Malliavin calculus and decoupling inequalities in Banach spaces

We develop a theory of Malliavin calculus for Banach space-valued random variables. Using radonifying operators instead of symmetric tensor products we extend the Wiener–Itô isometry to Banach spaces. In the white noise case we obtain two sided L p -estimates for multiple stochastic integrals in arbitrary Banach spaces. It is shown that the Malliavin derivative is bounded on vector-valued Wiener–Itô chaoses. Our main tools are decoupling inequalities for vector-valued random variables. In the opposite direction we use Meyerʹs inequalities to give a new proof of a decoupling result for Gaussian chaoses in UMD Banach spaces.