[Paper Review] A Scenario of Heavy Baryonic Dark Matter

Ran Huo, Shigeki Matsumoto+2 more|arXiv (Cornell University)|Jun 23, 2015

Dark Matter and Cosmic Phenomena20 references3 citations

TL;DR

This paper proposes a composite dark matter model where dark matter consists of baryons and antibaryons from a hidden SU(3) vector-like strong gauge theory. The model naturally explains the observed dark matter relic abundance via unitarity-saturated annihilation and ensures long-term stability via an accidental dark baryon number symmetry, with a predicted lifetime near current observational bounds that can reconcile with AMS-02 antiproton data.

ABSTRACT

We consider a general class of models in which dark matter is a composite baryonic and antibaryonic particle of some hidden vector-like strong gauge theory. The model building provides simple answers to two basic questions: Annihilation between dark baryon and antibaryon saturates the unitarity bound, which in thermal freeze out predicts the scale of dark matter particle to be about 150 TeV. And the dark matter stability is a result of the accidental dark baryon number, which can still be violated by operators suppressed by large scales, leading to tiny decay rate. We show that annihilation between dark baryon and anti-baryon seems difficult to be detected in the galaxy center in the near future. On the other hand in the minimal model of $SU(3)$ hidden strong gauge group with a Planck scale suppression, the dark matter life time happens to be marginal to the current detection bound, and can explain the current AMS-02 antiproton results.

Motivation & Objective

• To construct a dark matter model where the relic abundance is naturally explained by unitarity-saturated annihilation of dark baryons and antibaryons.
• To ensure dark matter stability through an accidental dark baryon number symmetry, with possible decay via high-scale suppressed operators.
• To assess the detectability of dark matter annihilation in the galactic center, particularly via indirect detection.
• To explore whether the model can explain the AMS-02 antiproton excess without violating cosmological or astrophysical constraints.

Proposed method

• Construct a hidden strong gauge theory with SU(3) gauge group and vector-like quarks to form composite dark baryons and antibaryons.
• Use thermal freeze-out calculations with unitarity-bounded annihilation cross sections to derive the dark matter mass scale (~150 TeV).
• Identify the accidental dark baryon number symmetry as the protection mechanism for dark matter stability.
• Evaluate the suppression scale of dimension-6 operators that violate dark baryon number, estimating the resulting decay rate.
• Compute the expected antiproton flux from dark matter decay and compare it with AMS-02 data.
• Assess the detectability of dark matter annihilation signals in the galactic center, considering current and near-future sensitivity limits.

Experimental results

Research questions

• RQ1 What is the natural dark matter mass scale that arises from unitarity-saturated annihilation in a composite dark matter model?
• RQ2 How does an accidental dark baryon number symmetry ensure long-lived dark matter while allowing for suppressed decay?
• RQ3 Can the model explain the observed excess of antiprotons measured by AMS-02?
• RQ4 Why is direct detection of dark matter annihilation in the galactic center unlikely in the near future?
• RQ5 What is the role of the Planck-scale suppression in determining the dark matter lifetime and its compatibility with observations?

Key findings

• The dark matter mass is predicted to be approximately 150 TeV, consistent with thermal freeze-out under unitarity-saturated annihilation.
• The accidental dark baryon number symmetry protects dark matter from rapid decay, while higher-dimensional operators allow for a tiny but non-zero decay rate.
• The model's predicted antiproton flux from dark matter decay is consistent with the current AMS-02 data, particularly when the suppression scale is at the Planck scale.
• The lifetime of dark matter in the minimal SU(3) model is marginally above the current observational lower bound, making it a viable candidate.
• Annihilation signals in the galactic center are unlikely to be detected in the near future due to insufficient cross-section and astrophysical background limitations.