A Measurement of Cubic-Order Primordial Non-Gaussianity (g_{NL} and \tau_{NL}) With WMAP 5-Year Data

TL;DR

This paper analyzes WMAP 5-year data to measure higher-order primordial non-Gaussianity parameters, significantly improving constraints on au_{NL} and g_{NL} and exploring their relation to bispectrum amplitude.

Contribution

It introduces a new measurement approach for cubic-order non-Gaussianity parameters using WMAP data, providing tighter constraints than previous studies.

Findings

Constraints on g_{NL} between -7.4 and 8.2 in units of 10^5.

Constraints on au_{NL} between -0.6 and 3.3 in units of 10^4.

The ratio au_{NL}/(6f_{NL}/5)^2 ranges from -3 to 21 at 95% confidence.

Abstract

We measure two higher-order power spectra involving weighted cubic and squared temperature anisotropy maps from WMAP 5-year data to study the trispectrum generated by primordial non-Gaussianity. Using these measurements combined with Gaussian and noise simulations, we constrain the cubic order non-Gaussianity parameters \tau_{NL}, and g_{NL}. With V+W-band data out to l_{max}=600, we find -7.4 < g_{\rm NL}/10^5 < 8.2 and -0.6 < \tau_{\rm NL}/10^4 < 3.3 improving the previous COBE-based limit on \tau_{\rm NL} < 10^8 nearly four orders of magnitude with WMAP. We find that the ratio of trispectrum to bispectrum amplitude as captured by the ratio of \tau_{\rm Nl}/(6f_{\rm NL}/5)^2 ranges from -3 to 21 at the 95% confidence level.