Large deviations for light-tailed L\'evy bridges on short time scales

TL;DR

This paper establishes a large deviations principle for the bridges of scaled multivariate Le9vy processes with light tails, revealing the most probable path and analyzing jump behavior on short time scales.

Contribution

It provides the first large deviations analysis for Le9vy process bridges under short time scaling with light tails, including path, jump, and normality results.

Findings

Linear path between start and end points is the most probable

Exponential negligibility of paths deviating from the straight line

Asymptotic normality of jump increments

Abstract

Let $L = (L(t))_{t\geq 0}$ be a multivariate L\'evy process with L\'evy measure $\nu(dy) = \exp(-f(|y|)) dy$ for a smoothly regularly varying function $f$ of index $\alpha>1$. The process $L$ is renormalized as $X^\varepsilon(t) = \varepsilon L(r_\varepsilon t)$, $t\in [0, T]$, for a scaling parameter $r_\varepsilon= o(\varepsilon^{-1})$, as $\varepsilon \to 0$. We study the behavior of the bridge $Y^{\varepsilon, x}$ of the renormalized process $X^\varepsilon$ conditioned on the event $X^\varepsilon(T) = x$ for a given end point $x\neq 0$ and end time $T>0$ in the regime of small $\varepsilon$. Our main result is a sample path large deviations principle (LDP) for $Y^{\varepsilon, x}$ with a specific speed function $S(\varepsilon)$ and an entropy-type rate function $I_{x}$ on the Skorokhod space in the limit $\varepsilon \rightarrow 0+$. We show that the asymptotic energy minimizing path of $Y^{\varepsilon, x}$ is the linear parametrization of the straight line between $0$ and $x$, while all paths leaving this set are exponentially negligible. We also infer a LDP for the asymptotic number of jumps and establish asymptotic normality of the jump increments of $Y^{\varepsilon, x}$. Since on these short time scales $r_\varepsilon = o(\varepsilon^{-1})$) direct LDP methods cannot be adapted we use an alternative direct approach based on convolution density estimates of the marginals $X^{\varepsilon}(t)$, $t\in [0, T]$,for which we solve a specific nonlinear functional equation.