UMICH-2015: Inflation Summary

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Inflation summary

what would detection of r mean?

  • What if we detect r > 0.001?:
    • Does it tell us the energy scale of inflation? Conclusion (from Scott Watson): yes due to unseen NG
    • Sets bounds on graviton mass
    • We know inflation traversed super-Planckian field space distance (large field) which implies some symmetry to protect against corrections
  • What if we find r < 0.001?:
    • Exclude Starobinsky/Higgs inflation and monomial -- only models where ns -1 ~ 1/N (not as an accident)

Natural targets / thresholds?

  • r: 0.01 (monomial) and 0.003 (Starobinsky) are both natural targets motivating sensitivity threshold of sigma(r) = 0.001. Such sensitivity would disfavor two large classes of inflationary models, or detect a new signal. Note that assumed value would affect strategy.
  • ns: ns not equal to 1 is only natural target of which we are aware. This has already been passed, but we can reduce model dependence. This is a parameter that is difficult to improve dramatically beyond current uncertainties.
  • Consistency condition: Single-field slow roll with canonical kinetic term leads to nt = -r/8. Almost certainly too small to be seen by CMB-S4. Post-BICEP2 r=0.2 paper by Scott Dodelson provides relevant forecasts. Yes, we need to think big. Is this too big?
  • nt: nt > -2 is a target. And we can get at nt > 0.2 due to contribution to Neff.
  • running: Both monomial and Starobinsky lead to running too small to see. For CMB-S4 expect roughly sigma(alpha) = 0.002. Hard to improve on with LSS. Want polarization out to high ell.
  • Features: Generically expect features from some interesting models, but they could easily be undetectably small. No natural thresholds.
  • Three-point function in scalars: Can get fNL of order unity from multi-field models and single-field models w/ non-trivial dynamics. There may be some interesting targets here from factor of ~few reduction in error beyond what Planck has done, since "order unity" might mean as big as five for some models. LSS expected to do better. Combination of CMB-S4 and LSS may probe scale dependence of fNL. No natural target known of here.
  • Four-point function: tauNL ~ fNL squared is natural target: out of reach
  • Non-Gaussianity in tensors?: no known natural targets. Obviously highly dependent on r.
  • Isocurvature: No known threshold
  • Topological defects: ? Interaction with isocurvature?
  • Primordial magnetic fields: may drive requirements on polarization angle calibration (because makes EB not 0)

Anomalies: leading hyp

Bottom line for survey/ experiment design: r drives design one direction, Mnu and Neff another. All inflation stuff besides r drives things in similar ways as Neff and Mnu, not r. The exception is anomalies. Large-angle polarization may provide key clues for understanding large-scale temperature anomalies.

Delensing and Foregrounds:

  • Blake: need high sensitivity lensing map.Plot shows residual delensed B-mode noise on large scales vs. noise of the high-res lens-reconstruction-experiment (right figure from Smith et al. 2010).