Conditioned martingales

A simple path transformation is described which connects one-dimensional Brownian motion with the radial part of three-dimensional Brownian motion. This provides simple proofs of various path decompositions for these processes described by David Williams.

Firstly, we compute the distribution function for the hitting time of a linear time-dependent boundary t ↦ a + bt, a ≥ 0, b ∈ ℝ, by a reflecting Brownian motion. The main tool hereby is Doob’s formula which gives the probability that Brownian motion started inside a wedge does not hit this wedge. Other key ingredients are the time inversion property of Brownian motion and the time reversal property of diffusion bridges. Secondly, this methodology can also be applied for the three-dimensional Bessel process. Thirdly, we consider Bessel bridges from 0 to 0 with dimension parameter δ > 0 and show that the probability that such a Bessel bridge crosses an affine boundary is equal to the probability that this Bessel bridge stays below some fixed value.

In this paper, we present a switching property for squared Bessel process. We prove that the starting point and the time parameter can be in a sense switched. As a consequence, we obtain new distributional dependencies among a squared Bessel process R, a Brownian motion with drift $$ {B}^{\left(\mu \right)},\mu \ge 0,\left({B}_t^{\left(\mu \right)}:= {B}_t+\mu t\kern0.5em \mathrm{for}\ \mathrm{a}\ \mathrm{Brownian}\ \mathrm{motion}\ B\right), $$ and an integral functional of geometric Brownian motion A(μ) connected by the Lamperti relation. Finally, we deduce a new explicit form of the joint distribution of the Lamperti triple $$ \left({R}_T,{A}_t^{\left(\mu \right)},\exp \left(2{B}_t^{\left(\mu \right)}\right)\right) $$ for fixed t > 0 andT > 0.

Asymmetric skew Bessel processes and their applications to finance

Consider A Closed E of the Real Line R and a (Measureble) Function Defined on R and Strictly Concave on Every Component of R/E. The Present Paper Deals with the Following Marticgale Problem: Find a Continuous Local Martingale (X,F), Given on a Family () of Probability Spaces With for every such that x is stopped at the debut of e, and the process is a local martingale up to We show that this martingale problem possesses a unique solution. This solution is a strong Markov continuous local martingale. Furthermore, it is a pure continuous local martingale and therefore satisfies the previsible representation property. Conversely, for every strong Markov continuous local martingale (X,F) we can find a closed subset E of R and a function f strictly concave on every component of R\E such that (X, F) is the unique solution of the above martingale problem. In the particular case that E and f(X) we recover the theorem of P. Levy on the martingale characterization of the Brownian motion.

Filtering of absorbing and reflecting Brownian motions

Covariance and independence, rotational symmetry, isonormal Gaussian process, independent increments, Brownian motion and bridge, scaling and inversion, Gaussian Markov processes, quadratic variation, path irregularity, strong Markov and reflection properties, Bessel processes, maximum process, arcsine and uniform laws, laws of the iterated logarithm, Wiener integral, spectral and moving-average representations, Ornstein–Uhlenbeck process, multiple Wiener–Ito integrals, chaos expansion of variables and processes.

We present a new test for the “continuous martingale hypothesis”. That is, a test for the hypothesis that observed data are from a process which is a continuous local martingale. The basis of the test is an embedded random walk at first passage times, obtained from the well-known representation of a continuous local martingale as a continuous time-change of Brownian motion. With a variety of simulated diffusion processes our new test shows higher power than existing tests using either the crossing tree or the quadratic variation, including the situation where non-negligible drift is present. The power of the test in the presence of jumps is also explored with a variety of simulated jump diffusion processes. The test is also applied to two sequences of high-frequency foreign exchange trade-by-trade data. In both cases the continuous martingale hypothesis is rejected at times less than hourly and we identify significant dependence in price movements at these small scales.

Bessel processes with constant negative drift have recently appeared as heavy-traffic limits in queueing theory. We derive a closed-form expression for the spectral representation of the transition density of the Bessel process of orderν> −1 with constant driftμ≠ 0. Whenν> -½ andμ< 0, the first term of the spectral expansion is the steady-state gamma density corresponding to the zero principal eigenvalueλ0= 0, followed by an infinite series of terms corresponding to the higher eigenvaluesλn,n= 1,2,…, as well as an integral over the continuous spectrum aboveμ2/2. When −1 <ν< -½ andμ< 0, there is only one eigenvalueλ0= 0 in addition to the continuous spectrum. As well as applications in queueing, Bessel processes with constant negative drift naturally lead to two new nonaffine analytically tractable specifications for short-term interest rates, credit spreads, and stochastic volatility in finance. The two processes serve as alternatives to the CIR process for modelling mean-reverting positive economic variables and have nonlinear infinitesimal drift and variance. On a historical note, the Sturm–Liouville equation associated with Bessel processes with constant negative drift is closely related to the celebrated Schrödinger equation with Coulomb potential used to describe the hydrogen atom in quantum mechanics. Another connection is with D. G. Kendall's pole-seeking Brownian motion.

