How to Build an Alternative to Inflation

1. How to Build an Alternative to Inflation 朴 云 松 中国科学院研究生院

2. The idea behind inflation should be more interesting than inflation self, which may bring us more thoughts are there alternatives to inflation ?

3. Problems of Big Bang cosmology • Why inflation is successful ? • How to build an alternative • Summary

4. i.

5. ii.

6. iii.

7. inflation a period of accelerated expansion of early universe

10. if it is actually inflation, the amusements left are play models and fit observations

11. the game is actually ... however, it may be not inflation ?

12. There can be a scenario ? it can solve same problems (or some of problems) with those solved by inflation generate scale invariant primordial perturbation

13. it requires a|H| increases with time

15. Thus if there can be a solution to the problem of standard cosmology

17. contraction expansion

18. what is the efolding number ? for perturbation, not for scale factor

19. inflation inflation slow expansion slow contraction

20. slow contraction slow expansion

21. contraction expansion what can lead the scale invariant scalar spectrum ?

22. and are same only in

23. The reason is is the increasing mode when

26. for

28. constant mode increasing mode cyclic universe Piao (03) island universe (05,07)

29. island universe

31. The cyclic and island a is nearly unchanged. H is rapidly increased. The inflation a is rapidly increased. H is nearly unchanged. This duality is a natural result of duality between their background evolutions.

32. how to distinguish inflation ( ) and scenarios with i.non-Gaussianity In general, non-Gaussianity for inflation, it is small, however, it can be large by other methods. for , it is natural large for example, if ,

33. cyclic universe (Steinhardt et.al.) island universe

34. ii. Tensor spectrum Steinhardt et.al.

35. For there are lots of studies. However, the problems It is not an attractor solution. It leads to

36. Thus contraction expansion ？ There are only a little points responsible for scale invariance. However, the perturbation is induced by background field. This is natural.

37. some “unnatural” mechanisms i. non background field recall “curvaton” in inflation game Thus the perturbation can be induced by also light field. it initially is used in PBB picture. contraction expansion PBB

38. In principle, the scale invariance can be obtained for any . however, it requires a special behavior of field. In general, a. non minimal coupled kinetic term b. change of mass with time

39. contraction expansion ？ background field non background field

40. some “unnatural” mechanisms ii. change speed of sound it might be scale Invariant for any and any evolutions however, some problems of standard cosmology will remain. expansion contraction ?

41. Summary the idea behind inflation is more interesting than inflation self. inflation is consistent, however, there are alternatives. may be tested by coming observations.

42. Have all possibilities been explored ? …… Thank You