Primordial Non-Gaussianity in the Forest: 3D Bispectrum of Ly-alpha Flux Spectra Along Multiple Lines of Sight

TL;DR

This paper explores how the 3D bispectrum of Ly-alpha forest spectra can be used to constrain primordial non-Gaussianity, providing predictions for bounds on the parameter fnl with various survey configurations.

Contribution

It presents the first predictions for constraining fnl using Ly-alpha flux spectra along multiple lines of sight, modeling the flux as a biased tracer of matter.

Findings

In an ideal survey, fnl can be constrained to about 23.

Large sky surveys could constrain fnl to around 100.

Potential for joint inflationary scenario constraints with other data sets.

Abstract

We investigate the possibility of constraining primordial non-Gaussianity using the 3D bispectrum of Ly-alpha forest. The strength of the quadratic non-Gaussian correction to an otherwise Gaussian primordial gravitational field is assumed to be dictated by a single parameter fnl. We present the first prediction for bounds on fnl using Ly-alpha flux spectra along multiple lines of sight. The 3D Ly-$\alpha$ transmitted flux field is modeled as a biased tracer of the underlying matter distribution sampled along 1D skewers corresponding to quasars sight lines. The precision to which fnl can be constrained depends on the survey volume, pixel noise and aliasing noise (arising from discrete sampling of the density field). We consider various combinations of these factors to predict bounds on fnl. We find that in an idealized situation of full sky survey and negligible Poisson noise one may constrain fnl ~ 23 in the equilateral limit. Assuming a Ly-alpha survey covering large parts of the sky (k_{min} = 8 * 10^{-4} Mpc^{-1}) and with a quasar density of \bar n = 5 * 10^{-3} Mpc^{-2} it is possible to constrain fnl ~ 100 for equilateral configurations. The possibility of measuring fnl at a precision comparable to LSS studies maybe useful for joint constraining of inflationary scenarios using different data sets.