We propose a simplified approach to mean-variance portfolio problems by changingtheir parametrisation from trading strategies to final positions. This allows us to treat,under a very mild no-arbitrage-type assumption, a whole range of quadratic optimisationproblems by simple mathematical tools...

The Markowitz problem consists of finding in a financial market a self-financingtrading strategy whose final wealth has maximal mean and minimal variance. Westudy this in continuous time in a general semimartingale model and under coneconstraints: Trading strategies must take values in a...

An equivalent !-martingale measure (E!MM) for a given stochastic process Sis a probability measure R equivalent to the original measure P such that S isan R-!-martingale. Existence of an E!MM is equivalent to a classical absenceof-arbitrage property of S, and is invariant if we replace the...

We solve the problem of mean-variance hedging for general semimartingale modelsvia stochastic control methods. After proving that the value process of theassociated stochastic control problem has a quadratic structure, we characteriseits three coefficient processes as solutions of semimartingale...

We study mean-variance hedging under portfolio constraints in a general semi-martingale model. The constraints are formulated via predictable correspondences,meaning that the trading strategy is restricted to lie in a closed convex set whichmay depend on the state and time in a predictable way....

We study a quadratic BSDE in a continuous filtration with an unbounded generatorand an infinite time horizon. This equation comes from a stochasticcontrol problem in the context of robust utility maximisation.[...]

We consider backward stochastic dierential equations (BSDEs) witha particular quadratic generator and study the behaviour of their solu-tions when the probability measure is changed, the ltration is shrunk,or the underlying probability space is transformed.[...]

Let S be an Rd-valued semimartingale and ( n) a sequence of C-valued inte-grands, i.e., predictable, S-integrable processes taking values in some given closedset C(!, t) ⊆ Rd which may depend on the state ! and time t in a predictable way.Suppose that the stochastic integrals ( n · S)...

We study the exponential utility indifference valuation of a contingentclaim H when asset prices are given by a general semimartingale S. Under mildassumptions on H and S, we prove that a no-arbitrage type condition is fulfilled ifand only if H has a certain representation. In this case, the...