Sojourn times for Brownian sheet

Sojourn time in $\mathbb{Z}^+$ for the Bernoulli random walk on $\mathbb{Z}$

Let $(S_k)_{k\ge 1}$ be the classical Bernoulli random walk on the integer line with jump parameters $p\in(0,1)$ and $q=1-p$. The probability distribution of the sojourn time of the walk in the set of non-negative integers up to a fixed time is well-known, but its expression is not simple. By modifying slightly this sojourn time--through a particular counting process of the zeros of the walk as done by Chung & Feller ["On fluctuations in coin-tossings", Proc. Nat. Acad. Sci. U.S.A. 35 (1949), 605-608]-, simpler representations may be obtained for its probability distribution. In the aforementi…

关于布朗单局部时的随机积分及布朗单路径的正则化性质

Stochastic integration with respect to local time of the Brownian sheet and regularising properties of Brownian sheet paths

本研究将随机局部时空积分推广到布朗单情形，建立对应微积分体系，证明广义双参数Itô公式并推导Davie型不等式，为平均型算子的正则性界估计提供工具。

Weak convergence to the fractional Brownian sheet from a Lévy sheet

In this paper, we show an approximation in law, in the space of the continuous functions on $[0,1]^2$, of two-parameter Gaussian processes that can be represented as a Wiener type integral by processes constructed from processes that converge to the Brownian sheet. As an application, we obtain a sequence of processes constructed from a Lévy sheet that converges in law towards the fractional Brownian sheet.

Convergence to Weighted Fractional Brownian Sheets

We define weighted fractional Brownian sheets, which are a class of Gaussian random fields with four parameters that include fractional Brownian sheets as special cases, and we give some of their properties. We show that for certain values of the parameters the weighted fractional Brownian sheets are obtained as limits in law of occupation time fluctuations of a stochastic particle model. In contrast with some known approximations of fractional Brownian sheets which use a kernel in a Volterra type integral representation of fractional Brownian motion with respect to ordinary Brownian motion, o…

局部自相似高斯过程的逗留时间

Sojourns of locally self-similar Gaussian processes

本文针对局部自相似高斯过程，推导了有限时间区间上累积巴黎破产概率的精确渐近近似，并证明Berman常数可由不同于分数布朗运动的自相似过程定义。

Operator Fractional Brownian Sheet and Martingale Differences

In this paper, inspired by the fractional Brownian sheet of Riemann-Liouville type, we introduce the operator fractional Brownian sheet of Riemman-Liouville type, and study some properties of it. We also present an approximation in law to it based on the martingale differences.

Slices of Brownian Sheet: New Results, and Open Problems

We can view Brownian sheet as a sequence of interacting Brownian motions or slices. Here we present a number of results about the slices of the sheet. A common feature of our results is that they exhibit phase transition. In addition, a number of open problems are presented.

Approximation to multifractional Riemann-Liouville Brownian sheet

In this paper, we first introduce multifrational Riemann-Liouville Brownian sheets. Then, we show a result of approximation in law of the multifractional Riemann-Liouville Brownian sheet. The construction of these approximations is based on a sequence of I.I.D random variables.

Rate of convergence of uniform transport processes to Brownian sheet

In a previous paper we have constructed a family of processes, starting from a set of independent standard Poisson processes, that has realizations that converge almost surely to the Brownian sheet, uniformly in the unit square. Now, a rate of convergence from these processes to Brownian sheet is given.

From random partitions to fractional Brownian sheets

We propose discrete random-field models that are based on random partitions of $\mathbb{N}^2$. The covariance structure of each random field is determined by the underlying random partition. Functional central limit theorems are established for the proposed models, and fractional Brownian sheets, with full range of Hurst indices, arise in the limit. Our models could be viewed as discrete analogues of fractional Brownian sheets, in the same spirit that the simple random walk is the discrete analogue of the Brownian motion.

Example of a Gaussian self-similar field with stationary rectangular increments that is not a fractional Brownian sheet

We consider anisotropic self-similar random fields, in particular, the fractional Brownian sheet. This Gaussian field is an extension of fractional Brownian motion. We prove some properties of covariance function for self-similar fields with rectangular increments. Using Lamperti transformation we obtain properties of covariance function for the corresponding stationary fields. We present an example of a Gaussian self-similar field with stationary rectangular increments that is not a fractional Brownian sheet.

