Primordial physics from largescale structure beyond the power spectrum
Abstract
We study constraints on primordial modecoupling from the power spectrum, squeezedlimit bispectrum and collapsed trispectrum of matter and halos. We describe these statistics in terms of longwavelength $2$point functions involving the matter/halo density and positiondependent power spectrum. This allows us to derive simple, analytic expression for the information content, treating constraints from scaledependent bias in the halo power spectrum on the same footing as those from higher order statistics. In particular, we include nonGaussian covariance due to longshort modecoupling from nonlinear evolution, which manifests itself as longmode cosmic variance in the positiondependent power spectrum. We find that bispectrum forecasts that ignore this cosmic variance may underestimate $\sigma(f_{\rm NL})$ by up to a factor $\sim 3$ for the matter density (at $z=1$) and commonly a factor $\sim 2$ for the halo bispectrum. Constraints from the bispectrum can be improved by combining it with the power spectrum and trispectrum. The reason is that, in the positiondependent power spectrum picture, the bispectrum and trispectrum intrinsically incorporate multitracer cosmic variance cancellation, which is optimized in a joint analysis. For halo statistics, we discuss the roles of scaledependent bias, matter modecoupling, and nonlinear, nonGaussian biasing ($b_{11}^{(h)}$). While scaledependent bias in the halo power spectrum is already very constraining, higher order halo statistics are competitive in the regime where stochastic noise in the positiondependent halo power spectrum is low enough for cosmic variance cancellation to be effective, i.e.~for large halo number density and large $k_{\rm max}$. This motivates exploring this regime observationally.
 Publication:

arXiv eprints
 Pub Date:
 February 2018
 DOI:
 10.48550/arXiv.1802.06762
 arXiv:
 arXiv:1802.06762
 Bibcode:
 2018arXiv180206762D
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 48 pages, 20 figures. Comments welcome