Influence of plasma instabilities on interpenetrating plasma clouds as a test for electromagnetic dark matter self-interactions

Dark matter (DM) could be charged under its own ``dark electromagnetism'' (DEM), behaving like a cold collisionless plasma of self-interacting DM~particles. Under this hypothesis, DM could exhibit plasma-like instabilities [1] with observational consequences. We investigate this via PIC simulations [2], exploring the instabilities driven by the interpenetration of two e-e$+$ plasma clouds that mimic the ``dark plasma.'' We show that the clouds slow down mostly due to~Weibel generated magnetic fields, which deflect the particle trajectories, such that particles acquire transverse momentum, thus leading to an isotropic velocity~distribution. This process causes the flow velocity to decrease approximately by 1/2 in a time interval $\Delta $t~$=$ 1/$\surd \alpha \Delta $v(c/v), where $\alpha $ is the equipartition parameter, v~the initial flow speed and c the light speed, comparable with the plasma instability growth time. We show that if the typical DM slab length is much longer than v$\Delta $t, DM particles are always expected to slow~down by a factor of about 1/2. Comparison with astronomical observations may yield new constraints on DEM. \\[4pt] [1] L. Ackerman et al~~Phys.Rev. D79 023519 (2009)(2006).\\[0pt] [2] R. A. Fonseca et al., LNCS 2331, 342 (2002).