Questions related to Brownian motion, a continuous stochastic process denoted by $W_t$, $t\geq 0$, with independent increments, such that $W(t)-W(s)$ is normally distributed, with $0$ mean and variance $t-s$.

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68 views

Proving how to reduce a Brownian walk on a plane to a line (2D to 1D)

I have a Brownian motion on a plane and would like to find the time of when it is expected to hit a set of parallel lines, i.e the hitting time. In order to do so, I understand that I can reduce the ...
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35 views

Brownian motion - independence

I have not so difficult task - For Brownian motion $W(s)-W(t)$ is independant of $\sigma$-algebra $F(t)$ $0\leq t<s$. My goal is to show that for $0\leq t<s<u$, $W(u)-W(s)$ is also ...
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1answer
20 views

What is a general Brownian Motion?

This might be a dumb question, but no textbook ever defines what a "Brownian Motion" is, just what a "Standard Brownian Motion." I always assumed that a Brownian Motion is any random variable that can ...
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0answers
29 views

Brownian motion checking

$W(t)$ is a Brownian motion and $c>0$. I need to verify that 1)$X(t)=W(c+t)-W(c)$ and $X(t)=cW(t/c^2)$ are Brownian motions. 2) $Z(t)=tW(1/t)$ can be showm as $lim_{t-\rightarrow\infty} Z(t)=0$....
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2answers
44 views

If $B_t$ is a standard brownian motion process, is $B_t^2 - \frac{t}{2}$ a martingale w.r.t. brownian motion?

If I have that $B_t$ is a standard brownian motion process, is $B_t^2 - \frac{t}{2}$ a martingale w.r.t. brownian motion? I know that $B_t^2 - t$ is but can't see it for the latter.
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0answers
14 views

Showing time inversion of a Brownian Motion $X_t = tB_{1/t}$ is continuous at $t=0$ USING the fact $X_t$ is BM on $\mathbb{Q}$? [duplicate]

I am reading the following paper on a rigorous construction of Brownian Motion: Brownian Motion. In the paper, they give a peculiar proof of the fact that the time inverted Brownian Motion is ...
0
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1answer
44 views

If $B_t$ is standard Brownian Motion, how to show that $X_t = B_t^2-t$ is a martingale?

If $(B_t, \mathcal{F}_t)$ is standard Brownian Motion, I would like to show that $X_t = B_t^2-t$ is a martingale. My attempted proof works as follows: \begin{align} E(X_{t+1}|\mathcal{F}_t) & = E(...
0
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0answers
44 views

For Brownian Motion $B_t$, and stop time $\nu = \inf\{t: B_t = r\}$, how to show $E(e^{-\alpha\nu}) = e^{-|r|\sqrt{2\alpha}}$?

If we have that $B_t$ is a Brownian Motion process, and we define a hitting time as $\nu = \inf\{t: B_t = r\}$ where $r \in \mathbb{R}$, how can I show that: $$ E(e^{-\alpha\nu}) = e^{-|r|\sqrt{2\...
4
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1answer
35 views

Is the Hölder random constant of the Brownian Motion Integrable?

Let $\{B_t:t\in [0,1]\}$ be the standard one-dimensional Brownian motion on the closed unit interval. Fix $\gamma\in (0,1/2)$. It is well known that there is a positive random variable $K\equiv K(\...
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1answer
35 views

Change of variable in $\varphi(s) = t$, effect in $\mathbb{d} W_t$

I'm a little confused here. If I have the stochastic integral $$ \int_0^T f(t)\,\mathbb{d} W_t $$ and perform the change of variables $t = \varphi(s)$, how will $\mathbb{d} W_t$ transform (where the ...
4
votes
1answer
124 views

Solution for SDE: $dF_t= \beta_t\left(F_t - \alpha\right)dW_t$

I am trying to derive the solution for the following stochastic differential equation, but I must be doing something wrong in my calculations because I can't arrive to the correct solution. The SDE ...
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1answer
33 views

