We present evidence for the detection of primordial non-Gaussianity of the local type (fNL), using the temperature information of the Cosmic Microwave Background (CMB) from the WMAP 3-year data. We employ the bispectrum estimator of non-Gaussianity described in [1] which allows us to analyze the entirety of the WMAP data without an arbitrary cut-off in angular scale. Using the combined information from WMAP's two main science channels up to ℓmax = 750 and the conservative Kp0 foreground mask we find 27 < fNL < 147 at 95% C.L., with a central value of fNL = 87. This corresponds to a rejection of fNL = 0 at more than 99.5% significance. We find that this detection is robust to variations in lmax, frequency and masks, and that no known foreground, instrument systematic, or secondary anisotropy explains our signal while passing our suite of tests. We explore the impact of several analysis choices on the stated significance and find 2.5 σ for the most conservative view. We conclude that the WMAP 3-year data disfavors canonical single field slow-roll inflation.PACS numbers:

We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to differentiate various inflationary mechanisms. In particular, a de tection of primordial B-mode polarization would demonstrate that inflation occurred at a very high energy scale, and that the inflaton traversed a super-Planckian distance in field space. We explain how such a detection or constraint would illuminate aspects of physics at the Planck scale. Moreover, CMB measurements can constrain the scale-dependence and non-Gaussianity of the primordial fluctuations and limit the possibility of a significant isocurvature contribution. Each such limit provides crucial information on the underlying inflationary dynamics. Finally, we quantify these considerations by presenting forecasts for the sensitivities of a future satellite experiment to the inflationary parameters. 10Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip. Striking advances in observational cosmology over the past two decades have provided us with a consistent account of the form and composition of the universe. Now that key cosmological parameters have been determined to within a few percent, we anticipate a generation of experiments that move beyond adding precision to measurements of what the universe is made of, but instead help us learn why the universe has the form we observe. In particular, during the coming decade, observational cosmology will probe the detailed dynamics of the universe in the earliest instants after the Big Bang, and start to yield clues about the physical laws that governed that epoch. Future experiments will plausibly reveal the dynamics responsible both for the large-scale homogeneity and flatness of the universe, and for the primordial seeds of small-scale inhomogeneities, including our own galaxy.The leading theoretical paradigm for the initial moments of the Big Bang is inflation [1][2][3][4][5][6], a period of rapid accelerated expansion. Inflation sets the initial conditions for conventional Big Bang cosmology by driving the universe towards a homogeneous and spatially flat configuration, which accurately describes the average state of the universe. At the same time, quantum fluctuations in both matter fields and spacetime produce minute inhomogeneities [7][8][9][10][11][12]. The seeds that grow into the galaxies, clusters of galaxies and the temperature anisotropies in the cosmic microwave background (CMB) are thus planted during the first moments of the universe's existence. By measuring the anisotropies in the microwave background and the large scale distribution of galaxies in the sky, we can infer the spectrum of the primordial perturbations laid down during inflation, and thus probe the underlying physics of this era. Any successful inflationary model will deliver a universe that is, on average, spatially flat and homogeneous -and one homogeneous universe looks very much like ano...

The primordial non-Gaussian parameter f NL has been shown to be scale-dependent in several models of inflation with a variable speed of sound, such as Dirac-Born-Infeld (DBI) models. Starting from a simple ansatz for a scale-dependent amplitude of the primordial curvature bispectrum for two common phenomenological models of primordial non-Gaussianity, we perform a Fisher matrix analysis of the bispectra of the temperature and polarization of the Cosmic Microwave Background (CMB) radiation and derive the expected constraints on the parameter n NG that quantifies the running of f NL (k) for current and future CMB missions such as WMAP, Planck and CMBPol. We find that CMB information alone, in the event of a significant detection of the non-Gaussian component, corresponding to f NL = 50 for the local model and f NL = 100 for the equilateral model of non-Gaussianity, is able to determine n NG with a 1-σ uncertainty of ∆n NG 0.1 and ∆n NG 0.3, respectively, for the Planck mission and a factor of two better for CMBPol. In addition, we consider a simple Fisher matrix analysis of the galaxy power spectrum to determine the expected constraints on the running parameter n NG for the local model and of the galaxy bispectrum for the equilateral model from future planned and proposed photometric and spectroscopic surveys. We find that, in both cases, large-scale structure observations should achieve results comparable to or even better than those from the CMB, while showing some complementarity due to the different distribution of the non-Gaussian signal over the relevant range of scales. Finally, we compare our findings to the predictions on the amplitude and running of non-Gaussianity of DBI inflation, showing how the constraints on a scale-dependent f NL (k) translate into constraints on the parameter space of the theory.