Constraining running non-gaussianity

Abstract

The primordial non-Gaussian parameter fNL has been shown to be\nscale-dependent in several models of inflation with a variable speed of sound.\nStarting from a simple ansatz for a scale-dependent amplitude of the primordial\ncurvature bispectrum for two common phenomenological models of primordial\nnon-Gaussianity, we perform a Fisher matrix analysis of the bispectra of the\ntemperature and polarization of the Cosmic Microwave Background (CMB) radiation\nand derive the expected constraints on the parameter nNG that quantifies the\nrunning of fNL(k) for current and future CMB missions such as WMAP, Planck and\nCMBPol. We find that CMB information alone, in the event of a significant\ndetection of the non-Gaussian component, corresponding to fNL = 50 for the\nlocal model and fNL = 100 for the equilateral model of non-Gaussianity, is able\nto determine nNG with a 1-sigma uncertainty of Delta nNG = 0.1 and Delta nNG =\n0.3, respectively, for the Planck mission. In addition, we consider a Fisher\nmatrix analysis of the galaxy power spectrum to determine the expected\nconstraints on the running parameter nNG for the local model and of the galaxy\nbispectrum for the equilateral model from future photometric and spectroscopic\nsurveys. We find that, in both cases, large-scale structure observations should\nachieve results comparable to or even better than those from the CMB, while\nshowing some complementarity due to the different distribution of the\nnon-Gaussian signal over the relevant range of scales. Finally, we compare our\nfindings to the predictions on the amplitude and running of non-Gaussianity of\nDBI inflation, showing how the constraints on a scale-dependent fNL(k)\ntranslate into constraints on the parameter space of the theory.\n