Effects of QCD bound states on dark matter relic abundance

TL;DR

This paper investigates how QCD bound states influence dark matter relic abundance calculations, revealing that including bound-state effects can significantly increase the predicted maximum dark matter mass compatible with observations.

Contribution

It introduces detailed calculations of bound-state formation and dissociation rates, demonstrating their impact on dark matter relic abundance beyond Sommerfeld enhancement alone.

Findings

Bound-state effects can increase maximum DM mass by 30-100%.

Bino DM mass can reach ~2.5 TeV in specific coannihilation scenarios.

Implications for BBN constraints and collider bounds are discussed.

Abstract

We study scenarios where there exists an exotic massive particle charged under QCD in the early Universe. We calculate the formation and dissociation rates of bound states formed by pairs of these particles, and apply the results in dark matter (DM) coannihilation scenarios, including also the Sommerfeld effect. We find that on top of the Sommerfeld enhancement, bound-state effects can further significantly increase the largest possible DM masses which can give the observed DM relic abundance, by $\sim 30 - 100\%$ with respect to values obtained by considering the Sommerfeld effect only, for the color triplet or octet exotic particles we consider. In particular, it indicates that the Bino DM mass in the right-handed stop-Bino coannihilation scenario in the Minimal Supersymmetric extension of the Standard Model (MSSM) can reach $\sim 2.5$ TeV, even though the potential between the stop and antistop prior to forming a bound state is repulsive. We also apply the bound-state effects in the calculations of relic abundance of long-lived or metastable massive colored particles, and discuss the implications on the BBN constraints and the abundance of a super-weakly interacting DM. The corrections for the bound-state effect when the exotic massive colored particles also carry electric charges, and the collider bounds are also discussed.