Rethinking Inflation and the Search for Alternatives

2. Rethinking Inflation and the Search for Alternatives

3. Inflation Great explanatory power: horizon – flatness – monopoles – entropy Great predictive power: Wtotal = 1 nearly scale-invariant perturbations slightly red tilt adiabatic gaussian gravitational waves consistency relations - ? ? ?

4. “the classic(al) perspective” dominantly a classical process… an ordering process… in which quantum physics plays a small but important perturbative role

5. “the (true) quantum perspective” Inflation is dominantly a quantum process… in which (classical) inflation amplifies rare quantum fluctuations… resulting in a peculiar kind of disorder

6. Eternal Inflation Vilenkin, 1983 PJS, 1983

7. “I would argue that once one accepts eternal inflation as a logical possibility, then there is no contest in comparing an eternally inflating version of inflation with any theory that is not eternal....” Alan Guth, 2000

8. Powerfully predictive? Linde, Linde, Mezhlumian, PRD 50, 2456 (1994)

9. If Eternal to the Past, then maybe we can uniquely determine the probabilities. SINGULARITY PROBLEM cf. Borde and Vilenkin, PRL 72, 3305 (1994); PRD 56, 717 (1997)

10. Maybe can find measure that does • not depend on initial conditions Global vs. Local Measures?

11. Immune from initial conditions?

12. Important properties insensitive to initial conditions? Garriga, Guth and Vilenkin, hep-th/0612242 Aguirre, Johnson and Shomer, arxiv:0704.3473 Chang, Kleban, Levi, arxiv:07012.2261 Aguirre, Johnson, arxiv:0712.3038 “Persistence of Memory Effect” tinitial

13. Important properties insensitive to initial conditions? t = 0 YELLOW: anisotropic!

14. Perhaps we know the Iniitial Condiions?? • Entropy Problem: • requires entropically disfavored initial state? Penrose

15. “the (true) quantum perspective” • Singularity problem • Unpredictability problem • Persistence of memory • Entropy problem theory incomplete ? threatens flatness and scale invariance? threatens isotropy? advantage  problem

16. Search for Alternatives

17. “the (true) quantum perspective” • Singularity problem • Unpredictability problem • Persistence of memory • Entropy problem 1) Inflation is fast energy density large or Hsmoothing > Hnormal >> Htoday 2) Quantum physics is random

18. “the (true) quantum perspective” • Singularity problem • Unpredictability problem • Persistence of memory • Entropy problem But suppose Hsmoothing << Hnormal

19. How do we go from small H to large H ? Hsmoothing contracting implies must resolve singularity problem

20. Cyclic model Ekpyrotic model “ekpyrotic contraction” “ekpyrotic contraction” bounce bounce radiation radiation . . . matter dark energy

21. w >> 1 ekpyrotic phase: ultra-slow contraction with w >>1 Erickson, Wesley, PJS. Turok Erickson, Gratton, PJS, Turok w N.B. Do not need finely tuned initial conditions or inflation or dark energy …

22. w >> 1 ekpyrotic phase: ultra-slow contraction with w >>1 Erickson, Wesley, PJS. Turok Erickson, Gratton, PJS, Turok w … and avoid chaotic mixmaster behavior …

23. w >> 1 ekpyrotic phase: ultra-slow contraction with w >>1 Erickson, Wesley, PJS. Turok Erickson, Gratton, PJS, Turok w … and Hsmoothing << Hnormal and contracting

24. w >> 1 ekpyrotic phase: ultra-slow contraction with w >>1 Erickson, Wesley, PJS. Turok Erickson, Gratton, PJS, Turok w … and scale-invariant perturbations of scalar fields.

25. How to get w >> 1 ? “branes” Field-theory V f f

26. A Role for Observations Curiously, precisiontests can distinguish the two key qualitative differences between inflation and ekpyrotic/cyclic models • Hsmoothing is exponentially different • w is orders of magnitude different gravitational waves local non-gaussianity

27. 3 z = zL + fNLzL2 5 “local” non-gaussianity generated when modes are outside the horizon (“local” NG) Maldacena Komatsu & Spergel “intrinsic” NG contribution (positive fNL) depending on e = (1 + w) or steepness of potential 3 2