## The Annals of Probability

### Nonuniqueness for a parabolic SPDE with $\frac{3}{4}-\varepsilon$-Hölder diffusion coefficients

#### Abstract

Motivated by Girsanov’s nonuniqueness examples for SDEs, we prove nonuniqueness for the parabolic stochastic partial differential equation (SPDE) $\frac{\partial u}{\partial t}=\frac{\Delta}{2}u(t,x)+\bigl|u(t,x)\bigr|^{\gamma}\dot{W}(t,x),\qquad u(0,x)=0.$ Here $\dot{W}$ is a space–time white noise on $\mathbb{R}_{+}\times\mathbb{R}$. More precisely, we show the above stochastic PDE has a nonzero solution for $0<\gamma<3/4$. Since $u(t,x)=0$ solves the equation, it follows that solutions are neither unique in law nor pathwise unique. An analogue of Yamada–Watanabe’s famous theorem for SDEs was recently shown in Mytnik and Perkins [Probab. Theory Related Fields 149 (2011) 1–96] for SPDE’s by establishing pathwise uniqueness of solutions to $\frac{\partial u}{\partial t}=\frac{\Delta}{2}u(t,x)+\sigma \bigl(u(t,x)\bigr)\dot{W}(t,x)$ if $\sigma$ is Hölder continuous of index $\gamma>3/4$. Hence our examples show this result is essentially sharp. The situation for the above class of parabolic SPDE’s is therefore similar to their finite dimensional counterparts, but with the index $3/4$ in place of $1/2$. The case $\gamma=1/2$ of the first equation above is particularly interesting as it arises as the scaling limit of the signed mass for a system of annihilating critical branching random walks.

#### Article information

Source
Ann. Probab., Volume 42, Number 5 (2014), 2032-2112.

Dates
First available in Project Euclid: 29 August 2014

https://projecteuclid.org/euclid.aop/1409319473

Digital Object Identifier
doi:10.1214/13-AOP870

Mathematical Reviews number (MathSciNet)
MR3262498

Zentralblatt MATH identifier
1301.60080

#### Citation

Mueller, Carl; Mytnik, Leonid; Perkins, Edwin. Nonuniqueness for a parabolic SPDE with $\frac{3}{4}-\varepsilon$-Hölder diffusion coefficients. Ann. Probab. 42 (2014), no. 5, 2032--2112. doi:10.1214/13-AOP870. https://projecteuclid.org/euclid.aop/1409319473