Level Of Primordial non-Gaussianity Research Articles

Constraining primordial non-Gaussianity by combining next-generation galaxy and 21 cm intensity mapping surveys

Surveys of the matter distribution contain ‘fossil’ information on possible non-Gaussianity that is generated in the primordial Universe. This primordial signal survives only on the largest scales where cosmic variance is strongest. By combining different surveys in a multi-tracer approach, we can suppress the cosmic variance and significantly improve the precision on the level of primordial non-Gaussianity. We consider a combination of an optical galaxy survey, like the recently initiated DESI survey, together with a new and very different type of survey, a 21 cm intensity mapping survey, like the upcoming SKAO survey. A Fisher forecast of the precision on the local primordial non-Gaussianity parameter f_{textrm{NL}}, shows that this multi-tracer combination, together with non-overlap single-tracer information, can deliver precision comparable to that from the CMB. Taking account of the largest systematic, i.e. foreground contamination in intensity mapping, we find that sigma (f_{textrm{NL}}) sim 4.

Halo statistics in non-Gaussian cosmologies: the collapsed fraction, conditional mass function and halo bias from the path-integral excursion set method

Characterizing the level of primordial non-Gaussianity (PNG) in the initial conditions for structure formation is one of the most promising ways to test inflation and differentiate among different scenarios. The scale-dependent imprint of PNG on the large-scale clustering of galaxies and quasars has already been used to place significant constraints on the level of PNG in our observed Universe. Such measurements depend upon an accurate and robust theory of how PNG affects the bias of galactic halos relative to the underlying matter density field. We improve upon previous work by employing a more general analytical method - the path-integral extension of the excursion set formalism - which is able to account for the non-Markovianity caused by PNG in the random-walk model used to identify halos in the initial density field. This non-Markovianity encodes information about environmental effects on halo formation which have so far not been taken into account in analytical bias calculations. We compute both scale-dependent and -independent corrections to the halo bias, along the way presenting an expression for the conditional collapsed fraction for the first time, and a new expression for the conditional halo mass function. To leading order in our perturbative calculation, we recover the halo bias results of Desjacques et. al. (2011), including the new scale-dependent correction reported there. However, we show that the non-Markovian dynamics from PNG can lead to marked differences in halo bias when next-to-leading order terms are included. We quantify these differences here. [abridged]

Limits on primordial non-Gaussianity from Minkowski Functionals of theWMAPtemperature anisotropies

We present an analysis of the Minkowski Functionals (MFs) describing the Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr temperature maps to place limits on possible levels of primordial non-Gaussianity. In particular, we apply perturbative formulae for the MFs to give constraints on the usual non-linear coupling constant fNL. The theoretical predictions are found to agree with the MFs of simulated cosmic microwave background (CMB) maps including the full effects of radiative transfer. The agreement is also very good even when the simulation maps include various observational artefacts, including the pixel window function, beam smearing, inhomogeneous noise and the survey mask. We accordingly find that these analytical formulae can be applied directly to observational measurements of fNL without relying on non-Gaussian simulations. Considering the bin-to-bin covariance of the MFs in WMAP in a chi-square analysis, we find that the primordial non-Gaussianity parameter is constrained to lie in the range -70 < fNL < 91 [95 per cent confidence level (C.L.)] using the Q + V + W co-added maps.

Cosmic microwave background anisotropies at second order: I

We present the computation of the full system of Boltzmann equations at second orderdescribing the evolution of the photon, baryon and cold dark matter fluids. These equationsallow one to follow the time evolution of the cosmic microwave background anisotropies atsecond order at all angular scales from the early epoch, when the cosmologicalperturbations were generated, to the present, through the recombination era. Thispaper sets the stage for the computation of the full second-order radiation transferfunction at all scales and for a generic set of initial conditions specifying the level ofprimordial non-Gaussianity. In a companion paper, we will present the computation ofthe three-point correlation function at recombination which is very relevant forthe issue of non-Gaussianity in the cosmic microwave background anisotropies.

The full second-order radiation transfer function for large-scale CMB anisotropies

We calculate the full second-order radiation transfer function for cosmic microwavebackground anisotropies on large angular scales in a flat universe filled with matterand cosmological constant. It includes (i) the second-order generalization of theSachs–Wolfe effect, and of (ii) both the early and late integrated Sachs–Wolfe effects,and (iii) the contribution of the second-order tensor modes, and is valid for ageneric set of initial conditions specifying the level of primordial non-Gaussianity.