Marilena LoVerde

Effects of scale-dependent non-Gaussianity on cosmological structures

The detection of primordial non-Gaussianity could provide a powerful means to test various inflationary scenarios. Although scale-invariant non-Gaussianity (often described by the fNL formalism) is currently best constrained by the CMB, single-field models with changing sound speed can have strongly scale-dependent non-Gaussianity. Such models could evade the CMB constraints but still have important effects at scales responsible for the formation of cosmological objects such as clusters and galaxies. We compute the effect of scale-dependent primordial non-Gaussianity on cluster number counts as a function of redshift, using a simple ansatz to model scale-dependent features. We forecast constraints on these models achievable with forthcoming datasets. We also examine consequences for the galaxy bispectrum. Our results are relevant for the Dirac–Born–Infeld model of brane inflation, where the scale dependence of the non-Gaussianity is directly related to the geometry of the extra dimensions.

CMB-S4 Science Book, First Edition

This book lays out the scientific goals to be addressed by the next-generation ground-based cosmic microwave background experiment, CMB-S4, envisioned to consist of dedicated telescopes at the South Pole, the high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras. CMB-S4 will dramatically advance cosmological studies by crossing critical thresholds in the search for the B-mode polarization signature of primordial gravitational waves, in the determination of the number and masses of the neutrinos, in the search for evidence of new light relics, in constraining the nature of dark energy, and in testing general relativity on large scales.

Extended Limber Approximation

We develop a systematic derivation for the Limber approximation to the angular cross-power spectrum of two random fields, as a series expansion in (l+1/2){sup -1}. This extended Limber approximation can be used to test the accuracy of the Limber approximation and to improve the rate of convergence at large ls. We show that the error in ordinary Limber approximation is O(l{sup -2}). We also provide a simple expression for the 2nd order correction to the Limber formula, which improves the accuracy to O(l{sup -4}). This correction can be especially useful for narrow redshift bins, or samples with small redshift overlap, for which the 0th order Limber formula has a large error. We also point out that using l instead of l+1/2, as is often done in the literature, spoils the accuracy of the approximation to O(l{sup -1})

Universal bound on N-point correlations from inflation.

Models of inflation in which non-Gaussianity is generated outside the horizon, such as curvaton models, generate distinctive higher-order correlation functions in the cosmic microwave background and other cosmological observables. Testing for violation of the Suyama-Yamaguchi inequality τ(NL) ≥ (6/5f (NL))(2), where f(NL) and f(NL) denote the amplitude of the three-point and four-point functions in certain limits, has been proposed as a way to distinguish qualitative classes of models. This inequality has been proved for a wide range of models, but only weaker versions have been proved in general. In this Letter, we give a proof that the Suyama-Yamaguchi inequality is always satisfied. We discuss scenarios in which the inequality may appear to be violated in an experiment such as Planck and how this apparent violation should be interpreted.

CMBPol Mission Concept Study: Gravitational Lensing

Gravitational lensing of the cosmic microwave background by large-scale structure in the late universe is both a source of cosmological information and a potential contaminant of primordial gravity waves. Because lensing imprints growth of structure in the late universe on the CMB, measurements of CMB lensing will constrain parameters to which the CMB would not otherwise be sensitive, such as neutrino mass. If the instrumental noise is sufficiently small (<~ 5 uK-arcmin), the gravitational lensing contribution to the large-scale B-mode will be the limiting source of contamination when constraining a stochastic background of gravity waves in the early universe, one of the most exciting prospects for future CMB polarization experiments. High-sensitivity measurements of small-scale B-modes can reduce this contamination through a lens reconstruction technique that separates the lensing and primordial contributions to the B-mode on large scales. A fundamental design decision for a future CMB polarization experiment such as CMBpol is whether to have coarse angular resolution so that only the large-scale B-mode (and the large-scale E-mode from reionization) is measured, or high resolution to additionally measure CMB lensing. The purpose of this white paper is to evaluate the science case for CMB lensing in polarization: constraints on cosmological parameters, increased sensitivity to the gravity wave B-mode via lens reconstruction, expected level of contamination from non-CMB foregrounds, and required control of beam systematics.

Testing Inflation with Large Scale Structure: Connecting Hopes with Reality

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

Local stochastic non-Gaussianity and N-body simulations

f_{\rm NL}^{\rm loc}

Halo bias in mixed dark matter cosmologies

(

Halo clustering and gNL-type primordial non-gaussianity

f_{\rm NL}^{\rm eq}

Non-Gaussian Mode Coupling and the Statistical Cosmological Principle

), natural target levels of sensitivity are