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While absence of arbitrage in frictionless financial markets requires price processes to be semimartingales, non-semimartingales can be used to model prices in an arbitrage-free way, if proportional transaction costs are taken into account. In this paper, we show, for a class of price processes which are not necessarily semimartingales, the existence of an… (More)

- Christoph Czichowsky
- Finance and Stochastics
- 2013

For portfolio optimisation under proportional transaction costs, we provide a duality theory for general càdlàg price processes. In this setting, we prove the existence of a dual optimiser as well as a shadow price process in a generalised sense. This shadow price is defined via a “sandwiched” process consisting of a predictable and an optional strong… (More)

- Christoph Czichowsky, Freddy Delbaen, +6 authors Johannes Wissel
- 2010

In this thesis we study the utility maximization problem for power utility random elds in a general semimartingale nancial market, with and without intermediate consumption. The notion of an opportunity process is introduced as a reduced form of the value process for the resulting stochastic control problem. This process is shown to describe the key… (More)

- Christoph Czichowsky, Johannes Muhle-Karbe, Walter Schachermayer
- SIAM J. Financial Math.
- 2014

In a financial market with a continuous price process and proportional transaction costs we investigate the problem of utility maximization of terminal wealth. We give sufficient conditions for the existence of a shadow price process, i.e. a least favorable frictionless market leading to the same optimal strategy and utility as in the original market under… (More)

Given a sequence (M)n=1 of non-negative martingales starting at M n 0 = 1 we find a sequence of convex combinations (M̃)n=1 and a limiting process X such that (M̃n τ ) ∞ n=1 converges in probability to Xτ , for all finite stopping times τ . The limiting process X then is an optional strong supermartingale. A counter-example reveals that the convergence in… (More)

The present paper accomplishes a major step towards a reconciliation of two conflicting approaches in mathematical finance: on the one hand, the mainstream approach based on the notion of no arbitrage (Black, Merton & Scholes); and on the other hand, the consideration of non-semimartingale price processes, the archetype of which being fractional Brownian… (More)

- Francesca Biagini, Rene Carmona, +31 authors Christoph Czichowsky
- 2015

For portfolio choice problems with proportional transaction costs, we discuss whether or not there exists a shadow price, i.e., a least favorable frictionless market extension leading to the same optimal strategy and utility. By means of an explicit counter-example, we show that shadow prices may fail to exist even in seemingly perfectly benign situations,… (More)

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