  The interactions between a relativistic magnetized collisionless shock and
dense clumps have been expected to play a crucial role on the magnetic field
amplification and cosmic-ray acceleration. We investigate this process by
two-dimensional Particle-In-Cell (PIC) simulations for the first time, where
the clump size is much larger than the gyroradius of downstream particles. We
also perform relativistic magnetohydrodynamic (MHD) simulations for the same
condition to see the kinetic effects. We find that particles escape from the
shocked clump along magnetic field lines in the PIC simulations, so that the
vorticity is lower than that in the MHD simulations. Moreover, in both the PIC
and MHD simulations, the shocked clump quickly decelerates because of
relativistic effects. Owing to the escape and the deceleration, the shocked
clump cannot amplify the downstream magnetic field in relativistic
collisionless shocks. This large-scale PIC simulation opens a new window to
understand large-scale behaviors in collisionless plasma systems.
