A Dark-Disk Universe

TL;DR

This paper proposes a new form of dark matter called Double-Disk Dark Matter (DDDM) that could form a disk within galaxies, interact strongly enough to cool and settle into a rotational disk, and produce detectable signals.

Contribution

It introduces the concept of DDDM, a subcomponent of dark matter capable of dissipative interactions leading to disk formation, expanding the scope of dark matter models.

Findings

DDDM could make up a significant fraction of dark matter.

DDDM's gravitational effects could be observable in stellar motions.

Annihilation of DDDM might produce distinctive gamma-ray signals.

Abstract

We point out that current constraints on dark matter imply only that the majority of dark matter is cold and collisionless. A subdominant fraction of dark matter could have much stronger interactions. In particular, it could interact in a manner that dissipates energy, thereby cooling into a rotationally-supported disk, much as baryons do. We call this proposed new dark matter component Double-Disk Dark Matter (DDDM). We argue that DDDM could constitute a fraction of all matter roughly as large as the fraction in baryons, and that it could be detected through its gravitational effects on the motion of stars in galaxies, for example. Furthermore, if DDDM can annihilate to gamma rays, it would give rise to an indirect detection signal distributed across the sky that differs dramatically from that predicted for ordinary dark matter. DDDM and more general partially interacting dark matter scenarios provide a large unexplored space of testable new physics ideas.