UMICH-2015: Inflation break-out session 1

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B-modes challenges: foregrounds and de-lensing

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Foregrounds

  • What are our latest estimates of foreground levels post-Planck?
  • What simulations and tools do we have for forecasting impact on r? (details for Tuesday)
  • What are still physical unknowns?
  • Do we need new data at <40 GHz and >230 GHz? (and 60 GHz?)
  • How important is large sky area?
  • What is the path to a convincing claim that a B-mode signal is not foregrounds?

Delensing

  • What is the impact of delensing on r, and on nt or BB wiggles?
  • How does internal CMB delensing compare to external (e.g. CIB)?
  • What sensitivity and resolution do we need for the lensing map?

Foregrounds

What are our latest estimates of foreground levels post-Planck?

Steve, Raphael...

  • Figure from Steve Choi/Lyman Page:

Choi.png

  • John Ruhl: Can we make a new version of this figure (Steve could make input, who made it originally?):

OldFG.png


What simulations and tools do we have for forecasting impact on r? (detailed discussion on Tues)

Jacques, Raphael, Stephen F, Aurelien, Brendan, Jo...

  • Aurelien: Addressing questions about model uncertainty requires a flexible simulation facility, which can be easily modified and run by everyone for a wide range of parameters, and interfaced with current analysis and forecasting pipelines. Ideally would use python and have mechanism for the community to contribute to development and easily make and share own simulations. PSM is great, but how do we make the best use of it as a starting point.
  • Brendan: had a problem using the PSM during the BKP analysis – the dust polarization model in the PSM comes from a filtered version of Planck 353, so includes Planck noise, and there is nowhere in the PSM sky that is as clean as dust as the real Bicep region
  • We still still want ability to do quick and dirty Fisher forecasts for exploring different set-ups, so still want quick ways to inflate Nl for example.



What are still physical unknowns?

Aurelien, Brandon Hensley, Bruce Draine, Al Kogut, Brendan

  • They include magnetic dust, spinning dust polarization, spatial dispersion of dust temperature/emissivity...
  • Brendan: At what point we think that the greybody model for dust emission will break down?
  • Aurelien: worried by the spatial variations of dust properties. Taking these into account in forecasts is difficult, since they represent a failure in our theoretical understanding. How do we get around this? Is there a way to cook up a strategy, in terms of frequency and spatial coverage, that would make our forecasts somewhat immune to these uncertainties?
  • Jo: Don't yet know enough from Planck: dispersion in dust index between individual 300 deg2 (i.e. large!) patches is about +-0.15 and varies between beta = 1.1 and 2.2.
  • Al Kogut has done sims for PIXIE to look at possible residuals given varying dust temperature

Do we need new data at <40 GHz and >230-300 GHz? And what about 60GHz?

Clem,John, Aurelien, Jo...

  • The effective polarized noise from cleaning 150 GHz with Planck 353 GHz is about 19 uK-arcmin, i.e. an additional sigma(r) ~0.01 for fsky=0.2
  • John: useful figure from BKP:

Bkp fig13.png

  • Jo: pessimistic/realistic inflation of CMB errors using map-based cleaning if we loosen dust assumptions:

Index.png

  • Aurelien: For 60 GHz, want something there in the long term to understand dust / synchrotron correlations. But in the medium term, how well can we do without it?

How important is large sky area?

  • Without foregrounds, fsky doesn't help you that much. But! required if you want detections from different regions of sky.

What is the path to a convincing claim that a B-mode signal is not foregrounds?

  • Nulls between frequencies, areas, scales

Delensing

(Blake Sherwin, Olivier Dore, Chris Sheehy, Josquin Errard, Stephen Feeney, Alex van Engelen, Neelima Sehgal, Anthony Challinor...)

What is the impact of delensing on r, and on nt or BB wiggles?


How does internal CMB delensing compare to external (e.g. CIB)?

  • Blake says external cleaning won't be good enough for 1 uK noise levels.

What sensitivity and resolution do we need for the lensing map?

  • Blake: need high sensitivity lensing map