LBNL-2016: Inflation Summary

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Status of Inflation Chapter

To participate in the inflation chapter, please join the email list by following instructions you will receive soon in an email from John Carlstrom to the whole CMB-S4 email list.

Warning: there will be telecons.

  1. Introduction
  2. Implications of a detection of primordial gravitational waves with CMB-S4
    • The energy scale of inflation
    • Planckian field ranges and symmetries
    • Constraints on the graviton mass
    • Following up on a detection
  3. Lessons from upper limits
  4. CMB data products and simulations to achieve goals for PGW
  5. Improved constraints on primordial density perturbations
    • The power spectrum of primordial density perturbations
    • Higher order correlations
    • Isocurvature
  6. Constraints on curvature, cosmic birefringence, cosmic strings, axions,...
    • Spatial curvature
    • Cosmic Birefringence
    • Cosmic Strings
    • Anomalies
  7. Summary

Currently needed

  • Realistic forecasts for:
    • tensor-to-scalar ratio (first version from Victor Buza, Colin Bischoff, John Kovac in the draft)
    • tensor spectral index, running
    • scalar spectral index, running
    • non-Gaussianity, including BBB
  • Section on isocurvature modes
  • Additional discussion on bispectrum
  • Discussion of trispectrum
  • Discussion of bubble collisions
  • Streamline various sections
  • Complete section on anomalies

Open questions

Bigger picture questions

  • Should the inflation chapter be thought of as independent at some level? If so, it should likely include higher level discussion
  • CMB-S4 can only reach theoretically well motivated thresholds for r. As a consequence r is the main inflationary driver of the design, and the chapter is focused on primordial gravitational waves. Other aspects imply CMB-S4 will have high angular resolution. Should the discussion of constraints on the power spectrum, bispectrum,... be expanded?
  • Should the inflation chapter be focused on inflation or include implications of high-scale inflation for other areas of fundamental physics?
  • How to approach the issue of alternatives to inflation? This potentially sheds light on why inflation is given so much attention. What to say about Ekpyrosis, if anything?

More detailed questions

  • How much time and effort should be spent on strawman models that produce B-mode power in excess of the inflationary signal?
  • Should various sections be moved or remain in the inflation chapter?
    • Constraints on the graviton
    • Birefringence


  • If you want to contribute, sign up for the e-mail list. Tell the list what you want to do.
  • Given that much of the path forward is forecast-related, which transcends this chapter, how do we organize?
  • How frequently should the inflation working group be having telecons?
  • What is our next deadline? We should have something earlier than end of the summer. What goals to set for being accomplished on a month time scale? Two-month time scale?

Notes from Plenary Discussion

We began with questions about who the audience is for the Science Book. John C said DOE, NSF, and ourselves.

Lloyd suggested having targets for a shorter time scale than "end of summer" would be helpful. It was suggested that June 15 was a good target for having the inflation chapter essentially completed, with changes expected in the forecasting section as that matures over the summer.

The remainder of these notes were taken by Joel Meyers.

  • Alternatives to inflation
    • should be addressed but how?
    • CMBpol: Appendix showed work was done, but alternatives are not yet predictive

Lyman: Gravitational waves should lead, with inflation as a secondary consideration. Are we looking for GW to prove inflation, ar are we interested in GW themselves?

Raphael: GW are fundamentally new probe of early universe

Lyman, Raphael, Renee: Restructure science book? Possibly chapter on GW.

Dick, Arthur (?): GW and Inflation inherently coupled.

Possible new title: Observables of the early universe

Renee: restructure to separate observables from implications

Raphael: Benefits to repetition

Lloyd: As an orgnaizational point, this restructuring would be difficult right now, requiring coordination among more people. I propose we stick wtih current structure, and restructuring could potentially be done later.

  • How do we organize forecasts?
    • Chapter 6: Forecasting and modeling is in simulations and analysis chapter 6. Should it be promoted to its own chapter?
    • Fisher forecasts independent, but validation is unified
  • Need to set shorter-term goals for science book.
    • John C: Need enough feedback, including forecasts, to create strawman instrumental design by end of summer 2016.
  • Sections should be expanded wherever clarity (Physics-Today-level explanation) can be added. Detailed technical derivations are not as useful.

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