Modification of Donsker Theorem

assume some i.i.d. random variables $(X_i)_{i \geq 1}$ with mean 0 and variance 1. Due to Donsker it holds that $$\left(\frac{1}{\sqrt{n}}\sum\limits_{i=1}^{nt}{X_i}\right)_t \rightarrow (W_t)_t$$ ...
0
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0answers
54 views

Variance of Brownian Integral when the end point is specified

Consider the Brownian $W_u$. Suppose you are only considering realizations of this brownian that verify both $W_0=0$ and, for a specific (given) $t$, $W_t=a$. Under these specific conditions, what is ...
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0answers
22 views

harmonic measure circle

I'm trying to compare the probability of a particle (performing Brownian Motion), starting a large distance away from a circle, passing through a specific section of that circle is approximately the ...
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0answers
36 views

Transience of Brownian Motion

I am reading a book by Morters & Peres on Brownian motion, and I got really confused with the definition of transience. At first, they give a simple definition that BM is transient if it converges ...
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1answer
49 views

Calculate $E[\exp(iu\int_0^ts \, dB_s)]$ for a Brownian motion $(B_t)_{t \geq 0}$

Since $X_t:=\int_0^ts \, dB_s$ is a process with independent increments, its distribution is infinitely divisible and its variance is $c_t=\frac{1}{3}t^3$. I think, its characteristic function $E[\...
1
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1answer
60 views

Itos formula on a transformation of bessel Processes

Let $W$ be a Brownian motion and $z,\kappa>0$. Let $X_t(z)$ be a solution to the SDE $$dX_t(z)=dW_t+2/(\kappa X_t(z))dt.\quad X_0(z)=z.$$ The solution is well-defined on $t<\tau(z)$ where $\...
5
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2answers
150 views

The stochastic integral $\int W_t dW_t$

I'm reading an introduction to Stochastic Calculus. I'm at the point where Ito integrals are developed and constrasted with the Stratonovich integral. Below is a calculation of $\int_0^T W_t d W_t$. ...
3
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0answers
45 views

Holder Continuity of a Continuous Stochastic Process

I have recently read the proof that the Brownian Motion and Fractional Brownian motion are almost surely Holder Continuous. I was wondering if this can be extended to a higher class of continuous ...
2
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1answer
87 views

Proving that stopped Brownian motions has a limit.

Assume that $(\tau_n)$,$(T_n)$ are finite strictly increasing stopping times and set $\tau=\sup_{n}\tau_n$,$T=\sup_{n}T_n$. Now consider a process $(W_t)_{t<\tau}$, and a Brownian motion $B$, which ...
3
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1answer
57 views

Gaussian process with independent increments

Suppose that we have a continuous Gaussian process $(X_t)_{t \ge 0}$ with independent increments and $X_0=0$. If the increments are also identically distributed, meaning that $X_b-X_a \stackrel{D}{=} ...
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0answers
27 views

Brownian motion through gates

Exercise 1.9.6 of Ubbo F. Wiersema's textbook "Brownian Motion Calculus" (Wiley 2008, p. 27) is titled "Brownian motion through gates" and begins: "Consider a Brownian motion path that passes through ...
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1answer
26 views

I want to simplify the stochastic integral by change variable

Let $f:[0,t]\rightarrow \mathbb{R^+}$ be a deterministic and integrable and $(B_t)_{t\geq 0}$ is a standard Brownian motion. If $X_t=\int_o^tf(s)dB_s$, we know that $X_t$ has normal distribution with ...
2
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0answers
40 views

Can a time-shifted Brownian motion be also a Brownian motion

Let $T<\infty$, $(\Omega,\mathcal F,P)$ a probability space carrying a standard $d$-dimensional Brownian motion $(B_t)_{t\geq 0}$ and $(\mathcal F_t)_{t\geq 0}$ the natural $\sigma$-algebra ...
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0answers
8 views

Finding a probability measure such that the time-shifted Brownian motion is also a Brownian motion [duplicate]

Let $T<\infty$, $(\Omega,\mathcal F,P)$ a probability space carrying a standard $d$-dimensional Brownian motion $(B_t)_{t\geq 0}$ and $(\mathcal F_t)_{t\geq 0}$ the natural $\sigma$-algebra ...
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0answers
27 views