The goal of this chapter is to give a concise account of the connection between Bessel processes and the integral of geometric Brownian motion. The latter appears in the pricing of Asian options. Bessel processes are defined and some of their properties are given. The known expressions for the probability density function of the integral of geometric Brownian motion are stated, and other related results are given, in particular the Geman and Yor (1993) Laplace transform for Asian option prices.

Recently, van Neerven, Weis and the author, constructed a theory for stochastic integration of UMD Banach space valued processes. Here the authors use a (cylindrical) Brownian motion as an integrator. In this note we show how one can extend these results to the case where the integrator is an arbitrary real-valued continuous local martingale. We give several characterizations of integrability and prove a version of the Itô isometry, the Burkholder–Davis–Gundy inequality, the Itô formula and the martingale representation theorem.

A necessary and sufficient condition is given for a Brownian excursion law in a Lipschitz domain to share the local path properties with an excursion law in a halfspace. This condition is satisfied for all boundary points of every C1't-domain, ct > 0. There exists a Cl-domain such that the condition is satisfied almost nowhere on the boundary. A probabilistic interpretation and applications to minimal thinness and boundary behavior of Green functions are given. 0. Introduction. We will show that the local path properties of Brownian excursions in Cl,--domains, a > 0, are the same as the local path properties of Brownian excursions in a half-space (Theorem 3.1). This need not be the case if the domain is of class C' (Proposition 3.1). The method of proof is based on the exit system theory of Maisonneuve [12]. We will study Brownian excursion laws, i.e., one of the ingredients of an exit system. We will give a necessary and sufficient condition for an excursion law in a Lipschitz domain to have the same local path properties as an excursion law in a half-space (Theorems 2.1 and 2.2). This last result can be applied to obtain new criteria for minimal thinness (Theorem 4.1) and existence of a nondegenerate normal derivative for the Green function (Theorem 4.2). Local path properties of 1-dimensional Brownian excursions have been known for some time. They are the same as the local path properties of the 3-dimensional Bessel process (see ?2.10 of Ito and McKean [11] or ?II.67 of Williams [21]). Dvoretsky and Erd6s [8] and Shiga and Watanabe [18] have given Kolmogorov-type tests for Bessel processes. Local path properties of excursions of multidimensional Brownian motion have been studied by Shimura [19] (excursions of 2-dimensional Brownian motion from a line) and Burdzy [1] (n-dimensional case, n > 2). Our theorem about minimal thinness generalizes results of Essen and Jackson [9] and Burdzy [3, 4]. A new criterion for the existence of the nondegenerate normal derivative for the Green function extends some results of Widman [20], Rippon [17] and Burdzy [4]. The present article mainly uses ideas from excursion theory (see Maisonneuve [12], Williams [21] and Burdzy [1]) and potential theory (see Doob [7]). Received by the editors July 26, 1985. 1980 Mathematics Subject Classification (1985 Revision). Primary 60G17, 60J50, 60J65; Secondary 31B25, 60J45.

We show how a description of Brownian exponential functionals as a renewal series gives access to the law of the hitting time of a square-root boundary by a Bessel process. This extends classical results by Breiman and Shepp, concerning Brownian motion, and recovers by different means, extensions for Bessel processes, obtained independently by Delong and Yor.

The limitations of traditional indifference-zone (IZ) ranking and selection procedures stem from their reliance on an IZ parameter, which is often unknown in practice and can lead to inefficiencies. Additionally, since exact evaluation of the probability of correct selection (PCS) is generally unattainable, these approaches commonly rely on a Bonferroni-Inequality-type lower bound to ensure the worst-case PCS, which introduces further conservativeness. To overcome these challenges, we propose fully sequential IZ-free procedures that eliminate the need for an IZ parameter and reduce the conservativeness associated with Bonferroni Inequality approaches. We demonstrate that, in the context of IZ-free procedures, the screening statistic corresponds to the Euclidean distance of a multi-dimensional standard Brownian motion, which behaves as a Bessel process. This connection simplifies the derivation of statistical guarantees for the proposed procedures and facilitates the analytical expressions for key parameters. Our procedures accommodate both known equal variances and unknown unequal variances, with statistical guarantees established in the known equal variance case. Numerical experiments confirm that the proposed procedures outperform existing methods in reducing PCS conservativeness and improving sample size efficiency. These advancements enhance the robustness and practicality of IZ-free procedures for diverse applications.

This paper uses Lie symmetry methods to analyze boundary crossing probabilities for a large class of diffusion processes. We show that if the Fokker–Planck–Kolmogorov equation has non-trivial Lie symmetry, then the boundary crossing identity exists and depends only on parameters of process and symmetry. For time-homogeneous diffusion processes we found the necessary and sufficient conditions of the symmetries’ existence. This paper shows that if a drift function satisfies one of a family of Riccati equations, then the problem has nontrivial Lie symmetries. For each case we present symmetries in explicit form. Based on obtained results, we derive two-parametric boundary crossing identities and prove its uniqueness. Further, we present boundary crossing identities between different process. We show, that if the problem has 6 or 4 group of symmetries then the first passage time density to any boundary can be explicitly represented in terms of the first passage time by a Brownian motion or a Bessel process. Many examples are presented to illustrate the method.