Abstract

Backward stochastic differential equations extend the martingale representation theorem to the nonlinear setting. This can be seen as path-dependent counterpart of the extension from the heat equation to fully nonlinear parabolic equations in the Markov setting. This paper extends such a nonlinear representation to the context where the random variable of interest is measurable with respect to the information at a finite stopping time. We provide a complete wellposedness theory which covers the semilinear case (backward SDE), the semilinear case with obstacle (reflected backward SDE), and the fully nonlinear case (second order backward SDE).

Highlights

  • Let (Ω, F, {Ft}t≥0, P) be a filtered probability space, supporting a d-dimensional Brownian motion W

  • Second order backward SDE with random terminal time reduces to the case ξ = g(Wt0, . . . , Wtn ) for an arbitrary partition 0 = t0 < . . . < tn = T of

  • In view of the formulation of second order backward SDEs as backward SDEs holding simultaneously under a non-dominated family of singular measures, we review –and complement– the corresponding theory of backward SDEs, and we develop the theory of reflected backward SDEs, which is missing in the literature, and which plays a crucial role in the wellposedness of second order backward SDEs

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Summary

Introduction

Let (Ω, F , {Ft}t≥0, P) be a filtered probability space, supporting a d-dimensional Brownian motion W. Our main interest in this paper is on the extension to the fully nonlinear second order parabolic equations, as initiated in the finite horizon setting by Soner, Touzi & Zhang [40], and further developed by Possamaï, Tan & Zhou [34], see the first attempt by Cheridito, Soner, Touzi & Victoir [9], and the closely connected BSDEs in a nonlinear expectation framework of Hu, Ji, Peng & Song [17, 18] (called GBSDEs) This extension is performed on the canonical space of continuous paths with canonical process denoted by X.

Canonical space
Random horizon backward SDE
Random horizon reflected backward SDE
Random horizon second order backward SDE
E P0 τ eρtft0 2dt q 2
Wellposedness of random horizon reflected BSDEs
A priori estimates
We first prove that
Stability of reflected backward SDEs
It remains to verify the announced estimate on t 0
Wellposedness of reflected backward SDEs
Special case: backward SDE
Second order backward SDE: representation and uniqueness
Second order backward SDE: existence
Backward SDEs on the shifted spaces
Measurability – random horizon
Dynamic programming principle
Connection to a fully nonlinear elliptic path-dependent PDE
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