The simplest models of inflation consist of a single, slowly rolling, scalar field. These models seed structure formation with a Gaussian spectrum of primordial density fluctuations. Any deviation from this simple picture, such as: multiple fields, derivative interactions, or features in the inflationary potential can lead to Non-Gaussianity (NG) in the spectrum of initial density perturbations and which manifests itself in cosmological observables. The NG Hub will bring together researchers from around the world to address all aspects of Non-Gaussianity; seeking to identify signatures of NG in current and planned experiments as well guiding the design of future experiments so that they are optimized to detect signatures of NG.

Simulated CMB maps with different levels of non-Gaussianity. The mean temperature in each map is zero, and the parameter fNL controls departures from Gaussianity.
Extracting information on NG out of astronomical observations is a daunting problem. Fortunately, a number of advances have recently been made which point to dramatic opportunities for progress in near future:
  • The formalism to compute NG arising from inflation has evolved significantly.
  • Second-order perturbation theory has been applied to compute the NG coming from gravitational instability and radiative processes; knowledge of the effects of these processes is necessary in order to extract the primordial signal.
  • Algorithms have been developed to extract information about primordial NG from large-scale structure surveys and Cosmic Microwave Background experiments.
  • There is now sufficient computational power and expertise to perform large-scale simulations, which can predict the observable signatures of primordial NG.
  • Large surveys, such as the Dark Energy Survey (DES), are coming online with enough depth and sky coverage to obtain meaningful constraints.

Power spectrum (correlating halos and matter) for different values of the non-Gaussian parameter f_NL. Note that large scales (low wavenumbers k) are particularly sensitive to f_NL. The bias of dark matter halos relative to the Gaussian one is shown in the bottom panel.
This list demonstrates that a wide variety of researchers are needed to tackle this problem. Initially, the NG hub will bring together members of the Computational Cosmology MA to perform simulations, experts from the Dark Energy MA involved in the DES experiment, experimentalists from the KICP's CMB experiments (SPT and QUIET), center theorists, and external investigators to explore methods to determining primordial non-Gaussianity. As progress develops, hub membership is expected to attract an increasingly diverse set of scientists including string theorists working on inflation, observers interested in the relation between galaxies and their host halos, and many cosmologists with interests in between. By bringing together this diverse set of specialists to meetings and workshops, the hub intends to obtain reliable constraints on, or ideally to detect, primordial non-Gaussianity from DES as well as guide searches in the future.