A note on Tricomi-type partial differential equations with white noise initial condition

Abstract: We study a class of Tricomi-type partial differential equations previously investigated in [28]. Firstly, we generalize the representation formula for the solution obtained there by allowing the coefficient in front of the second-order partial derivative with respect to $x$ to be any non integer power of $t$. Then, we analyze the robustness of that solution by taking the initial data to be Gaussian white noise and we discover that the existence of a well-defined random field solution is lost upon the introduction of lower-order terms in the operator. This phenomenon shows that, even though the Tricomi-type operators with or without lower-order terms are the same from the point of view of the theory of hyperbolic operators with double characteristics, their corresponding random versions exhibit different well posedness properties. We also prove that for more regular initial data, specifically fractional Gaussian white noise with Hurst parameter $H\in (1/2,1)$, the well posedness of the Cauchy problem for the Tricomi-type operator with lower-order term is restored.