A weak lensing view on primordial non-Gaussianities

TL;DR

This paper analyzes how weak lensing bispectrum measurements, especially from Euclid, can detect primordial non-Gaussianities, assess model misestimations, and improve understanding of early universe conditions.

Contribution

It provides a detailed forecast of the Euclid survey's sensitivity to different types of primordial non-Gaussianities and introduces efficient Monte Carlo methods for analysis.

Findings

Euclid can constrain fNL to errors of 200, 575, and 1628 for local, orthogonal, and equilateral types.

Misestimations of fNL can be up to a factor of ±3 if wrong models are used.

Weak lensing offers complementary constraints to CMB on primordial non-Gaussianities.

Abstract

We investigate the signature of primordial non-Gaussianities in the weak lensing bispectrum, in particular the signals generated by local, orthogonal and equilateral non-Gaussianities. The questions we address include the signal-to-noise ratio generated in the Euclid weak lensing survey (we find the 1sigma-errors for fNL are 200, 575 and 1628 for local, orthogonal and equilateral non-Gaussianities, respectively), misestimations of fNL if one chooses the wrong non-Gaussianity model (misestimations by up to a factor of +/-3 in fNL are possible, depending on the choice of the model), the probability of noticing such a mistake (improbably large values for the chi^2-functional occur from fNL 200 on), degeneracies of the primordial bispectrum with other cosmological parameters (only the matter density Omega_m plays a significant role), and the subtraction of the much larger, structure-formation generated bispectrum. If a prior on a standard wCDM-parameter set is available from Euclid and Planck, the structure formation bispectrum can be predicted accurately enough for subtraction, and any residual structure formation bispectrum would influence the estimation of fNL to a minor degree. Configuration-space integrations which appear in the evaluation of chi^2-functionals and related quantities can be carried out very efficiently with Monte-Carlo techniques, which reduce the complexity by a factor of O(10^4) while delivering sub-percent accuracies. Weak lensing probes smaller scales than the CMB and hence provide an additional constraint on non-Gaussianities, even though they are not as sensitive to primordial non-Gaussianities as the CMB.