Probability Reference Request

Right now I am studying probability theory and I am looking for a string of related books that will cover topics through Stochastic Calculus. More explicitly, I am hoping to self study Stochastic ...
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0answers
22 views

1D Brownian motion: stopping time and stopping state not independent

I am trying to learn Brownian motion on my own and attempting some exercises. Let ${X_t}$ be a standard 1D Brownian motion and define $$T=\inf \{t:X_t=1 \ or \ -3 \}$$ The question is: show that $...
0
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1answer
31 views

Exponential of Sums of different times of a Brownian Motion

Let $\{B_s\}_{s\in[0,1]}$ be a Brownian motion, let $t_1 < \dots < t_n \in [0,1]$, I am interested in finding good upper and lower bounds for $$ \mathbb{E}[\exp(B_{t_1}+ \dots + B_{t_n})]. $$ ...
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0answers
22 views

What will be the behavior of $R(t)$ if $R(0)=\alpha / \beta$ in Vasicek model

Can someone please help explain what the behavior of $R(t) = \alpha / \beta$ would be if $dR(t)=(\alpha-\beta R(t))dt +\sigma dW(t)$ I already know the expression for R(t) and I know the mean and ...
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1answer
43 views

If given the Vasicek Interest rate model $dR(t)=(\alpha-\beta R(t))dt +\sigma dW(t)$ how do I use Ito's lemma to find $d(e^{\beta t}R(t))$?

If given the Vasicek Interest rate model $dR(t)=(\alpha-\beta R(t))dt +\sigma dW(t)$ how do I use Ito's lemma to find $d(e^{\beta*t}R(t))$ and simplify so it is a solution that does not include R(t). ...
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1answer
50 views

Check that an Ito integral is a martingale.

Before presenting my problem I will introduce some notation. Time index $t\in [0,T]$. $$C_t = \begin{cases} Z_n = B_{t_{n-1}}, & \text{if $t=T$} \\[2ex] Z_i = B_{t_{i-1}} , & \text{if $t_{i-...
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0answers
33 views

Independence of Brownian motions

Let $W_t$ be a Brownian motion at time $t$ and let $t<t_1<T$. I'm trying to find the variance of $$ k\sigma W_{t_1} + \sigma \left(W_T - W_t\right).$$ I started by letting $$ k\sigma W_{t_1} + \...
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1answer
43 views

Variance of integral

I am trying to understand stochastic calculus and got stuck calculating the following. I need the distribution of a zero bond under the black model, so I am deriving the variance using the second ...
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1answer
51 views

Scaling property for Brownian motion [closed]

Define Brownian motion as a continuous process $(B_t)$ with independent increments, such that $B_{s+t}-B_{s}$ has normal distribution with mean $0$ and variance $t$. How do you use the independence of ...
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1answer
39 views

Fubini's theorem for Stochastic Integral, with sum

I am struggling here with part (2), . In usual instances, I've had the question phrased like this but I'm not sure how to deal with the summation?
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2answers
34 views

Prove that Brownian motion $(X_t)$ is such that $P(|X_{t+h} − X_t|> ε)\ll h$ when $h\to 0$

I am facing this problem, but don't have the knowledge to solve it. I need to prove that given a simple Brownian motion $X_t$, I have that $$\frac{P(|X_{t+h} − X_t|> ε)}{h}→ 0 \mbox{ when }h\to 0.$...
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0answers
12 views

Question about Brownian motion invariance

We know that if $(W_s)$ is a Brownian motion, then $W_{s+T}-W_T$ is a Brownian motion where T >0. So $W_{s+T}=(W_{s+T}-W_T)+W_T$ is the sum of a Brownian motion and a time-independent process. In my ...
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0answers
28 views

First hitting time of an open set

I am trying to go through the problems in Shreve & Oksendal, this is the problem 2.6 Prove that the first hitting time $\tau$ of $A$ an open subset of $\mathcal{B}(\mathbb{R}^d)$ is an optional ...
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1answer
87 views

