Constraining Primordial Non-Gaussianity with Post-reconstructed Galaxy Bispectrum in Redshift Space

TL;DR

This paper demonstrates that post-reconstruction galaxy bispectra significantly improve constraints on primordial non-Gaussianity by reducing covariance and enhancing signal clarity, enabling more precise inflationary physics tests.

Contribution

It shows that galaxy density field reconstruction reduces bispectrum covariance and enhances PNG constraints, with detailed analysis using simulations and Fisher forecasts.

Findings

Bispectrum covariance approaches Gaussian prediction at k<0.2 h/Mpc after reconstruction.

Reconstruction does not affect leading-order PNG bispectrum signals.

Forecasts indicate improved PNG constraints, with Δf_NL reduced by factors of 1.3 to 3.2.

Abstract

Galaxy bispectrum is a promising probe of inflationary physics in the early universe as a measure of primordial non-Gaussianity (PNG), whereas its signal-to-noise ratio is significantly affected by the mode coupling due to non-linear gravitational growth. In this paper, we examine the standard reconstruction method of linear cosmic mass density fields from non-linear galaxy density fields to de-correlate the covariance in redshift-space galaxy bispectra. In particular, we evaluate the covariance of the bispectrum for massive-galaxy-sized dark matter halos with reconstruction by using 4000 independent $N$-body simulations. Our results show that the bispectrum covariance for the post-reconstructed field approaches the Gaussian prediction at scale of $k<0.2\, h\, {\rm Mpc}^{-1}$. We also verify the leading-order PNG-induced bispectrum is not affected by details of the reconstruction with perturbative theory. We then demonstrate the constraining power of the post-reconstructed bispectrum for PNG at redshift of $\sim0.5$. Further, we perform a Fisher analysis to make a forecast of PNG constraints by galaxy bispectra including anisotropic signals. Assuming a massive galaxy sample in the SDSS Baryon Oscillation Spectroscopic Survey, we find that the post-reconstructed bispectrum can constrain the local-, equilateral- and orthogonal-types of PNG with $\Delta f_{\rm NL} \sim$13, 90 and 42, respectively, improving the constraints with the pre-reconstructed bispectrum by a factor of $1.3-3.2$. In conclusion, the reconstruction plays an essential role in constraining various types of PNG signatures with a level of $\Delta f_{\rm NL}<1$ from the galaxy bispectrum based on upcoming galaxy surveys.