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Thomas Kojar
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Since we can apply Burkholder-Davis-Gundy to control the supremum of moments, we start by removing the tail simply using $1\leq \frac{|X_{t}|}{R}$.

$$ \mathbb E [ |X_t|^p 1_{\{|X_t| \ge R\}} ]\leq \frac{1}{R}\mathbb E [ |X_t|^{p+1} ]. $$

And then as done in René Schilling, Lothar Partzsch: Brownian Motion - An Introduction to Stochastic Processes, Chapter 19 (2nd edition) (see Application of the Burkholder Davis Gundy inequality) we have the bound

$$\sup_{t\leq T}\mathbb E [ |X_t|^{p+1} ]\leq \mathbb{E}\sup_{t\leq T}|X_t|^{p+1}\leq Ce^{CT}(1+\mathbb{E}|X_0|^{p+1}).$$

Interestingly, note that you can get faster decay by using $1\leq \frac{|X_{t}|^{q}}{R^{q}}$ if you have $\mathbb{E}|X_0|^{p+q}<\infty$.

Since we can apply Burkholder-Davis-Gundy to control the supremum of moments, we start by removing the tail simply using $1\leq \frac{|X_{t}|}{R}$.

$$ \mathbb E [ |X_t|^p 1_{\{|X_t| \ge R\}} ]\leq \frac{1}{R}\mathbb E [ |X_t|^{p+1} ]. $$

And then as done in René Schilling, Lothar Partzsch: Brownian Motion - An Introduction to Stochastic Processes, Chapter 19 (2nd edition) (see Application of the Burkholder Davis Gundy inequality) we have the bound

$$\sup_{t\leq T}\mathbb E [ |X_t|^{p+1} ]\leq \mathbb{E}\sup_{t\leq T}|X_t|^{p+1}\leq Ce^{CT}(1+\mathbb{E}|X_0|^{p+1}).$$

Since we can apply Burkholder-Davis-Gundy to control the supremum of moments, we start by removing the tail simply using $1\leq \frac{|X_{t}|}{R}$.

$$ \mathbb E [ |X_t|^p 1_{\{|X_t| \ge R\}} ]\leq \frac{1}{R}\mathbb E [ |X_t|^{p+1} ]. $$

And then as done in René Schilling, Lothar Partzsch: Brownian Motion - An Introduction to Stochastic Processes, Chapter 19 (2nd edition) (see Application of the Burkholder Davis Gundy inequality) we have the bound

$$\sup_{t\leq T}\mathbb E [ |X_t|^{p+1} ]\leq \mathbb{E}\sup_{t\leq T}|X_t|^{p+1}\leq Ce^{CT}(1+\mathbb{E}|X_0|^{p+1}).$$

Interestingly, note that you can get faster decay by using $1\leq \frac{|X_{t}|^{q}}{R^{q}}$ if you have $\mathbb{E}|X_0|^{p+q}<\infty$.

Source Link
Thomas Kojar
  • 5.5k
  • 2
  • 19
  • 41

Since we can apply Burkholder-Davis-Gundy to control the supremum of moments, we start by removing the tail simply using $1\leq \frac{|X_{t}|}{R}$.

$$ \mathbb E [ |X_t|^p 1_{\{|X_t| \ge R\}} ]\leq \frac{1}{R}\mathbb E [ |X_t|^{p+1} ]. $$

And then as done in René Schilling, Lothar Partzsch: Brownian Motion - An Introduction to Stochastic Processes, Chapter 19 (2nd edition) (see Application of the Burkholder Davis Gundy inequality) we have the bound

$$\sup_{t\leq T}\mathbb E [ |X_t|^{p+1} ]\leq \mathbb{E}\sup_{t\leq T}|X_t|^{p+1}\leq Ce^{CT}(1+\mathbb{E}|X_0|^{p+1}).$$