Small-time compactness and convergence behavior of deterministically and self-normalised Lévy processes

Author:

Maller Ross,Mason David

Abstract

Consider a Lévy process X t X_t with quadratic variation process V t = σ 2 t + 0 > s t ( Δ X s ) 2 V_t=\sigma ^2 t+ \sum _{0>s\le t} (\Delta X_s)^2 , t > 0 t>0 , where Δ X t = X t X t \Delta X_t=X_t-X_{t-} denotes the jump process of X X . We give stability and compactness results, as t 0 t\,\downarrow \,0 , for the convergence both of the deterministically normed (and possibly centered) processes X t X_t and V t V_t , as well as theorems concerning the “self-normalised” process X t / V t X_{t}/\sqrt {V_t} . Thus, we consider the stochastic compactness and convergence in distribution of the 2-vector ( ( X t a ( t ) ) / b ( t ) , V t / b ( t ) ) \left ((X_t-a(t))/b(t), V_t/b(t)\right ) , for deterministic functions a ( t ) a(t) and b ( t ) > 0 b(t)>0 , as t 0 t\,\downarrow \,0 , possibly through a subsequence; and the stochastic compactness and convergence in distribution of X t / V t X_{t}/\sqrt {V_t} , possibly to a nonzero constant (for stability), as t 0 t\,\downarrow \,0 , again possibly through a subsequence.

As a main application it is shown that X t / V t D N ( 0 , 1 ) X_{t}/\sqrt {V_t}\stackrel {\mathrm {D}}{\longrightarrow } N(0,1) , a standard normal random variable, as t 0 t\,\downarrow \,0 , if and only if X t / b ( t ) D N ( 0 , 1 ) X_t/b(t)\stackrel {\mathrm {D}}{\longrightarrow } N(0,1) , as t 0 t\downarrow 0 , for some nonstochastic function b ( t ) > 0 b(t)>0 ; thus, X t X_t is in the domain of attraction of the normal distribution, as t 0 t\,\downarrow \,0 , with or without centering constants being necessary (these being equivalent).

We cite simple analytic equivalences for the above properties, in terms of the Lévy measure of X X . Functional versions of the convergences are also given.

Publisher

American Mathematical Society (AMS)

Subject

Applied Mathematics,General Mathematics

Reference40 articles.

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3. Functional laws for trimmed Lévy processes;Journal of Applied Probability;2017-09

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5. Convergence of trimmed Lévy processes to trimmed stable random variables at 0;Stochastic Processes and their Applications;2015-10

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