Observations have shown weak interaction between dark matter clouds in collisions of galaxy clusters. Dark matter may undergo a ``dark electromagnetic'' interaction, behaving like a non-relativistic collisionless plasma of self-interacting dark matter particles. Under this hypothesis, dark matter could exhibit plasma-like instabilities with observational consequences. We investigate this interaction by simulating the collision between two e-e+ plasma slabs that mimics this "dark-electromagnetic" interaction. We use a particle-in-cell code and explore the instabilities driven by the interpenetration of two e-e+ plasma clouds. We show that in both hot and cold regimes, the clouds exhibit significant slowdown after passing through each other unless there is an extremely weak interaction. A significant slowdown due to the Weibel instability invariably slows down the clouds, yielding an extraordinary new constraint on the interaction strength compared to constraints based on collisions.
We are looking for dark matter experts to better identify the relevant consequences for the dark matter community, and help us divulge the results to the right community.
