Primordial non-Gaussianity: local curvature method and statistical significance of constraints on fNL from WMAP data |
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Authors: | P. Cabella M. Liguori F. K. Hansen D. Marinucci S. Matarrese L. Moscardini N. Vittorio |
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Affiliation: | Dipartimento di Fisica, Universitàdi Roma 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133 Roma, Italy;Dipartimento di Fisica 'Galileo Galilei', Universitàdi Padova and INFN, Via Marzolo 8, I-35131 Padova, Italy;Dipartimento di Matematica, Universitàdi Roma 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133 Roma, Italy;Dipartimento di Astronomia, Universitàdi Bologna, Via Ranzani 1, I-40127 Bologna, Italy;INFN, Sezione di Roma 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133 Roma, Italy |
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Abstract: | We test the consistency of estimates of the non-linear coupling constant f NL using non-Gaussian cosmic microwave background (CMB) maps generated by the method described in the work of Liguori, Matarrese & Moscardini. This procedure to obtain non-Gaussian maps differs significantly from the method used in previous works on the estimation of f NL. Nevertheless, using spherical wavelets, we find results in very good agreement with Mukherjee & Wang, showing that the two ways of generating primordial non-Gaussian maps give equivalent results. Moreover, we introduce a new method for estimating the non-linear coupling constant from CMB observations by using the local curvature of the temperature fluctuation field. We present both Bayesian credible regions (assuming a flat prior) and proper (frequentist) confidence intervals on f NL, and discuss the relation between the two approaches. The Bayesian approach tends to yield lower error bars than the frequentist approach, suggesting that a careful analysis of the different interpretations is needed. Using this method, we estimate f NL=−10+270−260 at the 2σ level (Bayesian) and f NL=−10+310−270 (frequentist). Moreover, we find that the wavelet and the local curvature approaches, which provide similar error bars, yield approximately uncorrelated estimates of f NL and therefore, as advocated in the work of Cabella et al., the estimates may be combined to reduce the error bars. In this way, we obtain f NL=−5 ± 85 and f NL=−5 ± 175 at the 1σ and 2σ level respectively using the frequentist approach. |
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Keywords: | methods: numerical methods: statistical cosmic microwave background cosmology: observations cosmology: theory |
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