Local Primordial Non-Gaussianities and Super-Sample Variance

Fluctuations with wavelengths larger than the volume of a galaxy survey affect the measurement of the galaxy power spectrum within the survey itself. In the presence of local Primordial Non- Gaussianities (PNG), in addition to the super-sample matter density and tidal fluctuations, the large-scale gravitational potential also induces a modulation of the observed power spectrum. In this work we investigate this modulation by computing for the first time the response of the redshift-space galaxy power spectrum to the presence of a long wavelength gravitational potential, fully accounting for the stochastic contributions. For biased tracers new response functions arise due to couplings between the small-scale fluctuations in the density, velocity and gravitational fields, the latter through scale dependent bias operators, and the large-scale gravitational potential. We study the impact of the super-sample modes on the measurement of the amplitude of the primordial bispectrum of the local-shape, $f_{\rm NL}^{\rm loc}$, accounting for modulations of both the signal and the covariance of the galaxy power spectrum by the long modes. Considering DESI-like survey specifications, we show that in most cases super-sample modes cause little or no degradation of the constraints, and could actually reduce the errorbars on $f_{\rm NL}^{\rm loc}$ by (10 - 30)\%, if external information on the bias parameters is available.Comment: 15 pages, 4 figure

Comments on the Starobinsky Model of Inflation and its Descendants

We point out that the ability of some models of inflation, such as Higgs inflation and the universal attractor models, in reproducing the available data is due to their relation to the Starobinsky model of inflation. For large field values, where the inflationary phase takes place, all these classes of models are indeed identical to the Starobinsky model. Nevertheless, the inflaton is just an auxiliary field in the Jordan frame of the Starobinsky model and this leads to two important consequences: first, the inflationary predictions of the Starobinsky model and its descendants are slightly different (albeit not measurably); secondly the theories have different small-field behaviour, leading to different ultra-violet cut-off scales. In particular, one interesting descendant of the Starobinsky model is the non-minimally- coupled quadratic chaotic inflation. Although the standard quadratic chaotic inflation is ruled out by the recent Planck data, its non-minimally coupled version is in agreement with observational data and valid up to Planckian scales.Comment: 18 page