Effects and detectability of quasi-single field inflation in the large-scale structure and cosmic microwave background

Abstract

Quasi-single field inflation predicts a peculiar momentum dependence in the squeezed limit of the primordial bispectrum which smoothly interpolates between the local and equilateral models. This dependence is directly related to the mass of the isocurvatons in the theory which is determined by the supersymmetry. Therefore, in the event of detection of a non-zero primordial bispectrum, additional constraints on the parameter controlling the momentum-dependence in the squeezed limit becomes an important question. We explore the effects of these non-Gaussian initial conditions on large-scale structure and the cosmic microwave background, with particular attention to the galaxy power spectrum at large scales and scale-dependence corrections to galaxy bias. We determine the simultaneous constraints on the two parameters describing the QSF bispectrum that we can expect from upcoming large-scale structure and cosmic microwave background observations. We find that for relatively large values of the non-Gaussian amplitude parameters, but still well within current uncertainties, galaxy power spectrum measurements will be able to distinguish the QSF scenario from the predictions of the local model. A CMB likelihood analysis, as well as Fisher matrix analysis, shows that there is also a range of parameter values for which Planck data may be able distinguish between QSF models and the related local and equilateral shapes. Given the different observational weightings of the CMB and LSS results, degeneracies can be significantly reduced in a joint analysis.

Anomalous dimensions and non-gaussianity

“…Similar constraints arise in other models involving a linear mixing with the inflaton (e.g. [9][10][11][31][32][33][34]). …”

“…These correlators are different from those that arise in the weakly coupled massive fields [9][10][11][12]; the position space two point function for massive fields is a nontrivial hypergeometric function, distinct from the simpler function (2.4) except for the special case of a conformally coupled free scalar.…”

“…Moreover, interesting powerlaw deviations from this shape of non-Gaussianity arise for fields of nonzero mass m [9][10][11] ζ k 1 ζ k 2 ζ k 3 = B(k 1 , k 2 , k 3 ) (2π) 3 δ (3) (k 1 + k 2 + k 3 ) (1.2) …”

“…Non-Guassianities from our conformally coupled sector are able to generate a scale dependent bias in the different interval 0 ≤ α = 2−∆ ≤ 1: in a sense, they allow us to fill the whole range. While a detection of the non-Gaussianity induced by these operators can be clearly within reach, the actual detection of these smaller values of α in the data seems to be quite hard; see [43,44] for first forecasts using the scale dependent bias of the power spectrum of galaxies. It would be interesting to see if the prospects of detection will improve upon inclusion in the forecasts of the bispectrum of galaxies, as it was done for local non-Gaussianities in [42], as well as of techniques that tend to reduce the cosmic variance [45].…”

Inflation and String Theory

“…1 These fields fluctuation quantum-mechanically during inflation and therefore have to be included in the computation of the primordial perturbations. The phenomenology of these models of quasisingle-field inflation [490] has been explored in [118,207,208,239,255,265,267,[491][492][493][494][495][496][497].…”