Analysis and numerical solution of an inverse first passage problem from risk management

We study the following "inverse first passage time" problem. Given a diffusion process Xt and aprobability distribution q(t) on t &ge 0, does there exist a boundary b(t) such that q(t)=P[&tau &ge t], where &tau is the first hitting time of Xt to the time dependent level b(t). We formulate the inverse first passage time probleminto a free boundary problem for a parabolic partial differential operator and prove there exists a unique viscosity solution to the associated Partial Differential Equation by using the classical penalization technique. In order to compute the free boundary with a given default probability distribution, we investigate the small time behavior of the boundary b(t), presenting both upper and lower bounds first. Then we derive some integral equations characterizing the boundary. Finally we apply Newton-iteration on one of them to compute the boundary. Also we compare our numerical scheme with some other existing ones

One-dimensional reflected diffusions with two boundaries and an inverse first-hitting problem

We study an inverse first-hitting problem for a one-dimensional, time-homogeneous diffusion $X(t)$ reflected between two boundaries $a$ and $b,$ which starts from a random position $\eta.$ Let $a \le S \le b$ be a given threshold, such that $P( \eta \in [a,S])=1,$ and $F$ an assigned distribution function. The problem consists of finding the distribution of $\eta$ such that the first-hitting time of $X$ to $S$ has distribution $F.$ This is a generalization of the analogous problem for ordinary diffusions, i.e. without reflecting, previously considered by the author

The arctangent law for a certain random time related to a one-dimensional diffusion

For a time-homogeneous, one-dimensional diffusion process $X(t),$ we investigate the distribution of the first instant, after a given time $r,$ at which $X(t)$ exceeds its maximum on the interval $[0,r],$ generalizing a result of Papanicolaou, which is valid for Brownian motion

On the excursions of drifted Brownian motion and the successive passage times of Brownian motion

By using the law of the excursions of Brownian motion with drift, we find the distribution of the $n-$th passage time of Brownian motion through a straight line $S(t)= a + bt.$ In the special case when $b = 0,$ we extend the result to a space-time transformation of Brownian motion.Comment: 4 figures, accepted for publication in Physica