BICEP2 / <i>Keck Array</i> IX: New bounds on anisotropies of CMB polarization rotation and implications for axionlike particles and primordial magnetic fields
Bibliographic record
Abstract
We present the strongest constraints to date on anisotropies of cosmic microwave background (CMB) polarization rotation derived from 150 GHz data taken by the BICEP2 Keck Array CMB experiments up to and including the 2014 observing season (BK14). The definition of the polarization angle in BK14 maps has gone through self-calibration in which the overall angle is adjusted to minimize the observed $TB$ and $EB$ power spectra. After this procedure, the $QU$ maps lose sensitivity to a uniform polarization rotation but are still sensitive to anisotropies of polarization rotation. This analysis places constraints on the anisotropies of polarization rotation, which could be generated by CMB photons interacting with axionlike pseudoscalar fields or Faraday rotation induced by primordial magnetic fields. The sensitivity of BK14 maps ($\ensuremath{\sim}3\text{ }\text{ }\ensuremath{\mu}\mathrm{K}\text{\ensuremath{-}}\mathrm{arc}\text{ }\mathrm{min}$) makes it possible to reconstruct anisotropies of the polarization rotation angle and measure their angular power spectrum much more precisely than previous attempts. Our data are found to be consistent with no polarization rotation anisotropies, improving the upper bound on the amplitude of the rotation angle spectrum by roughly an order of magnitude compared to the previous best constraints. Our results lead to an order of magnitude better constraint on the coupling constant of the Chern-Simons electromagnetic term ${g}_{a\ensuremath{\gamma}}\ensuremath{\le}7.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}/{H}_{I}$ (95% confidence) than the constraint derived from the $B$-mode spectrum, where ${H}_{I}$ is the inflationary Hubble scale. This constraint leads to a limit on the decay constant of ${10}^{\ensuremath{-}6}\ensuremath{\lesssim}{f}_{a}/{M}_{\mathrm{pl}}$ at mass range of ${10}^{\ensuremath{-}33}\ensuremath{\le}{m}_{a}\ensuremath{\le}{10}^{\ensuremath{-}28}\text{ }\text{ }\mathrm{eV}$ for $r=0.01$, assuming ${g}_{a\ensuremath{\gamma}}\ensuremath{\sim}\ensuremath{\alpha}/(2\ensuremath{\pi}{f}_{a})$ with $\ensuremath{\alpha}$ denoting the fine structure constant. The upper bound on the amplitude of the primordial magnetic fields is 30 nG (95% confidence) from the polarization rotation anisotropies.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".