Solving Unbounded Quadratic BSDEs by a Domination Method
Résumé
We introduce a domination argument which asserts that: if we can dominate the
parameters of a quadratic backward stochastic differential equation (QBSDE) with continuous
generator from above and from below by those of two BSDEs having ordered solutions, then
also the original QBSDE admits at least one solution. This result is presented in a general
framework: we do not impose any integrability condition on none of the terminal data of the
three involved BSDEs, we do not require any constraint on the growth nor continuity of the
two dominating generators. As a consequence, we establish the existence of a maximal and
a minimal solution to BSDEs whose coefficient H is continuous and satisfies |H(t, y, z)| ≤
α t + β t |y| + θ t |z| + f (|y|)|z| 2 , where α t , β t , θ t are positive processes and the function f is
positive, continuous and increasing (or even only positive and locally bounded) on R. This is
done with unbounded terminal value. We cover the classical QBSDEs where the function f is
constant ([10], [12], [23], [25]) and when f (y) = y p ([21]) and also the cases where the generator
has super linear growth such as y|z|, e |y| |z| p , e e |z| 2 , (k ≥ 0, 0 ≤ p < 2) and so on. In
contrast to the works [10, 12, 21, 23, 25], we get the existence of a a maximal and a minimal
solution and we cover the BSDEs with at most linear growth (take f = 0). In particular,
we cover and extend the results of [22] and [24]. Furthermore, we establish the existence and
uniqueness of solutions to BSDEs driven by f (y)|z| 2 when f is merely locally integrable on R.
Mots clés
Superlinear backward stochastic differential equations
Quadratic backward stochas-tic differential equations
unbounded solutions maximal and a minimal
AMS 2000 Classification subjects: 60H10
60H20
60H30
91G10 Keywords : Superlinear backward stochastic differential equations
Quadratic backward stochastic differential equations
Domaines
Probabilités [math.PR]Origine | Fichiers produits par l'(les) auteur(s) |
---|
Loading...