Weak approximation of the complex Brownian sheet from a Lévy sheet and applications to SPDEs

We consider a Lévy process in the plane and we use it to construct a family of complex-valued random fields that we show to converge in law, in the space of continuous functions, to a complex Brownian sheet. We apply this result to obtain weak approximations of the random field solution to a semilinear one-dimensional stochastic heat equation driven by the space-time white noise.

Kirillov-Frenkel character formula for Loop groups, radial part and Brownian sheet

We consider the coadjoint action of a Loop group of a compact group on the dual of the corresponding centrally extended Loop algebra and prove that a Brownian motion in a Cartan subalgebra conditioned to remain in an affine Weyl chamber - which can be seen as a space time conditioned Brownian motion - is distributed as the radial part process of a Brownian sheet on the underlying Lie algebra.

Convergence of finite-dimensional laws of the weighted quadratic variations process for some fractional Brownian sheets

In this paper we state and prove a central limit theorem for the finite-dimensional laws of the quadratic variations process of certain fractional Brownian sheets. The main tool of this article is a method developed by Nourdin and Nualart based on the Malliavin calculus.

由布朗单驱动的系统的马尔可夫性质

Markov property for systems driven by the Brownian sheet

本文针对布朗单驱动的双参数随机系统，提出并证明了由状态及其两个偏导数组成的三元组满足自然马尔可夫性质，并通过示例和Girsanov定理扩展至带漂移情形。

Asymptotic analysis via Mellin transforms for small deviations in $L^2$-norm of integrated Brownian sheets

We use Mellin transforms to compute a full asymptotic expansion for the tail of the Laplace transform of the squared $L^2$-norm of any multiply-integrated Brownian sheet. Through reversion we obtain corresponding strong small-deviation estimates.

On the distribution of maximum of a Brownian sheet restricted to a lower-dimensional set

We obtain sufficient conditions of stochastic equivalence of Gaussian random fields with special covariance function. These results generalize Doob's transformation (condition of stochastic equivalence of a Gaussian and a Wiener processes) to the case of random fields (condition of stochastic equivalence of a Gaussian process and a Brownian sheet). We look at the problem of finding the distribution of supremum of a Brownian sheet on a set with a dimension lower than the dimension of the field. We consider the probability of a Brownian sheet with a certain drift to attain zero level. The obtain…

Random walk local time approximated by a Wiener sheet combined with an independent Brownian motion

Let $ξ(k,n)$ be the local time of a simple symmetric random walk on the line. We give a strong approximation of the centered local time process $ξ(k,n)-ξ(0,n)$ in terms of a Wiener sheet and an independent Wiener process, time changed by an independent Brownian local time. Some related results and consequences are also established.

Critical Brownian sheet does not have double points

We derive a decoupling formula for the Brownian sheet which has the following ready consequence: An $N$-parameter Brownian sheet in $\mathbf{R}^d$ has double points if and only if $d<4N$. In particular, in the critical case where $d=4N$, the Brownian sheet does not have double points. This answers an old problem in the folklore of the subject. We also discuss some of the geometric consequences of the mentioned decoupling, and establish a partial result concerning $k$-multiple points in the critical case $k(d-2N)=d$.

Hausdorff dimension of the boundary of bubbles of additive Brownian motion and of the Brownian sheet

We first consider the additive Brownian motion process $(X(s_1,s_2),\ (s_1,s_2) \in \mathbb{R}^2)$ defined by $X(s_1,s_2) = Z_1(s_1) - Z_2 (s_2)$, where $Z_1$ and $Z_2 $ are two independent (two-sided) Brownian motions. We show that with probability one, the Hausdorff dimension of the boundary of any connected component of the random set $\{(s_1,s_2)\in \mathbb{R}^2: X(s_1,s_2) >0\}$ is equal to $$ \frac{1}{4}\left(1 + \sqrt{13 + 4 \sqrt{5}}\right) \simeq 1.421\, . $$ Then the same result is shown to hold when $X$ is replaced by a standard Brownian sheet indexed by the nonnegative quadrant.

