Miklós Rásonyi — Page 3

arXiv2009

Hiding a drift

In this article we consider a Brownian motion with drift of the form \[dS_t=μ_t dt+dB_t\qquadfor t\ge0,\] with a specific nontrivial $(μ_t)_{t\geq0}$, predictable with respect to $\mathbb{F}^B$, the natural filtration of the Brownian motion $B=(B_t)_{t\ge0}$. We construct a process $H=(H_t)_{t\ge0}$, also predictable with respect to $\mathbb{F}^B$, such that $((H\cdot S)_t)_{t\ge 0}$ is a Brownian motion in its own filtration. Furthermore, for any $δ>0$, we refine this construction such that the drift $(μ_t)_{t\ge0}$ only takes values in $]μ-δ,μ+δ[$, for fixed $μ>0$.

math.PR↗

arXiv2008

Consistent price systems and face-lifting pricing under transaction costs

In markets with transaction costs, consistent price systems play the same role as martingale measures in frictionless markets. We prove that if a continuous price process has conditional full support, then it admits consistent price systems for arbitrarily small transaction costs. This result applies to a large class of Markovian and non-Markovian models, including geometric fractional Brownian motion. Using the constructed price systems, we show, under very general assumptions, the following ``face-lifting'' result: the asymptotic superreplication price of a European contingent claim $g(S_T)$ equals $\hat{g}(S_0)$, where $\hat{g}$ is the concave envelope of $g$ and $S_t$ is the price of the asset at time $t$. This theorem generalizes similar results obtained for diffusion processes to processes with conditional full support.

q-fin.PR↗