Testing Inflation with Large Scale Structure: Connecting Hopes with Reality

Abstract

The statistics of primordial curvature fluctuations are our window into the period of inflation, where these fluctuations were generated. To date, the cosmic microwave background has been the dominant source of information about these perturbations. Large scale structure is however from where drastic improvements should originate. In this paper, we explain the theoretical motivations for pursuing such measurements and the challenges that lie ahead. In particular, we discuss and identify theoretical targets regarding the measurement of primordial non-Gaussianity. We argue that when quantified in terms of the local (equilateral) template amplitude f loc NL (f eq NL ), natural target levels of sensitivity are ∆f loc,eq. NL 1. We highlight that such levels are within reach of future surveys by measuring 2-, 3-and 4-point statistics of the galaxy spatial distribution. This paper summarizes a workshop held at CITA (University of Toronto) on October 23-24, 2014 [Link]. BNL-1124147-2014-IR Contents 4 Beyond the Halo Power Spectrum 4.1 State of Bispectrum Observations 4.

Non-Gaussianity as a particle detector

“…Even optimistic projections for future CMB observations won't reduce the constraints by more than an order of magnitude. Digging deeper will require new cosmological probes, such as observations of the large-scale structure (LSS) of the universe [62] and the tomography of the 21 cm transition of neutral hydrogen gas [63]. Our results, together with [6,7,[9][10][11], will help to find optimal observational strategies for extracting the subtle imprints of extra particles during the inflationary era.…”

Non-Gaussian enhancements of galactic halo correlations in quasi-single field inflation

“…Even larger scales will be probed in upcoming large scale surveys such as SPHEREx. Prospects for future improvements in measurements of the galactic power spectrum and bispectrum are reviewed in [30].…”

Large non-gaussianity in slow-roll inflation

“…It is clear from eq. (1.2) that having f NL ∼ > 1 in this model implies going beyond the (at least apparent) regime of validity of the low-energy effective theory, which requires (∂φ) 2 Λ 4 . Therefore, unless the infinite number of derivative operators in the ellipses of eq.…”

“…It is a common feature of these models that the magnitude of non-Gaussianity is suppressed [1] well below the observable level for any foreseeable future; see, e.g., [2].…”