Quirky Composite Dark Matter

TL;DR

This work introduces quirky dark matter (QDM), a composite dark matter candidate formed from a new non-Abelian force that confines below the electroweak scale. It develops a concrete model with two chiral quirks under SU(2)_Q, mass generation through the Higgs, and a preserved quirky baryon number, then analyzes the bound-state spectrum using non-relativistic methods to show a neutral ground state can arise when quirk masses are nearly degenerate. The cosmological abundance is tied to electroweak sphalerons and depends on anomaly-free invariants and mass-temperature ratios, allowing the observed dark matter density to be matched; direct-detection signals occur mainly via Higgs exchange and higher-dimension operators, with additional gamma-ray line signals from quirky transitions in clusters offering a distinctive astrophysical probe. The framework links electroweak-scale dynamics to dark matter phenomenology, proposing novel experimental channels—direct detection via Higgs and polarizability effects, collider signatures from mesons, and gamma-ray spectroscopy—that can test the model.

Abstract

We propose a new dark matter candidate, quirky dark matter, that is a scalar baryonic bound state of a new non-Abelian force that becomes strong below the electroweak scale. The bound state is made of chiral quirks: new fermions that transform under both the new strong force as well as in a chiral representation of the electroweak group, acquiring mass from the Higgs mechanism. Electric charge neutrality of the lightest baryon requires approximately degenerate quirk masses which also causes the charge radius of the bound state to be negligible. The abundance is determined by an asymmetry that is linked to the baryon and lepton numbers of the universe through electroweak sphalerons. Dark matter elastic scattering with nuclei proceeds through Higgs exchange as well as an electromagnetic polarizability operator which is just now being tested in direct detection experiments. A novel method to search for quirky dark matter is to look for a gamma-ray dark line spectroscopic feature in galaxy clusters that result from the quirky Lyman-alpha or quirky hyperfine transitions. Colliders are expected to dominantly produce quirky mesons, not quirky baryons, consequently large missing energy is not the primary collider signal of the physics associated with quirky dark matter.

Figures (2)

• Figure 1: Sketch of the quantum mechanical energy spectrum of our quirky dark matter composite with the ground state and several excited states shown. Our notation $B^q_S$ corresponds to baryonic states with total electric charge $q$ and total spin $S$. We have included $\mathcal{O}(\bar{\alpha}^2)$ (quirky Lyman-alpha) and $\mathcal{O}(\bar{\alpha}^4)$ (quirky hyperfine) splittings, but do not show the $\mathcal{O}(\bar{\alpha}^5)$ (quirky Lamb shift) splittings or other higher-order effects. The lightest electrically charged baryons $B^\pm_1$ (not shown), have spin one, and are slightly heavier than $B^0_1$ due to subdominant electromagnetic corrections to the potential.
• Figure 2: Contour plots of the density ratio $\rho_D/\rho_B = (1,5,25)$ shown by dashed, solid, dot-dashed (red, blue, green) lines. The axes are the invariants $(I_1,I_2) \equiv (B-L,B-3 D)$ in arbitrary units; a mirror symmetric plot can be obtained taking $(I_1,I_2) \rightarrow (-I_1,-I_2)$. Plot on the left has $M = 200$ GeV, $x = 0.25$, and on the right $M = 1000$ GeV, $x = 0.25$. The plots demonstrate that a viable region exists with $\rho_D/\rho_B \simeq 5$, corresponding to a "bathtub ring" around a valley in $(I_1,I_2)$ space. The bottom of the valley has $\rho_D/\rho_B \simeq 0$.