Paper detail

Constraints from CMB lensing tomography with projected bispectra

We measure the angular power spectrum and bispectrum of the projected overdensity of photometric DESI luminous red galaxies, and its cross-correlation with maps of the Cosmic Microwave Background lensing convergence from \planck. This analysis is enabled by the use of the ``filtered-squared bispectrum'' approach, introduced in previous work, which we generalise here to the case of cross-correlations between multiple fields. The projected galaxy bispectrum is detected at very high significance (above $30σ$ in all redshift bins), and the galaxy-galaxy-convergence bispectrum is detected above $5σ$ in the three highest-redshift bins. We find that the bispectrum is reasonably well described over a broad range of scales by a tree-level prediction using the linear galaxy bias measured from the power spectrum. We carry out the first cosmological analysis combining projected power spectra and bispectra under a relatively simple model, and show that the galaxy bispectrum can be used in combination with the power spectrum to place a constraint on the amplitude of matter fluctuations, $σ_8$, an on the non-relativistic matter fraction $Ω_m$. We find that data combinations involving the galaxy bispectrum recover constraints on these parameters that are in good agreement with those found from the traditional ``2$\times$2-point'' combination of galaxy-galaxy and galaxy-convergence power spectra, across all redshift bins.