Hunting for primordial non-Gaussianity in the cosmic microwave background
Abstract
Since the first limit on the (local) primordial non-Gaussianity parameter, fNL, was obtained from the Cosmic Background Explorer (COBE) data in 2002, observations of the cosmic microwave background (CMB) have been playing a central role in constraining the amplitudes of various forms of non-Gaussianity in primordial fluctuations. The current 68% limit from the 7-year data of the Wilkinson Microwave Anisotropy Probe (WMAP) is fNL = 32 ± 21, and the Planck satellite is expected to reduce the uncertainty by a factor of 4 in a few years from now. If fNL Gt 1 is found by Planck with high statistical significance, all single-field models of inflation would be ruled out. Moreover, if the Planck satellite finds fNL ~ 30, then it would be able to test a broad class of multi-field models using the 4-point function (trispectrum) test of τNL >= (6fNL/5)2. In this paper, we review the methods (optimal estimator), results (WMAP 7-year) and challenges (secondary anisotropy, second-order effect and foreground) of measuring primordial non-Gaussianity from the CMB data, present a science case for the trispectrum and conclude with future prospects.
- Publication:
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Classical and Quantum Gravity
- Pub Date:
- June 2010
- DOI:
- 10.1088/0264-9381/27/12/124010
- arXiv:
- arXiv:1003.6097
- Bibcode:
- 2010CQGra..27l4010K
- Keywords:
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- Astrophysics - Cosmology and Nongalactic Astrophysics;
- General Relativity and Quantum Cosmology;
- High Energy Physics - Phenomenology;
- High Energy Physics - Theory
- E-Print:
- 33 pages, 4 figures. Invited review, accepted for publication in the CQG special issue on nonlinear cosmological perturbations. (v2) References added. More clarifications are added to the second-order effect and the multi-field consistency relation, tauNL>