Non-Gaussianities due to Relativistic Corrections to the Observed Galaxy Bispectrum

High-precision constraints on primordial non-Gaussianity (PNG) will significantly improve our understanding of the physics of the early universe. Among all the subtleties in using large scale structure observables to constrain PNG, accounting for relativistic corrections to the clustering statistics is particularly important for the upcoming galaxy surveys covering progressively larger fraction of the sky. We focus on relativistic projection effects due to the fact that we observe the galaxies through the light that reaches the telescope on perturbed geodesics. These projection effects can give rise to an effective $f_{\rm NL}$ that can be misinterpreted as the primordial non-Gaussianity signal and hence is a systematic to be carefully computed and accounted for in modelling of the bispectrum. We develop the technique to properly account for relativistic effects in terms of purely observable quantities, namely angles and redshifts. We give some examples by applying this approach to a subset of the contributions to the tree-level bispectrum of the observed galaxy number counts calculated within perturbation theory and estimate the corresponding non-Gaussianity parameter, $f_{\rm NL}$, for the local, equilateral and orthogonal shapes. For the local shape, we also compute the local non-Gaussianity resulting from terms obtained using the consistency relation for observed number counts. Our goal here is not to give a precise estimate of $f_{\rm NL}$ for each shape but rather we aim to provide a scheme to compute the non-Gaussian contamination due to relativistic projection effects. For the terms considered in this work, we obtain contamination of $f_{\rm NL}^{\rm loc} \sim {\mathcal O}(1)$.Comment: 31 pages, 6 figures, Typos corrected to match the published version in JCA

General conditions for scale-invariant perturbations in an expanding universe

We investigate the general properties of expanding cosmological models which generate scale-invariant curvature perturbations in the presence of a variable speed of sound. We show that in an expanding universe, generation of a super-Hubble, nearly scale-invariant spectrum of perturbations over a range of wavelengths consistent with observation requires at least one of three conditions: (1) accelerating expansion, (2) a speed of sound faster than the speed of light, or (3) super-Planckian energy density.Comment: 4 pages, RevTe

Probing Cosmic Origins with CO and Emission Lines

Primordial non-Gaussianity is an invaluable window into the physical processes that gave rise to the cosmological structure. The presence of local shape PNG imprints a distinct scale-dependent correction to the bias of dark matter tracers on large scales, which can be effectively probed via the technique of intensity mapping. Considering an upcoming generation of experiments, we demonstrate that intensity mapping of CO and [CII] emission can improve upon the current best constraints from the {\it Planck} satellite. We show that measurement of the CO intensity power spectrum by a hypothetical next stage of the ground-based COMAP experiment can achieve $\sigma(f_{\rm NL}^{\rm loc}) = 3.4$, and that the proposed CMB satellite mission PIXIE can achieve $\sigma(f_{\rm NL}^{\rm loc}) = 3.9$ via measurement of [CII] intensity power spectrum

Constraints on long-lived, higher-spin particles from the galaxy bispectrum

The presence of massive particles with spin during inflation induces distinct signatures on correlation functions of primordial curvature fluctuations. In particular, the bispectrum of primordial perturbations obtains an angular dependence determined by the spin of the particle, which can be used to set constraints on the presence of such particles. If these particles are long-lived on super-Hubble scales, as is the case, e.g., for partially massless particles, their imprint on correlation functions of curvature perturbations would be unsuppressed. In this paper, we make a forecast for how well such angular dependence can be constrained by the upcoming EUCLID spectroscopic survey via the measurement of the galaxy bispectrum

Inflaton or curvaton? Constraints on bimodal primordial spectra from mixed perturbations

We consider cosmic microwave background constraints on inflation models for which the primordial power spectrum is a mixture of perturbations generated by inflaton fluctuations and fluctuations in a curvaton field. If future experiments do not detect isocurvature modes or large non-Gaussianity, it will not be possible to directly distinguish inflaton and curvaton contributions. We investigate whether current and future data can instead constrain the relative contributions of the two sources. We model the spectrum with a bimodal form consisting of a sum of two independent power laws, with different spectral indices. We quantify the ability of current and upcoming data sets to constrain the difference Δn in spectral indices, and relative fraction f of the subdominant power spectrum at a pivot scale of k0=0.017  Mpc−1 h. Data sets selected are the WMAP 7-year data, alone and in conjunction with South Pole Telescope data, and a synthetic data set comparable to the upcoming Planck data set. We find that current data show no increase in quality of fit for a mixed inflaton/curvaton power spectrum, and a pure power-law spectrum is favored. The ability to constrain independent parameters such as the tensor/scalar ratio is not substantially affected by the additional parameters in the fit. Planck will be capable of placing significant constraints on the parameter space for a bimodal spectrum