Title: Critical line of exponents, scattering theories for a weighted gradient system of semilinear wave equations

Abstract: In this paper, we consider the following Cauchy problem of a weighted gradient system of semilinear wave equations \begin{equation*} \left\{ \begin{array}{lll} u_{tt}-\Delta u=\lambda |u|^{\alpha}|v|^{\beta+2}u,\quad v_{tt}-\Delta v=\mu |u|^{\alpha+2}|v|^{\beta}v,\quad x\in \mathbb{R}^d,\ t\in \mathbb{R},\\ u(x,0)=u_{10}(x),\ u_t(x,0)=u_{20}(x),\quad v(x,0)=v_{10}(x),\ v_t(x,0)=v_{20}(x),\quad x\in \mathbb{R}^d. \end{array}\right. \end{equation*} Here $d\geq 3$, $\lambda, \mu\in \mathbb{R}$, $\alpha, \beta\geq 0$, $(u_{10},u_{20})$ and $(v_{10},v_{20})$ belong to $H^1(\mathbb{R}^d)\oplus L^2(\mathbb{R}^d)$ or $\dot{H}^1(\mathbb{R}^d)\oplus L^2(\mathbb{R}^d)$ or $\dot{H}^{\gamma}(\mathbb{R}^d)\oplus H^{\gamma-1}(\mathbb{R}^d)$ for some $\gamma>1$. Under certain assumptions, we establish the local wellposedness of the $H^1\oplus H^1$-solution, $\dot{H}^1\oplus \dot{H}^1$-solution and $\dot{H}^{\gamma}\oplus \dot{H}^{\gamma}$-solution of the system with different types of initial data.