Baudoin, Fabrice et Teichmann, Josef, Hypoellipticity in infinite dimensions and an application in interest rate theory, Annals of applied probability , 15(3), 2005, pp. 1765-1777
We apply methods from Malliavin calculus to prove an infinite-dimensional version of Hörmander.s theorem for stochastic evolution equations in the spirit of Da Prato.Zabczyk. This result is used to show that HJM-equations from interest rate theory, which satisfy the Hörmander condition, have the conceptually undesirable feature that any selection of yields admits a density as multi-dimensional random variable.