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Extrema counts of 3D density fields as a new test of primordial non-Gaussianity

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One of the main targets in cosmology is the understanding of the primordial Universe and the mechanism that seeded the cosmic structures we observe today. Despite the great achievements of observing adiabatic, nearly scale-invariant and very close to Gaussian perturbations as predicted by the simplest models of inflation, we are still blind to the particle content of inflation and the precise mechanism of production of primordial perturbations. Observing primordial non-Gaussianity is the best way to discriminate among models of inflation. Well-defined targets for the amplitude of primordial non-Gaussianity are provided by theoretical arguments: for instance, an order one PNG for squeezed triangles would rule out single-field models of inflation. Upcoming galaxy surveys in the next 5-10 years might have the sensitivity to reach this target. Here we propose a new method to observe PNG : a simple proof-of-principle analysis of the extrema (minima and maxima) abundance of the smoothed dark matter and halo density fields in n-body simulations revealed that they are very sensitive to the presence to local-type PNG , as expected from theoretical arguments. The strength of this method resides in the fact that the analysis is very simple to perform, i.e. counting extrema in a smoothed density field, as compared to the usual method of computing correlations of number counts. Despite not providing the required O(1) sensitivity on fNL for this preliminary analysis, we show how this method can be improved in several directions and also extended to other cosmological parameters, such as for example the abundance of dark matter in the Universe.

This talk is part of the Cosmology Lunch series.

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