Non-Gaussianity constraints with anisotropic mu distortion measurements from Planck

Primordial non-Gaussianity can source A-distortion anisotropies that are correlated with the large-scale temperature and polarization signals of the cosmic microwave background (CMB). A measurement of mu T and mu E correlations can therefore be used to constrain it on wavelengths of perturbations not directly probed by the standard CMB anisotropies. We carry out a first rigorous search for mu-distortion anisotropies with Planck data, applying the well-tested constrained MC component-separation method combined with the needlet framework. We correlate the reconstructed mu map with the CMB anisotropies to derive constraints on the amplitudefn of the local form bispectrum, specifically on the squeezed configurations with effective wavenumbers k(s) similar or equal to 740 Mpc(-1) and k(L) similar or equal to 0.05 Mpc(-1), improving previously estimated constraints by more than an order of magnitude. This enhancement is owing to the fact that we are able to use the full multipole information by carefully controlling biases and systematic effects in the analysis. We also for the first time incorporate constraints from measurements of mu E correlations, which further tighten the limits. A combination of the derived Planck mu T and mu E power spectra yields vertical bar fNL vertical bar less than or similar to 6800 (95 per cent c.l.) on this highly squeezed bispectrum. This is only similar or equal to 3 times weaker than the anticipated constraint from Litebird. Furthermore we show that a combination of Litebird with Planck can improve the expected future constraint by similar or equal to 20%. These limits can be used to constrain multifield inflation models and primordial black hole formation scenarios, thus providing a promising novel avenue forward in CMB cosmology.