The Power of Locality: Primordial Non-Gaussianity at the Map Level. (arXiv:2112.14645v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Baumann_D/0/1/0/all/0/1">Daniel Baumann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Green_D/0/1/0/all/0/1">Daniel Green</a>
Primordial non-Gaussianity is a sensitive probe of the inflationary era, with
a number of important theoretical targets living an order of magnitude beyond
the reach of current CMB constraints. Maps of the large-scale structure of the
universe, in principle, have the raw statistical power to reach these targets,
but the complications of nonlinear evolution are thought to present serious, if
not insurmountable, obstacles to reaching these goals. In this paper, we will
argue that the challenge presented by nonlinear structure formation has been
overstated. The information encoded in primordial non-Gaussianity resides in
nonlocal correlations of the density field at three or more points separated by
cosmological distances. In contrast, nonlinear evolution only alters the
density field locally and cannot create or destroy these long-range
correlations. This locality property of the late-time non-Gaussianity is
obscured in Fourier space and in the standard bispectrum searches for
primordial non-Gaussianity. We therefore propose to measure non-Gaussianity in
the position space maps of the large-scale structure. As a proof of concept, we
study the case of equilateral non-Gaussianity, for which the degeneracy with
late-time nonlinearities is the most severe. We show that a map-level analysis
is capable of breaking this degeneracy and thereby significantly improve the
constraining power over previous estimates. Our findings suggest that
“simulation-based inference” involving the forward modeling of large-scale
structure maps has the potential to dramatically impact the search for
primordial non-Gaussianity.
Primordial non-Gaussianity is a sensitive probe of the inflationary era, with
a number of important theoretical targets living an order of magnitude beyond
the reach of current CMB constraints. Maps of the large-scale structure of the
universe, in principle, have the raw statistical power to reach these targets,
but the complications of nonlinear evolution are thought to present serious, if
not insurmountable, obstacles to reaching these goals. In this paper, we will
argue that the challenge presented by nonlinear structure formation has been
overstated. The information encoded in primordial non-Gaussianity resides in
nonlocal correlations of the density field at three or more points separated by
cosmological distances. In contrast, nonlinear evolution only alters the
density field locally and cannot create or destroy these long-range
correlations. This locality property of the late-time non-Gaussianity is
obscured in Fourier space and in the standard bispectrum searches for
primordial non-Gaussianity. We therefore propose to measure non-Gaussianity in
the position space maps of the large-scale structure. As a proof of concept, we
study the case of equilateral non-Gaussianity, for which the degeneracy with
late-time nonlinearities is the most severe. We show that a map-level analysis
is capable of breaking this degeneracy and thereby significantly improve the
constraining power over previous estimates. Our findings suggest that
“simulation-based inference” involving the forward modeling of large-scale
structure maps has the potential to dramatically impact the search for
primordial non-Gaussianity.
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