An invariance principle for fractional Brownian sheets

We establish a central limit theorem for partial sums of stationary linear random fields with dependent innovations, and an invariance principle for anisotropic fractional Brownian sheets. Our result is a generalization of the invariance principle for fractional Brownian motions by Dedecker et al. (2011) to high dimensions. A key ingredient of their argument, the martingale approximation, is replaced by an m-approximation argument. An important tool of our approach is a moment inequality for stationary random fields recently established by El Machkouri et al. (2011).

Brownian sheet and time inversion -- From $G$-orbit to $L(G)$-orbit

We have proved in a previous paper that a space-time Brownian motion conditioned to remain in a Weyl chamber associated to an affine Kac-Moody Lie algebra is distributed as the radial part process of a Brownian sheet on the compact real form of the underlying finite dimensional Lie algebra, the radial part being defined considering the coadjoint action of a loop group on the dual of a centrally extended loop algebra. We present here a very brief proof of this result based on a time inversion argument and on elementary stochastic differential calculus.

Brownian sheet and reflectionless potentials

The bijectivity of the mapping, which is represented as expectation, from a family of Gaussian measures parametrized by linear combinations of Dirac measures to the space of classical reflectionless potentials is shown. It is also shown that the bijectivity extends to the space of generalized reflectionless potentials, which was used by V. Marchenko to study the Cauchy problem for the KdV equation. In the extension, the stochastic calculus based on the Brownian sheet plays a key role.

Strong approximations of Brownian sheet by uniform transport processes

Many years ago, Griego, Heath and Ruiz-Moncayo proved that it is possible to define realizations of a sequence of uniform transform processes that converges almost surely to the standard Brownian motion, uniformly on the unit time interval. In this paper we extend their results to the multi parameter case. We begin constructing a family of processes, starting from a set of independent standard Poisson processes, that has realizations that converge almost surely to the Brownian sheet, uniformly on the unit square. At the end the extension to the $d$-parameter Wiener processes is presented.

由时空布朗单驱动的McKean-Vlasov随机偏微分方程的Fokker-Planck方程

Fokker-Planck equation for McKean-Vlasov SPDEs driven by time-space Brownian sheet

本文研究由时空布朗单驱动的McKean-Vlasov型SPDE，证明混沌传播、非线性方程解的存在唯一性，并建立其解律的Fokker-Planck方程。

Brownian Sheet and Quasi-Sure Analysis

We present a self-contained and modern survey of some existing quasi-sure results via the connection to the Brownian sheet. Among other things, we prove that quasi-every continuous function: (i) satisfies the local law of the iterated logarithm; (ii) has Levy's modulus of continuity for Brownian motion; (iii) is nowhere differentiable; and (iv) has a nontrivial quadratic variation. We also present a hint of how to extend (iii) to obtain a quasi-sure refinement of the M. Csorgo--P. Revesz modulus of continuity for almost every continuous function along the lines suggested by M. Fukushima.

Brownian Sheet 的零点

Zeros of the Brownian Sheet

本文回答了 Khoshnevisan 的开放问题，证明了几乎必然不存在足够大秩的投影能改变 Brownian sheet 零点的 Hausdorff 维数，且不满足条件的投影将零点集映射为整个射影空间。

一种由时空布朗 sheet 驱动的线性系统的卡尔曼滤波器

A Kalman filter for linear systems driven by time-space Brownian sheet

针对由时空布朗 sheet 驱动的线性随机微分方程描述的信号与观测过程的滤波问题，推导了对应经典卡尔曼滤波器的时空类比随机积分方程，并通过含噪观测示例验证结果。

On eigenvalues of the Brownian sheet matrix

We derive a system of stochastic partial differential equations satisfied by the eigenvalues of the symmetric matrix whose entries are the Brownian sheets. We prove that the sequence $\left\{L_{d}(s,t), (s,t)\in[0,S]\times [0,T]\right\}_{d\in\mathbb N}$ of empirical spectral measures of the rescaled matrices is tight on $C([0,S]\times [0,T], \mathcal P(\mathbb R))$ and hence is convergent as $d$ goes to infinity by Wigner's semicircle law. We also obtain PDEs which are satisfied by the high-dimensional limiting measure.

