B-Modes in CMB Polarization - any change since BICEP2 in 2015?

[Cerenkov]

TL;DR Summary

https://arxiv.org/abs/1502.00612 A Joint Analysis of BICEP2/Keck Array and Planck Data

Hello.

I was wondering if there have been any further developments on the topic of B-modes in the CMB polarization since this 2015 paper?

https://arxiv.org/abs/1502.00612 A Joint Analysis of BICEP2/Keck Array and Planck Data

The above paper declares that... 'We find strong evidence for dust and no statistically significant evidence for tensor modes.'

In the eight years since this paper have there been any noteworthy observations or re-evaluations of the data?

Thank you for any help given,

Cerenkov.

 

[Hyperfine]

To the best of my knowledge, no. The observations are far from trivial. The amplitude of the primordial B-mode polarization is expected to be smaller than that of the foreground resulting from lensing and dust.

 

[Cerenkov]

Thank you Hyperfine.

Your reply prompts further questions.

1.
Will it be feasible for the foreground lensing and dust to be sufficiently well mapped for their effects to be subtracted, thus revealing the B-modes? (Assuming that they exist, of course.)

2.
At the risk of widening the remit of this thread I'm also prompted to ask if there are other potential indicators of inflation, either encoded into the CMB or to be found elsewhere?

3.
On Sunday you responded to this thread... https://www.physicsforums.com/threads/what-does-the-te-cmb-spectrum-reveal.1051316/ ...and mentioned Will Kinney's work on the TE cross-correlation power spectrum, as described in chapter 6 of his book, An Infinity of Worlds : Cosmic Inflation and the Beginning of the Universe. On the back of your input and various reviews I've ordered that book, Hyperfine. Thank you for piquing my interest.

So, for a basic-level member of this forum like me, could you please explain what superhorizon modes are and what the anti-correlation of the low multipole moments are? Thanks again,

Cerenkov.

 

[Hyperfine]

Will it be feasible for the foreground lensing and dust to be sufficiently well mapped for their effects to be subtracted, thus revealing the B-modes? (Assuming that they exist, of course.)

I hope that is possible. It depends on the amplitude of the primordial B-modes.

At the risk of widening the remit of this thread I'm also prompted to ask if there are other potential indicators of inflation, either encoded into the CMB or to be found elsewhere?

Be patient. Wait for your copy of Kinney to arrive and digest slowly.

So, for a basic-level member of this forum like me, could you please explain what superhorizon modes are and what the anti-correlation of the low multipole moments are?

Within the framework of inflation, primordial density perturbations which we ultimately observe as temperature anisotropies in the CMB, result from quantum fluctuations in the so-called inflaton field. Inflation stretches the wavelengths of those quantum fluctuations. Inflation takes place at speeds exceeding $c$ while the cosmic horizon expands at speeds less than $c$. When the wavelength of a quantum mode is stretched such that it is larger than the cosmic horizon, that mode is said to be "superhorizon". The concept is important from a dynamical point of view.

Regarding anti-correlation:

Here anticorrelation means that larger temperature fluctuations are statistically associated with negative polarization on very large angular scales.

Again, the book should help to clarify the matter. My personal interpretation is that the important observation is that there is a peak in the TE cross-correlation power spectrum at angular scales that are larger than the cosmic horizon.

 

[Cerenkov]

Thanks for your help, Hyperfine.

Also, thank for explaining about superhorizons and anti-correlation in terms that I can understand. Yes, I will have to be VERY patient in my wait for Kinney's book. According to the Amazon page that I used, the paperback version won't be available (here in the UK) until... October. So I've pre-ordered.Thanks again,

Cerenkov.

 

[Jaime Rudas]

Regarding the detection of the B-modes of the polarization of the CMB, a few months ago the first module of the QUBIC project began to operate.

 

[Cerenkov]

That's very interesting news Jaime, thank you!

I've just checked out that Wiki page and the QUBIC site itself.

https://www.qubic.org.ar/en/qubic-argentina-english/

Given what Hyperfine has said about foreground lensing and dust, let's hope that the amplitude of the B-mode polarization is within QUBIC's sensitivity.

Fingers crossed!Thanks again,

Cerenkov.