Ze-Peng Liu, Yue-Liang Wu and Yu-Feng Zhou Kavli Institute for Theoretical Physics China,

1. Enhancement of dark matter relic density from the late time dark matter conversions Ze-Peng Liu, Yue-Liang Wu and Yu-Feng Zhou Kavli Institute for Theoretical Physics China, Institute of Theoretical Physics, Chinese Academy of Sciences arXiv:1101.4148[hep-ph] 海峡两岸粒子与宇宙学研讨会2011.04.01-06, 新竹

2. Outline • Introduction: • evidences of DM from observations • DM candidates: WIMPs • recent experimental results • Thermal evolution of interacting multi-DM • Generic case with multiple component DM models • Boost factor in two-component DM model • Numerical results and a simple model • Conclusions

3. DM revealed from gravitational effects Gravitational curves Large scale structure Bullet clusters Strong lensing CMB Weak lensing

4. What we know about DM • Massive: from gravitational interactions. • Stable: lifetime longer than the age of the Universe • Electro-magnetic and color neutral: dark, but can annihilate into photons • Non-baryonic • MACHOs: disfavored by micro-lensing survey • MOND: disfavored by bullet clusters • D/H from BBN: • CMB: • Non-relativistic motion ( from N-body simulations ) • Cold DM：substructure, halo core • Warm DM ? A big challenge to the standard model of particle physics !

5. DM stability Stability:symmetry + kinematics • Symmetries important for keeping particle stable electron: U(1) em. symmetry, lightest charged particle proton: U(1) B-L symmetry, lightest baryon neutrino: Lorentz symmetry,lightest fermion • DM protected by symmetries Known examples SUSY: R-parity, LSP UED: KK-parity, LKP Little Higgs: T-parity LR model: P and CP parity W.L. Guo, L.M.Wang, Y.L. Wu, YFZ, C. Zhuang Phys.Rev.D79:055015,2009 W.L.Guo, Y.L. Wu, YFZ, Phys.Rev.D82:095004,2010 W.L.Guo, Y.L. Wu, YFZ, Phys.Rev.D81:075014,2010

6. DM relic density: The WIMPs miracle • Thermal freeze out: the origin of species Weakly Interacting Massive Particles (WIMPs) • Particle physics independently predicts WIMPs • WIMPs have just the right relic density • WIMPs are testable by the current exp.

7. Search for non-gravitational effects ? balloon Cherenkov telescope Satellite underground collider

8. Hint of DM ? Positron fraction PAMELA if interpreted as DM signal • Large annihilation cross section now, boost factor problem. • Sommerfeld enhancement ? • Resonance enhancement ? • Non-thermal DM ? • DM may slightly decay ? • Mainly annihilation/decay into leptons, not quarks • Light final states <1GeV ? • Leptophilic interaction ? background Nature 458, 607 (2009)

9. Hint of DM? electrons plus positrons ATIC/PPB-BETS • Excess in the total flux • peak at ~600 GeV • rapid drop below 800GeV Fermi LAT • Spectrum harder than expected background with power index around ~3. Nature, 456, 2008,362-365 Phys.Rev.Lett.102:181101,2009

10. Direct searches

11. CRESST

12. EDELWEISS-II EDELWEISS-II, arXiv:1103.4070.

13. The std. WIMP annihilation cross section is too small to account for the PAMELA/Fermi data Positron flux Boost factor Need a large boost factor B~100-1000 The boost factor problem Bergstrom, Edsjo, Zaharijas, PRL103,031103,09’

14. Possible origins of boost factor Boot factor for DM annihilation • Local clumps Via Lactea II: in subhalo? B~ 4-15, • Temperature-dependent ann. cross section • Sommerfeld enhancement • Resonance enhancement Diemand, et al, 0805.1244, Nature Sommerfeld, Ann. Phy 403, 257 (1931). J. Hisano, S. Matsumoto and M. M. Nojiri, Phys. Rev. D 67 (2003) Phys. Rev. Lett. 92, 031303 (2004) Feldman, Liu, Nath, 09 Ibe, Murayama, Yanagida, 09 Guo, Wu, 09 Other mechanism: DM decay, non-thermal DM ….

15. Constraints from relic density J. L. Feng, M. Kaplinghat and H. B. Yu, Phys. Rev. Lett. 104, 151301 (2010) arXiv:1005.4678 • Refined analysis at freeze-out • Cut-off of resonance, recoupling • Force-carrier production & • decay rates • Kinetic decoupling • Self-interaction efficiency, • non-thermality • Other constraints • Halo shape • CMB, protohalo J. Zavala, M. Vogelsberger and S. D. M. White, Phys. Rev. D 81, 083502 (2010) M. Kamionkowski and S. Profumo, Phys. Rev. Lett. 101,261301 (2008)

16. Large boost requires Large annihilation cross section Still the correct relic density Impossible for one-component thermal DM? Multi-component DM Models with hidden sectors naturally have multi-DM DM may have SUSY partners Neutrinos are already (tiny) part of DM boost from simply mixed thermal multi-DM ? (No) Boost factor from interacting multi-DM ?(Possible) Boost factor in multi-component DM models For thermal relic large cross section Always reduces signal Z.P.Liu, Y.L.Wu and YFZ, arXiv:1101.4148

17. Thermal evolution of interacting multi-DM The components can be converted • Thermal evolution for interacting DM • Use common variable

18. the DM conversion process • Maintain thermal equilibrium between the DM components, after decoupling from the SM thermal bath • Convert the heavy DM into the light

19. Thermal evolution of the total density • The total density at equilibrium • The total density evolves like an ordinary WIMP at early time effective cross section is temperature-dependent

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

21. Thermal evolution for two-component DM • 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

22. Numerical results • Equilibrium • Equilibrium density Y2

23. Numerical results • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1

24. Numerical results • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1 • If no conversion • Decoupling of Y2

25. Numerical results • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1 • If no conversion • Decoupling of Y2 • Decoupling of Y1

26. Numerical results • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1 • If no conversion • Decoupling of Y2 • Decoupling of Y1 • With conversion • Evolution of Y2

27. Numerical results • Equilibrium • Equilibrium density Y2 • Equilibrium density Y1 • If no conversion • Decoupling of Y2 • Decoupling of Y1 • With conversion • Evolution of Y2 • Evolution of Y1

28. Numerical results • 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

29. Numerical results B vs mass difference B vs relative cross sections

30. 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

31. A simple 2dm model Add to the SM

32. Cross sections

33. 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 velocity. For generic models with large conversion rate the boost fact can reach ~100-1000. Thank You !

34. Thanks !