The Large Deviation of Semilinear Stochastic Partial Differential Equation Driven by Brownian Sheet

We prove the the large deviation principle(LDP) for the law of the one-dimensional semilinear stochastic partial differential equations driven by nonlinear multiplicative noise. Firstly, combining the energy estimate and approximation procedure, we obtain the existence of global solution. Then the large deviation principle is obtained via weak convergence method.

Image sets of fractional Brownian sheets

Let $B^H = \{ B^H(t), t\in\mathbb{R}^N \}$ be an $(N,d)$-fractional Brownian sheet with Hurst index $H=(H_1,\dotsc,H_N)\in (0,1)^N$. The main objective of the present paper is to study the Hausdorff dimension of the image sets $B^H(F+t)$, $F\subset\mathbb{R}^N$ and $t\in\mathbb{R}^N$, in the dimension case $d<\tfrac{1}{H_1}+\cdots+\tfrac{1}{H_N}$. Following the seminal work of Kaufman (1989), we establish uniform dimensional properties on $B^H$, answering questions raised by Khoshnevisan et al (2006) and Wu and Xiao (2009). For the purpose of this work, we introduce a refinement of the sectori…

Multiple points of the Brownian sheet in critical dimensions

It is well known that an $N$-parameter $d$-dimensional Brownian sheet has no $k$-multiple points when $(k-1)d>2kN$, and does have such points when $(k-1)d<2kN$. We complete the study of the existence of $k$-multiple points by showing that in the critical cases where $(k-1)d=2kN$, there are a.s. no $k$-multiple points.

Hermite variations of the fractional Brownian sheet

We prove central and non-central limit theorems for the Hermite variations of the anisotropic fractional Brownian sheet $W^{α, β}$ with Hurst parameter $(α, β) \in (0,1)^2$. When $0<α\leq 1-\frac{1}{2q}$ or $0<β\leq 1-\frac{1}{2q}$ a central limit theorem holds for the renormalized Hermite variations of order $q\geq 2$, while for $1-\frac{1}{2q}<α, β< 1$ we prove that these variations satisfy a non-central limit theorem. In fact, they converge to a random variable which is the value of a two-parameter Hermite process at time $(1,1)$.

布朗片的击中概率、热容量与豪斯多夫维数结果

Hitting probabilities, thermal capacity, and Hausdorff dimension results for the Brownian sheet

该论文研究布朗片击中紧集的概率与交集维数，给出正概率相交的充要条件，并以热容量刻画交集豪斯多夫维数的本质确界，推广了布朗运动及区间情形下的已有结果。

分数布朗运动驱动SDEs的强解

Strong solutions of fractional Brownian sheet driven SDEs with integrable drift

本文研究了由Hurst参数小于1/2的分数布朗运动驱动的随机微分方程的强解存在性，利用Malliavin微积分和扇形局部非确定性理论证明了唯一可微强解的存在。

Stochastic Stefan Problems Driven By Standard Brownian Sheets

In this paper we study the effect of stochastic perturbations on a common type of moving boundary value PDE's which endorse Stefan boundary conditions, or Stefan problems, and show the existence and uniqueness of the solutions to a number of stochastic equations of this kind. Moreover we also derive the space and time regularities of the solutions and the associated boundaries via Kolmogorov's Continuity Theorem in an appropriately defined normed space. The paper first conveys our previous results where randomness is smoothly correlated in space and Brownian in time, then introduces a new meth…

Lévy过程正停留时间的Poisson表示

A Poisson representation of the positive sojourn time of Lévy processes

本文研究任意Lévy过程的正停留时间，利用独立指数时刻证明其可表示为强度由正性函数给出的Poisson过程点之和，并推导双重Laplace变换及反正弦定律的新结果。

通过两个分数布朗运动片对双曲随机偏微分方程进行正则化

Regularization of Hyperbolic Stochastic Partial Differential Equations By Two Fractional Brownian Sheets

