COBE-DMR constraints on the non-linear coupling parameter:: a wavelet based method

Non-linearity introduced in slow-roll inflation will produce weakly non-Gaussian cosmic microwave background (CMB) temperature fluctuations. We have simulated non-Gaussian large-scale CMB maps (including COBE-DMR constraints) introducing an additional quadratic term in the gravitational potential. The amount of non-linearity is controlled by the so-called non-linear coupling parameter f(nl). An analysis based on the Spherical Mexican Hat wavelet was applied to these and to the COBE-DMR maps. Skewness values obtained at several scales were combined into a Fisher discriminant. Comparison of the Fisher discriminant distributions obtained for different non-linear coupling parameters with the COBE-DMR values sets a constraint of \f(nl)\ < 1100 at the 68 per cent confidence level. This new constraint is tighter than the one previously obtained by using the bispectrum by Komatsu et al.