Global convergence rates in the relaxation limits for the compressible Euler and Euler-Maxwell systems in Sobolev spaces

We study two relaxation problems in the class of partially dissipative hyperbolic systems: the compressible Euler system with damping and the compressible Euler-Maxwell system. In classical Sobolev spaces, we derive a global convergence rate of $\mathcal{O}(\varepsilon)$ between strong solutions of the relaxed Euler system and the porous medium equation in $\mathbb{R}^d$ ($d\geq1$) for \emph{ill-prepared} initial data. In a well-prepared setting, we derive an enhanced convergence rate of order $\mathcal{O}(\varepsilon^2)$ between the solutions of the compressible Euler system and their first-order asymptotic approximation. Regarding the Euler-Maxwell system, we prove the global strong convergence of its solutions to the drift-diffusion model in $\mathbb{R}^3$ with a rate of $\mathcal{O}(\varepsilon)$. These results are achieved by developing an asymptotic expansion approach that, combined with stream function techniques, ensures uniform-in-time error estimates.