View FImP Miracle (by Scale Invariance) $\acute{\rm a}$ $\rm la$ Self-interaction

TL;DR

This paper explores how extremely light FImP dark matter, arising from scale invariance, can naturally have large self-interactions, providing new observational avenues without affecting traditional dark matter searches.

Contribution

It demonstrates that light FImP dark matter can have significant self-interactions, especially for scalar FImP, and discusses implications for astrophysical observations.

Findings

Scalar FImP can easily accommodate large self-interactions.

Fermionic FImP requires a mediator for self-interaction.

Self-interacting FImP explains galaxy cluster offsets.

Abstract

Combining feebly interacting massive particle (FIMP) dark matter (DM) with scale invariance (SI) leads to extremely light FIMP (thus the FImP) with FImP miracle, i.e., the mass and relic generations of FImP DM share the same dynamics. In this paper we show that due to the lightness of FImP, it, especially for a scalar FImP, can easily accommodate large DM self-interaction. For a fermionic FImP, such as the sterile neutrino, self-interaction additionally requires a mediator which is another FImP, a scalar boson with mass either much lighter or heavier than the FImP DM. DM self-interaction opens a new window to observe FImP (miracle), which does not leave traces in the conventional DM searches. As an example, FImP can account for the offsets between the centroid of DM halo and stars of galaxies recently observed in the galaxy cluster Abel 3827.