Pathwise uniqueness in infinite dimension under weak structure conditions

Let $U,H$ be two separable Hilbert spaces and $T>0$. We consider an SDE which evolves in the Hilbert space $H$ of the form \begin{align} dX(t)=AX(t)dt+\widetilde{\mathscr L}B(X(t))dt+GdW(t), \quad t\in[0,T], \quad X(0)=x \in H, \end{align} where $A:D(A)\subseteq H\to H$ is the infinitesimal generator of a strongly continuous semigroup $(e^{tA}{)}_{t\ge 0}$, $W=(W(t){)}_{t\ge 0}$ is a $U$-cylindrical Wiener process defined on a normal filtered probability space $(\mathrm{\Omega },\mathcal{F},\{{\mathcal{F}}_t{\}}_{t\in [0,T]},\mathbb{P})$, $B:H\to H$ is a bounded and $\theta$-Hölder continuous function, for some suitable $\theta \in (0,1)$, and $\tilde{\mathcal{L}}:H\to H$ and $G:U\to H$ are linear bounded operators. We prove that, under suitable assumptions on the coefficients, the weak mild solution to the equation depends on the initial datum in a Lipschitz way. This implies that pathwise uniqueness holds true. Here, the presence of the operator $\mathrm{\Lambda }$ plays a crucial role. In particular the conditions assumed on the coefficients cover the stochastic damped wave equation in dimension $1$ and the stochastic damped Euler–Bernoulli Beam equation upto dimension $3$ even in the hyperbolic case.