Dark Matter on a Slide

TL;DR

This paper proposes a GeV-scale thermal dark matter model involving dark pions and mesons, with unique collider signatures from long-lived dark particles decaying visibly, testable mainly at the LHC.

Contribution

It introduces a minimal dark sector model with dark pions and mesons, stabilized by a U(1) symmetry, and explores collider signals from dark showers with long-lived particles.

Findings

Correct relic density achieved with specific dark meson mass splittings.

Dark matter detection via direct and indirect searches is ineffective due to symmetry.

LHC signatures include dark showers with long-lived dark η decays to visible states.

Abstract

We present a scenario for GeV-scale thermal dark matter that can only be tested with accelerator experiments. Dark matter is composed of dark pions arising from a confining strong interaction in the dark sector. The thermal relic density is obtained through the interplay of up-scatterings of dark pions to heavier dark mesons (the dark counterparts of the kaons and $\eta$), and decays of the unstable dark $\eta$ to Standard Model particles. This mechanism is analogous to a playground slide, where one climbs up first and then slides down with a release of energy. We illustrate the scenario with a minimal model based on the SU(3)/SO(3) coset, where dark matter is stabilized by a U(1) flavor symmetry. The correct relic density is obtained with dark meson mass splittings of 10% to 50% and a dark-$\eta$ lifetime shorter than $10^3\,\mathrm{m}/c$. Direct and indirect dark matter searches are mostly ineffective, as a consequence of the charge conjugation symmetry of the stabilizing U(1). The most striking signals arise at the LHC, from the production of dark showers containing long-lived dark $\eta$'s that decay to visible final states. These signatures crucially depend on the portal interaction connecting the dark sector to the Standard Model. We show that several well-known portals can complete the scenario above the weak scale, and outline the expected signals in each case.