Can we really measure fnl from the galaxy power spectrum?

Abstract

The scale-dependent galaxy bias generated by primordial non-Gaussianity (PNG) can be used to detect and constrain deviations from standard single-field inflation. The strongest signal is expected in the local model for PNG, where the amplitude of non-Gaussianity can be expressed by a set of parameters (fnl, gnl, ...). Current observational constraints from galaxy clustering on fnl and gnl assume that the others PNG parameters are vanishing. Using two sets of cosmological N-body simulations where both fnl and gnl are non-zero, we show that this strong assumption generally leads to biased estimates and spurious redshift dependencies of the parameters. Additionally, if the signs of fnl and gnl are opposite, the amplitude of the scale-dependent bias is reduced, possibly leading to a false null detection. Finally we show that model selection techniques like the Bayesian evidence can (and should) be used to determine if more than one PNG parameter is required by the data.

5 pages, 3 figures. Accepted for publication in MNRAS Letters. Minor changes to previous version

References in corpus (3)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Bayes in the sky: Bayesian inference and model selection in cosmology
• The imprints of primordial non-gaussianities on large-scale structure: scale dependent bias and abundance of virialized objects

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• Constraints on primordial non-Gaussianity from 800,000 photometric quasars
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• Using Large Scale Structure to test Multifield Inflation
• Hunting high and low: Disentangling primordial and late-time non-Gaussianity with cosmic densities in spheres
• Precise Calibration of the One-Loop Bispectrum in the Effective Field Theory of Large Scale Structure
• Non-local bias in the halo bispectrum with primordial non-Gaussianity
• Primordial non-Gaussianity in the bispectra of large-scale structure
• Precise Calibration of the One-Loop Trispectrum in the Effective Field Theory of Large Scale Structure
• General relativistic corrections and non-Gaussianity in large scale structure
• Lifting Primordial Non-Gaussianity Above the Noise
• Testing Multi-Field Inflation with Galaxy Bias