I've found two different definitions of a cylindrical Brownian motion and don't understand why they are consistent

Let $(\Omega,\mathcal A,\operatorname P)$ be a probability space $(\mathcal F_t)_{t\ge 0}$ be a filtration of $\mathcal A$ $(U,\langle\;\cdot\;,\;\cdot\;\rangle)$ be a separable Hilbert space $\left(...
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0answers
49 views

Prove of the existence of a cylindrical Brownian motion

Let $(\Omega,\mathcal A,\operatorname P)$ be a probability space $(\mathcal F_t)_{t\ge 0}$ be a filtration of $\mathcal A$ $(U,\langle\;\cdot\;,\;\cdot\;\rangle)$ be a separable Hilbert space $Q$ be ...
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0answers
50 views

Can we prove/disprove that Brownian motion is nowhere differentiable in $L^2$?

I have read the proof that Brownian motion is a.s. nowhere differentiable. However can we construct a proof that Brownian motion is no where differentiable in $L^2$ for an appropriate definition of $...
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0answers
25 views

Representation formula for a Hilbert space valued Brownian motion. Prove independence of the real-valued Brownian motions in the expansion.

Let $(\Omega,\mathcal A,\operatorname P)$ be a probability space $(\mathcal F_t)_{t\ge 0}$ be a filtration of $\mathcal A$ $(U,\langle\;\cdot\;,\;\cdot\;\rangle)$ be a separable Hilbert space $Q$ be ...
2
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0answers
25 views

If a Stochastic Process has Variance linear with t, how to prove it is not Wide Sense Stationary?

For my study, as a part of a Matlab exercise, the following question is asked: Using the results of the estimated standard deviations of the random variable $x(k)$ for $k = 10^3; 10^4; 10^5$ ...
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0answers
43 views

$ \lim\limits_{n\rightarrow \infty} {\frac{B_{t}}{t}}$ Brownian Motion

I want to prove in two ways that $ \lim\limits_{n\rightarrow \infty} {\frac{B_{t}}{t}}\rightarrow 0$ almost surely, where $B_{t}$ is a standard Brownian Motion. 1) in $L^2$ Can we say $X_{t}={\...
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0answers
13 views

Why is there periodicity in the output of Richard Voss' fractional Brownian motion?

I am trying to figure out why the output of fractional Brownian motion (fBm) as described by Richard Voss (Random fractal forgeries. In: Fundamental Algorithms for Computer Graphics, R. A. Earnshaw (...
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1answer
21 views

Martingale $c^{W_t}$ where $W$ is Brownian motion

I have the process $c^{W_{t}}$ where $c$ is a constant and $W$ is Brownian motion. I would like to check if $\mathbb E[c^{W_{t+1}}|F_t]=c^{W_t}$. Dividing the right site yield $\mathbb E[c^{W_{t+1}-...
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0answers
122 views

How to calculate the PSD of a stochastic process

Say we have a stochastic process described by a stochastic differential equation (in the Itô sense), and maybe we are able to find an explicit solution of it in terms of deterministic and Itô ...
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0answers
55 views

Correlated Brownian motions

Let $V$ and $W$ be Brownian motions such that $\mathbb{E}W_tV_t=\rho t$. Let $$R_t=\sup_{u \le t} V_u \mbox{ and } Z_t=\sup_{u \le t}W_u .$$ Show that $$\mathbb{E}R_tZ_t=tf(\rho) .$$ Can you find $f(...
1
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0answers
58 views

Generalised arcsine law of brownian motion

It is well known that for a standard brownian motion, the time spent above $0$ follows an arcsine distribution (whose density function is U-shaped). Can anyone tell me how to generalise this result to ...
1
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0answers
55 views

Range of a standard brownian motion, using reflection principle

With a standard brownian motion $B_t$, I'm trying to find the distribution of the "range": $$R_{t} = \sup_{0 \leq s \leq t} B_s - \inf_{0 \leq s \leq t} B_s = \overline{M_t}-\underline{M_t}$$ The ...