Primordial non-Gaussianity without tails — how to measure fNL with the bulk of the density PDF. (arXiv:1912.06621v3 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Friedrich_O/0/1/0/all/0/1">Oliver Friedrich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Uhlemann_C/0/1/0/all/0/1">Cora Uhlemann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Villaescusa_Navarro_F/0/1/0/all/0/1">Francisco Villaescusa-Navarro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Baldauf_T/0/1/0/all/0/1">Tobias Baldauf</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Manera_M/0/1/0/all/0/1">Marc Manera</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nishimichi_T/0/1/0/all/0/1">Takahiro Nishimichi</a>
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 $sim 0.2%$
precision. This is within cosmic variance of a $sim 100(mathrm{Gpc}/h)^3$
survey volume. When restricting to this 30Mpc/$h$ smoothing scale and to mildly
non-linear densities ($delta[30mathrm{Mpc}/h] in [-0.3, 0.4]$) 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{$Delta f_{mathrm{NL}}^{mathrm{loc}}=pm 7.4 , Delta
f_{mathrm{NL}}^{mathrm{equi}}=pm 22.0 , Delta
f_{mathrm{NL}}^{mathrm{ortho}}=pm 46.0$} . When pushing to smaller scales
and assuming a joint analysis of the PDF with smoothing radii of 30Mpc/$h$ and
15Mpc/$h$ ($delta[15mathrm{Mpc}/h] in [-0.4, 0.5]$) this improves to
smash{$Delta f_{mathrm{NL}}^{mathrm{loc}}=pm 3.3 , Delta
f_{mathrm{NL}}^{mathrm{equi}}=pm 11.0 , Delta
f_{mathrm{NL}}^{mathrm{ortho}}=pm 17.0 $} – even when marginalizing over
the non-linear variances at both scales as two free parameters. Especially,
such an analysis could simultaneously measure $f_{mathrm{NL}}$ and the
amplitude and slope of the non-linear power spectrum. However, at 15Mpc/$h$ our
predictions are only accurate to $lesssim 0.8%$ 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.
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 $sim 0.2%$
precision. This is within cosmic variance of a $sim 100(mathrm{Gpc}/h)^3$
survey volume. When restricting to this 30Mpc/$h$ smoothing scale and to mildly
non-linear densities ($delta[30mathrm{Mpc}/h] in [-0.3, 0.4]$) 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{$Delta f_{mathrm{NL}}^{mathrm{loc}}=pm 7.4 , Delta
f_{mathrm{NL}}^{mathrm{equi}}=pm 22.0 , Delta
f_{mathrm{NL}}^{mathrm{ortho}}=pm 46.0$} . When pushing to smaller scales
and assuming a joint analysis of the PDF with smoothing radii of 30Mpc/$h$ and
15Mpc/$h$ ($delta[15mathrm{Mpc}/h] in [-0.4, 0.5]$) this improves to
smash{$Delta f_{mathrm{NL}}^{mathrm{loc}}=pm 3.3 , Delta
f_{mathrm{NL}}^{mathrm{equi}}=pm 11.0 , Delta
f_{mathrm{NL}}^{mathrm{ortho}}=pm 17.0 $} – even when marginalizing over
the non-linear variances at both scales as two free parameters. Especially,
such an analysis could simultaneously measure $f_{mathrm{NL}}$ and the
amplitude and slope of the non-linear power spectrum. However, at 15Mpc/$h$ our
predictions are only accurate to $lesssim 0.8%$ 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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