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Enhancement of DM relic density from the late time DM conversions

Enhancement of DM relic density from the late time DM conversions. Ze-Peng Liu, Yue-Liang Wu, and Yu-Feng Zhou (arXiv: 1101.4148). 2-component case. The effective cross section A interesting limit Approximate form. Themal evolution. Thermal equilibrium with SM

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Enhancement of DM relic density from the late time DM conversions

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  1. Enhancement of DM relic density from the late time DM conversions • Ze-Peng Liu, Yue-Liang Wu, and Yu-Feng Zhou • (arXiv: 1101.4148)

  2. 2-component case • The effective cross section • A interesting limit • Approximate form

  3. Themal evolution • Thermal equilibrium with SM • Decouple from SM, but still in equilibrium with each other • Late time DM conversion at large z • Slow conversion characterized by r(z) • Crossing point • Complete decouple (freeze-out) after Freeze-out condition Y1(z) increased eventually

  4. Numerical Result • Equilibrium • Equilibrium density Y2

  5. Numerical Result • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1

  6. Numerical Result • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1 • If no conversion • Decoupling of Y2 • Decoupling of Y1

  7. Numerical Result • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1 • If no conversion • Decoupling of Y2 • Decoupling of Y1 • With conversion • Evolution of Y2 • Evolution of Y1

  8. Numerical Result • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1 • If no conversion • Decoupling of Y2 • Decoupling of Y1 • With conversion • Evolution of Y2 • Evolution of Y1 • Evolution of Y1+Y2

  9. Conditions for a large boost factor • Large internal degree of freedom of Y2: • Small mass difference: • Cross sections satisfy: • Approximate expression for the boost factor

  10. boost factor (B) B vs relative cross sections B vs mass difference

  11. A simple 2CDM Model • Add to the SM

  12. A simple 2CDM Model • Add to the SM mediators

  13. A simple 2CDM Model Cross sections Other processes are suppressed by p-wave. Enhanced by the resonance

  14. Summary • In multi-DM models, DM conversion can significantly modify the thermal evolution of each DM component. • The relic density of the DM component may not always inversely proportional to it’s annihilation cross section. Through conversions from heavier DM components, the relic density of light DM can be enhanced, leading to large boost factors. • The boost factor is independent of DM relative velocity. For generic models with large conversion rate the boost fact can reach the value required by PAMELA etc.

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