本文通过两个相关分数布朗运动片对双曲随机偏微分方程进行正则化，证明了在弱假设下方程的强解存在性和唯一性。

Joint continuity of the local times of fractional Brownian sheets

Let $B^H=\{B^H(t),t\in{\mathbb{R}_+^N}\}$ be an $(N,d)$-fractional Brownian sheet with index $H=(H_1,...,H_N)\in(0,1)^N$ defined by $B^H(t)=(B^H_1(t),...,B^H_d(t)) (t\in {\mathbb{R}}_+^N),$ where $B^H_1,...,B^H_d$ are independent copies of a real-valued fractional Brownian sheet $B_0^H$. We prove that if $d<\sum_{\ell=1}^NH_{\ell}^{-1}$, then the local times of $B^H$ are jointly continuous. This verifies a conjecture of Xiao and Zhang (Probab. Theory Related Fields 124 (2002)). We also establish sharp local and global Hölder conditions for the local times of $B^H$. These results are applied to…

Functional limit theorems for generalized variations of the fractional Brownian sheet

We prove functional central and non-central limit theorems for generalized variations of the anisotropic $d$-parameter fractional Brownian sheet (fBs) for any natural number $d$. Whether the central or the non-central limit theorem applies depends on the Hermite rank of the variation functional and on the smallest component of the Hurst parameter vector of the fBs. The limiting process in the former result is another fBs, independent of the original fBs, whereas the limit given by the latter result is an Hermite sheet, which is driven by the same white noise as the original fBs. As an applicat…

Stochastic evolution equations for nonlinear filtering of random fields in the presence of fractional Brownian sheet observation noise

The problem of nonlinear filtering of a random field observed in the presence of a noise, modeled by a persistent fractional Brownian sheet of Hurst index $(H_1,H_2)$ with $0.5<H_1,H_2<1$, is studied and a suitable version of the Bayes' formula for the optimal filter is obtained. Two types of spatial "fractional" analogues of the Duncan-Mortensen-Zakai equation are also derived: one tracks evolution of the unnormalized optimal filter along an arbitrary "monotone increasing" (in the sense of partial ordering in $\mathbb{R}^2$) one-dimensional curve in the plane, while the other describes dynami…

具有随机漂移和不同布朗时钟的广义计数过程

Generalized Counting Process with Random Drift and Different Brownian Clocks

本文引入了具有确定性和随机漂移的广义计数过程（GCP），推导了其概率律和分数阶微分方程，并研究了在多种布朗时钟及不完全伽马函数相关从属过程下的时间变更GCP及其分数阶积分。

Images of the Brownian Sheet

An N-parameter Brownian sheet in R^d maps a non-random compact set F in R^N_+ to the random compact set B(F) in \R^d. We prove two results on the image-set B(F): (1) It has positive d-dimensional Lebesgue measure if and only if F has positive (d/2)-dimensional capacity. This generalizes greatly the earlier works of J. Hawkes (1977), J.-P. Kahane (1985a; 1985b), and one of the present authors (1999). (2) If the Hausdorff dimension of F is strictly greater than (d/2), then with probability one, we can find a finite number of points ζ_1,...,ζ_m such that for any rotation matrix θthat leaves F in …

布朗片驱动系统的最优停止

Optimal Stopping for Systems Driven by the Brownian Sheet

本文研究了由布朗片驱动的系统最优停止问题，通过推导两个显式解，确定了最优停止阈值，并建立了潜在理论框架以证明价值函数的性质。

Brownian Sheet Images and Bessel-Riesz Capacity

We show that the image of a 2-dimensional set under d-dimensional, 2-parameter Brownian sheet can have positive Lebesgue measure, if and only if the set in question has positive (d/2)-dimensional Bessel-Riesz capacity. Our methods solve a problem of J.-P. Kahane.

Path regularity of Brownian motion and Brownian sheet

By the work of P. Lévy, the sample paths of the Brownian motion are known to satisfy a certain Hölder regularity condition almost surely. This was later improved by Ciesielski, who studied the regularity of these paths in Besov and Besov-Orlicz spaces. We review these results and propose new function spaces of Besov type, strictly smaller than those of Ciesielski and Lévy, where the sample paths of the Brownian motion lie in almost surely. In the same spirit, we review and extend the work of Kamont, who investigated the same question for the multivariate Brownian sheet and function spaces of d…

The number of cycles in a random permutation and the number of segregating sites jointly converge to the Brownian sheet

