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General relativity and the standard model of the photon are parity-even, so a detected preference for one handedness on cosmological scales points to new physics: a pseudoscalar field, a Chern–Simons term, or chiral dynamics during inflation.
For a scalar field the power spectrum and bispectrum are blind to parity, because two- and three-point configurations can always be rotated into their mirror images. The lowest parity-odd scalar statistic is the four-point function [@cahn2021]. Tensors and polarisation offer more direct channels. A rotation of the CMB polarisation plane by an angle $\beta$ converts E-modes into B-modes [@lue1999],
\[C_\ell^{EB,\rm obs} = \tfrac12 \sin(4\beta)\left(C_\ell^{EE} - C_\ell^{BB}\right),\]and chiral gravitational waves source TB and EB correlations at low multipoles.
The atlas below crosses four kinds of work (theory, simulation, method, observation) with the place the signal is generated or observed. Each cell is a section with its own revision date; the change log records every revision and every paper added.