Sub-GeV Dark Matter Shining at Future MeV γ-Ray Telescopes

Area of Science:

• Particle Physics
• Cosmology
• Astrophysics

Background:

• Current dark matter (DM) models face challenges in detection and cosmological consistency.
• Light (sub-GeV) dark matter candidates are particularly difficult to detect with existing experimental sensitivities.
• Cosmic Microwave Background (CMB) data places stringent constraints on early Universe physics, limiting DM properties.

Purpose of the Study:

• To propose a novel framework for detecting light dark matter (DM) with future MeV gamma-ray telescopes.
• To ensure the proposed DM model is consistent with CMB data and other cosmological observations.
• To provide model-independent realizations and explore parameter constraints within this framework.

Main Methods:

• Introducing a stable DM particle (χ) with a high annihilation cross-section, leading to low thermal relic abundance.
• Utilizing a heavier, metastable partner particle (ψ) with suppressed annihilation rates to store DM number density.
• Implementing late-time decays of the partner particle (ψ→χ) to populate the Universe with DM.
• Analyzing constraints from CMB, Big Bang Nucleosynthesis (BBN), and Large Scale Structure (LSS) on the model parameters.

Main Results:

• Demonstrated a viable mechanism for producing light DM without perturbing the CMB.
• Established that the DM relic abundance can be generated through late-time decays of a heavier partner.
• Identified specific model-independent realizations of this framework.
• Derived constraints on the parameters governing the late-time decays from cosmological data.

Conclusions:

• The proposed framework offers a promising avenue for detecting light dark matter with MeV gamma-ray telescopes.
• The model successfully reconciles light DM with stringent CMB constraints.
• Future cosmological observations can further refine the parameter space of this dark matter scenario.