Papers › Primordial non-Gaussianity without tails -- how to measure fNL with the bulk of the density PDF
Primordial non-Gaussianity without tails -- how to measure fNL with the bulk of the density PDF
Oliver Friedrich, Cora Uhlemann, Francisco Villaescusa-Navarro, Tobias Baldauf, Marc Manera, Takahiro Nishimichi
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We investigate the possibility to detect primordial non-Gaussianity by analysing the bulk of the probability distribution function (PDF) of late-time cosmic density fluctuations. For this purpose we devise a new method to predict the impact of general non-Gaussian initial conditions on the late-time density PDF. At redshift z=1 and for a smoothing scale of 30Mpc/h our predictions agree with the high-resolution Quijote N-body simulations to ∼0.2% precision. This is within cosmic variance of a ∼100(Gpc/h)³ survey volume. When restricting to this 30Mpc/h smoothing scale and to mildly non-linear densities (δ[30Mpc/h] ∈[-0.3, 0.4]) and also marginalizing over potential ignorance of the amplitude of the non-linear power spectrum an analysis of the PDF for such a survey volume can still measure the amplitude of different primordial bispectrum shapes to an accuracy of \smash{Δf_(NL)ˡᵒᶜ=±7.4 , Δf_(NL)^(equi)=±22.0 , Δf_(NL)ᵒʳᵗʰᵒ=±46.0} . When pushing to smaller scales and assuming a joint analysis of the PDF with smoothing radii of 30Mpc/h and 15Mpc/h (δ[15Mpc/h] ∈[-0.4, 0.5]) this improves to \smash{Δf_(NL)ˡᵒᶜ=±3.3 , Δf_(NL)^(equi)=±11.0 , Δf_(NL)ᵒʳᵗʰᵒ=±17.0} - even when marginalizing over the non-linear variances at both scales as two free parameters. Especially, such an analysis could simultaneously measure f_(NL) and the amplitude and slope of the non-linear power spectrum. However, at 15Mpc/h our predictions are only accurate to ≲0.8% for the considered density range. We discuss how this has to be improved in order to push to these small scales and make full use of upcoming surveys with a PDF-based analysis.
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