1. Alex Vilenkin (Tufts University) Miami, December 2014 TOPOLOGICAL DEFECTS FROM THE MULTIVERSE

2. False vacuum Bubbles You are here Bubbles nucleate and expand in the course of eternal inflation. The multiverse

3. This would be a direct test of eternal inflation. Bubble collisions can leave an imprint on the CMB. Aguirre, Freivogel, Kleban, Johnson, … How can we test multiverse models ? Indirect tests: Predictions for the cosmological constant, neutrino masses, negative spatial curvature, etc. Weinberg, … Pogosian, Tegmark & A.V. Freivogel, Kleban, Martinez & Susskind

4. Cosmic strings or domain walls nucleating in the parent vacuum may “intrude” in our bubble. Inflating false vacuum Our bubble Cosmic string loop These can be fundamental or field theory strings. They can be very heavy. This talk: J. Zhang, J. Blanco-Pillado, J. Garriga & A.V. (work in progress)

5. Strings and domain walls in dS space Basu, Guth & A.V. (1991) tunnel Tunneling is also possible from r = 0 spontaneous nucleation. S4S4 S2S2 The instanton: String worldsheet – Nucleation rate: Similarly for domain walls: string tension

6. String / wall worldsheet Physical radius: “Nucleation moment”: Nucleation center: Conformal diagram t = t n

7. Scale-invariant size distribution: Time independent: production balances stretching and dilution. Lower cut-off:

8. Scale-invariant size distribution: Time independent: production balances stretching and dilution. Lower cut-off: Strings & walls will collide with expanding bubbles

9. Simple model: dS space inside and outside the bubble with expansion rates H T and H F, respectively. Approximate the bubble wall by a light cone. Disregard gravity of the bubble wall and of the defects. FRW slices

10. Simple model: The string appears to be infinite on FRW slices. (There are also some closed loops.) dS space inside and outside the bubble with expansion rates H T and H F, respectively. String worldsheet can be continued into the bubble.. Approximate the bubble wall by a light cone. Disregard gravity of the bubble wall and of the defects. FRW slices String worldsheet Bubble wall FRW slice

11. Asymptotic shapes of strings are circles on the Poincare disc. We can see only up to. (The curvature radius is.) FRW metric inside the bubble: The string “freezes” at in comoving coordinates.

12. Observational effects A string within our horizon could cause gravitational lensing of the CMB and of distant galaxies. Best fit to the data is for Jazayeri et al. (2014) A domain wall within or close to our observable region could account for the hemispherical power asymmetry. How likely is this?

13. Number of defects within our bubble as a function of distance: Domain walls: Strings: (for ) We are not likely to see defects in our neighborhood. For :

14. Observing collision events Observer Collisions in our past light cone can produce observable effects. The intruding defect can be very far away on the FRW slice when the signal reaches the observer.

15. Observing collision events Expected number of events: Can be large even for. Observer Collisions in our past light cone can produce observable effects. The intruding defect can be very far away on the FRW slice when the signal reaches the observer. Freivogel et al (2009) found a similar enhancement for bubble collisions.

16. Distribution of “collision marks” on the sky Domain walls: disc-like marks. Angular size distribution:

17. “Collision marks” of strings

18. Observable effects may occur within the future light cone of the collision. Collisions with strings can produce gravitational waves – unlike collisions with domain walls or other bubbles.

19. Other types of defects Walls bounded by strings Global monopoles