which enables us to unify the results in [Homogenization and asymptotics for small transaction costs, M.Soner and N. Touzi, 2013] and [Asymptotics for Merton problem with small capital gain tax and interest rate, X. Chen and M. Dai, 2013].
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  • HAL Id : tel-01297282, version 1

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Jiatu Cai. Asymptotic methods in stochastic control and applications in finance. Computational Finance [q-fin.CP]. Université Paris Diderot, 2016. English. ⟨tel-01297282⟩

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