In this thesis, we study the decay rates of the highest order (M-th order) spatial derivatives for solutions of both compressible Hall MHD system and that with Coulomb force by a pure energy method inspired by Guo and Wang (2012)[12] and Gao, Li and Yao (2023)[9]. When the norm of H3 for the initial perturbation is small enough, and the norms of both HM(Mâ„3) and HËâα(αâ[0,32)) for that only need to be bounded, we first prove the decay rates of compressible Hall MHD system in L2 are (1+t)â(M+α)2. And then affected by the Coulomb force, for compressible Hall MHD system with Coulomb force, we obtain the decay rates are (1+t)â(M+α)2 for αâ[12,32) and (1+t)12[(14â12α)â(M+α)] for αâ[0,12), which are consistent with the decay estimates for compressible MHD system with Coulomb force. In particular, the results improve the original decay rates (1+t)â(Mâ1+α)2 established by Xu et al. (2016)[46] and Tan, Tong and Wang (2015)[31].
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