Density jump as a function of the field for parallel relativistic collisionless shocks

Density jump as a function of the field for parallel relativistic collisionless shocks
Antoine Bret, Ramesh Narayan
arXiv:2506.07973v1 Announce Type: cross
Abstract: Collisionless shocks are frequently analyzed using the magnetohydrodynamic formalism (MHD), even though the required collisionality hypothesis is not fulfilled. In a previous work citep{BretJPP2018}, we presented a model of collisionless shock displaying an important departure from the expected MHD behavior, in the case of a strong flow aligned magnetic field. This model was non-relativistic. Here, it is extended to the relativistic regime, considering zero upstream pressure and upstream Lorentz factor $gg 1$. The result agrees satisfactorily with Particle-in-Cell simulations and shows a similar, and important, departure from the MHD prediction. In the strong field regime, the density jump $r$, seen in the downstream frame, behaves like $r sim 2 + 1/gamma_{mathrm{up}}$ while MHD predicts 4 ($gamma_{mathrm{up}}$ is the Lorentz factor of the upstream measured in the downstream frame). Only pair plasmas are considered.arXiv:2506.07973v1 Announce Type: cross
Abstract: Collisionless shocks are frequently analyzed using the magnetohydrodynamic formalism (MHD), even though the required collisionality hypothesis is not fulfilled. In a previous work citep{BretJPP2018}, we presented a model of collisionless shock displaying an important departure from the expected MHD behavior, in the case of a strong flow aligned magnetic field. This model was non-relativistic. Here, it is extended to the relativistic regime, considering zero upstream pressure and upstream Lorentz factor $gg 1$. The result agrees satisfactorily with Particle-in-Cell simulations and shows a similar, and important, departure from the MHD prediction. In the strong field regime, the density jump $r$, seen in the downstream frame, behaves like $r sim 2 + 1/gamma_{mathrm{up}}$ while MHD predicts 4 ($gamma_{mathrm{up}}$ is the Lorentz factor of the upstream measured in the downstream frame). Only pair plasmas are considered.