1. Direct Search and LHC Detection of the Simplest Dark Matter
Xiao-Gang He
NTU&SJTU
The Simplest Dark Matter Model
Direct Search
Implications for Higgs search at LHC
Discussions and Conclusions

2. Rotation velocity v->Sqrt[1/r] away from optical disc if there is nothing between. But observation show differently.

3. Gravitational lensing

4. Non-Interacting Dark Matter?

6. 1. The Simplest Dark Matter Model
The simplest dark model is the darkon model: SM + real singlet D. Renormalizable interaction only with SM Higgs H With a Z2 symmetry, D -> - D. If not broken, D can play the role of stable dark matter.

7. D is stable, but can annihilate through h exchange

8. Relic density is given by

9. 2. Direct Search

11. 3. Implications for Higgs Search at LHC If Higgs mass is larger than 2 darkon mass, h can decay into darkon h -> DD, increasing invisible width.

12. What if LHC will find a Higgs with small invisible width and dark matter is light?
SM + D, the simplest Darkon model is in trouble. Way out? Yes, Two doublet model + D. There are two CP even Higgs bosons, h and H. h plays the role of the usual Higgs. H a new with different couplings to fermions and gauge bosons and also D. M_h < M_H, LHC finds h, H too heavy for LHC. H plays the role to mediate darkon pair annihilation and produce the relic density. (Yi Cai, X.-G. He, Bo Ren, in preparation)

13. Set lh=0, h decouple from light higgs boson and does not play substantial role for dark matter physics, but H will do.

14. 4. Discussions and Conclusions
If darkon has mass smaller than (m_B-m_K)/2, then B ->K DD possible t -> c DD too small a branching ratio (< 10^{-13}) for detection.

15. The simplest model for dark matter is the darkon model: SM + a real singlet D
It can provide the relic density in a large parameter space.
Direct search rule out some portion of parameter space, but still a large room left for future studies.
If darkon has a mass less than 2 time of Higgs mass, h -> DD increases the invisible width, affecting the way to detect Higgs boson at the LHC.
If darkon has a mass less than (m_B-m_K)/2, B -> K DD can occur.

16. Effects of 4th generation
If D heavier than 4th generation fermions, new channel open for annihilation. Modify relic density. New heavy quark change h -> gg, Modify rare decays B -> K DD, (factor of a few) t -> c D D, increase to 10^{-8} New t’(b’) -> t (b) DD

17. Relic density with 3 and 4 generations

18. Direct search with 3 and 4 generations

19. Invisible h -> DD with 3 and 4 generations