Zooming-in conjecture at the maximal distance from the origin for Lévy processes

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Assume that the Lévy process XX has finite lifetime ζ(0,)\zeta\in(0,\infty). Let

τ:=sup{t0:max(Xt,Xt)=sups0Xs}\tau:=\sup\left\{t\geq 0:\max\left(\|X_t\|,\|X_{t-}\|\right)=\sup_{s\geq 0}\|X_s\|\right\}

be the last time at which the Euclidean norm is maximal. Set M:=XτM:=X_\tau if XτXτ\|X_\tau\|\geq\|X_{\tau-}\| and M:=XτM:=X_{\tau-} otherwise, and define the reversed and forward processes by

Xt:={X(τt)M,0t<τ,,tτ,Xt:={Xτ+tM,0t<ζτ,,tζτ.\overleftarrow{X}_t:=\begin{cases}X_{(\tau-t)-}-M,&0\leq t<\tau,\dagger,&t\geq\tau,\end{cases}\qquad \overrightarrow{X}_t:=\begin{cases}X_{\tau+t}-M,&0\leq t<\zeta-\tau,\dagger,&t\geq\zeta-\tau.\end{cases}

Let BB be the Brownian part of XX with a non-singular covariance matrix. Zooming-in conjecture at the maximal distance.

n(X/n,X/n)d(B,B),\sqrt{n}\bigl(\overleftarrow{X}_{\cdot/n},\overrightarrow{X}_{\cdot/n}\bigr)\xrightarrow{d}(-B^\Downarrow,B^\Uparrow),

where the limit pair is a mixture of (B,B)(-B^{\downarrow},B^{\uparrow}) for the independent direction η=M\eta=-M. This conjecture predicts a multidimensional analogue of the one-dimensional stable-convergence result for zooming in at an extremal time; proving it is described as exceedingly challenging, and the anticipated stable convergence is not included in the statement.

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Sources & referencesView supporting material

Primary source

Jevgenijs Ivanovs and Jakob D. Thøstesen, “Lévy processes conditioned to stay in a half-space with applications to directional extremes”, arXiv:2105.12539 (2021).

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