Using Large Scale Structure to test Multifield Inflation

Abstract

Primordial non-Gaussianity of local type is known to produce a scale-dependent contribution to the galaxy bias. Several classes of multi-field inflationary models predict non-Gaussian bias which is stochastic, in the sense that dark matter and halos don't trace each other perfectly on large scales. In this work, we forecast the ability of next-generation Large Scale Structure surveys to constrain common types of primordial non-Gaussianity like $f_{NL}$, $g_{NL}$ and ${\tau }_{NL}$ using halo bias, including stochastic contributions. We provide fitting functions for statistical errors on these parameters which can be used for rapid forecasting or survey optimization. A next-generation survey with volume $V=25h^{-3}$Gpc${}^3$, median redshift $z=0.7$ and mean bias $b_g=2.5$, can achieve $\sigma (f_{NL})=6$, $\sigma (g_{NL})=10^5$ and $\sigma ({\tau }_{NL})=10^3$ if no mass information is available. If halo masses are available, we show that optimally weighting the halo field in order to reduce sample variance can achieve $\sigma (f_{NL})=1.5$, $\sigma (g_{NL})=10^4$ and $\sigma ({\tau }_{NL})=100$ if halos with mass down to $M_{min}=10^{11}$ $h^{-1}{M}_{\odot }$ are resolved, outperforming Planck by a factor of 4 on $f_{NL}$ and nearly an order of magnitude on $g_{NL}$ and ${\tau }_{NL}$. Finally, we study the effect of photometric redshift errors and discuss degeneracies between different non-Gaussian parameters, as well as the impact of marginalizing Gaussian bias and shot noise.

17 pages, 6 figures. Comments are welcome. Typo fixed

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Cited by in corpus (2)

• Shot noise and biased tracers: a new look at the halo model
• Single-Field Inflation and the Local Ansatz: Distinguishability and Consistency