Consider a random permutation of $\{1, \ldots, \lfloor n^{t_2}\rfloor\}$ drawn according to the Ewens measure with parameter $t_1$ and let $K(n, t)$ denote the number of its cycles, where $t\equiv (t_1, t_2)\in\mathbb [0, 1]^2$. Next, consider a sample drawn from a large, neutral population of haploid individuals subject to mutation under the infinitely many sites model of Kimura whose genealogy is governed by Kingman's coalescent. Let $S(n, t)$ count the number of segregating sites in a sample of size $\lfloor n^{t_2}\rfloor$ when mutations arrive at rate $t_1/2$. Our main result comprises tw…

Scaling limits of discrete copulas are bridged Brownian sheets

For large $n$, take a random $n \times n$ permutation matrix and its associated discrete copula $X_n$. For $a, b = 0, 1, \ldots, n$, let $y_n(\frac{a}{n},\frac{b}{n}) = \frac{1}{n} ( X_{a,b} - \frac{ab}{n} )$; define $y_n: [0,1]^2 \to R$ by interpolating quadratically on squares of side $\frac{1}{n}$. We prove a Donsker type central limit theorem: $\sqrt{n} y_n$ approaches a bridged Brownian sheet on the unit square.

由布朗单驱动的条件 McKean-Vlasov 系统的 Fokker-Planck 方程

Fokker-Planck equations for conditional McKean-Vlasov systems driven by Brownian sheets

本文研究由时空白噪声驱动的条件 McKean-Vlasov 方程，建立解的存在唯一性并推导条件律的积分型随机 Fokker-Planck 方程，进而应用于部分观测控制问题。

Low regularity solutions to the stochastic geometric wave equation driven by a fractional Brownian sheet

We announce a result on the existence of a unique local solution to a stochastic geometric wave equation on the one dimensional Minkowski space $\mathbb{R}^{1+1}$ with values in an arbitrary compact Riemannian manifold. We consider a rough initial data in the sense that its regularity is lower than the energy critical.

Linear Multifractional Stable Sheets in the Broad Sense: Existence and Joint Continuity of Local Times

We introduce the notion of linear multifractional stable sheets in the broad sense (LMSS) with $α\in(0,2]$, to include both linear multifractional Brownian sheets ($α=2$) and linear multifractional stable sheets ($α<2$). The purpose of the present paper is to study the existence and joint continuity of the local times of LMSS, and also the local Hölder condition of the local times in the set variable. Among the main results of this paper, Theorem 2.4 provides a sufficient and necessary condition for the existence of local times of LMSS; Theorem 3.1 shows a sufficient condition for the joint co…

Local times of multifractional Brownian sheets

Denote by $H(t)=(H_1(t),...,H_N(t))$ a function in $t\in{\mathbb{R}}_+^N$ with values in $(0,1)^N$. Let $\{B^{H(t)}(t)\}=\{B^{H(t)}(t),t\in{\mathbb{R}}^N_+\}$ be an $(N,d)$-multifractional Brownian sheet (mfBs) with Hurst functional $H(t)$. Under some regularity conditions on the function $H(t)$, we prove the existence, joint continuity and the Hölder regularity of the local times of $\{B^{H(t)}(t)\}$. We also determine the Hausdorff dimensions of the level sets of $\{B^{H(t)}(t)\}$. Our results extend the corresponding results for fractional Brownian sheets and multifractional Brownian motion…

Path-by-path uniqueness of multidimensional SDE's on the plane with nondecreasing coefficients

In this paper we study path-by-path uniqueness for multidimensional stochastic differential equations driven by the Brownian sheet. We assume that the drift coefficient is unbounded, verifies a spatial linear growth condition and is componentwise nondeacreasing. Our approach consists of showing the result for bounded and componentwise nondecreasing drift using both a local time-space representation and a law of iterated logarithm for Brownian sheets. The desired result follows using a Gronwall type lemma on the plane. As a by product, we obtain the existence of a unique strong solution of mult…

Gaussian fluctuation for spatial average of super-Brownian motion

Let $\{u(t\,, x)\}_{(t, x)\in \mathbb{R}_+\times \mathbb{R}}$ be the density of one-dimensional super-Brownian motion starting from Lebesgue measure. Using the Laplace functional of super-Brownian motion, we prove that as $N\to \infty$, the normalized spatial integral $N^{-1/2}\int_0^{xN}[u(t\,, z)-1 ]\rm{d} z$ converges jointly in $(t, x)$ to Brownian sheet in distribution.