Loosely Bound Composite Dark Matter

TL;DR

This paper explores loosely bound composite dark matter states, revealing their potential for large scattering cross sections and unique detection signatures due to their atomic-scale interactions.

Contribution

It introduces models of nuclear and molecular dark matter with large cross sections and novel detection signatures, expanding the understanding of composite dark matter.

Findings

Loosely bound composites can have cross sections scaling as A^4.

They produce extremely soft individual recoils but large total energy depositions.

Potential for new detection signatures in low threshold experiments.

Abstract

We investigate loosely bound composite states made of dark matter, where the binding energy for constituent particles is less than the constituent mass. We focus on models of nuclear and molecular dark matter, where constituents are separated by length scales larger than the inverse constituent mass, just like nuclei and atoms in the Standard Model. The cosmology, structure, and interactions at underground experiments are described. We find that loosely bound composites can have a very large cross section for scattering with nuclei that scales with nucleon number like $\sim A^4$. For some couplings, these composites produce extremely soft ($\ll$ keV) individual atomic recoils while depositing a large amount of total recoil energy ($\gg$ keV) in a single passage through a detector, implying an interesting new class of signatures for low threshold direct detection.