Constraints on a mixed inflaton and curvaton scenario for the generation of the curvature perturbation

Abstract

We consider a simple supersymmetric grand unified model which naturally solves the strong CP and µ problems via a Peccei-Quinn symmetry and leads to the standard realization of hybrid inflation. We show that the Peccei-Quinn field of this model can act as a curvaton. In contrast to the standard curvaton hypothesis, both the inflaton and the curvaton contribute to the total curvature perturbation. The model predicts the existence of an isocurvature perturbation too which has mixed correlation with the adiabatic one. The cold dark matter of the universe is mostly constituted by axions, which are produced at the QCD phase transition, plus a small amount of lightest sparticles. The predictions of the model are confronted with the first-year Wilkinson microwave anisotropy probe and other cosmic microwave background radiation data. We analyze in detail two representative choices of parameters for our model and derive bounds on the curvaton contribution to the adiabatic perturbation. We find that, for the choice which provides the best fitting of the data, the curvaton contribution to the amplitude of the adiabatic perturbation must be smaller than about 67% and the amplitude of the partial curvature perturbation from the curvaton smaller than 43.2 × 10 −5 (both at 95% confidence level). The best-fit power spectra are dominated by the adiabatic part of the inflaton contribution. We use Bayesian model comparison to show that this choice of parameters is disfavored with respect to the pure inflaton scale-invariant case with odds of about 50 to 1. For the second choice of parameters examined, the adiabatic mode is dominated by the curvaton, but this choice is strongly disfavored relative to the pure inflaton scale-invariant case (with odds of about 10 7 to 1). We conclude that in the present framework the perturbations must be dominated by the adiabatic component from the inflaton.

Bayes in the sky: Bayesian inference and model selection in cosmology

“…This is indeed the case, but the result is strongly dependent on the parameterization adopted for the isocurvature sector, which determines the strength of the Occam's razor effect. This is a consequence of the difficulty of coming up with a well motivated phenomenological parameterization of the isocurvature amplitudes, see the discussion in [58,182]. (ii) The shape of the primordial power spectrum has attracted considerable attention from a model comparison perspective [47,51,58,65,70,165,184,185].…”

“…The Bayesian model comparison approach based on the evaluation of the evidence is being increasingly applied to model building questions such as: are isocurvature contributions to the initial conditions required by the data [46,58,60,182]? Is the Universe flat [58,70,183]?…”

Indication for Primordial Anisotropies in the Neutrino Background from the Wilkinson Microwave Anisotropy Probe and the Sloan Digital Sky Survey

“…The MC convergence diagnostics is done along the lines described in [19]. In addition to the CMB data, we also consider the constraints on the real-space power spectrum of galaxies from the SLOAN galaxy redshift survey (SDSS) [20].…”

Mixed inflaton and spectator field models: CMB constraints and μ distortion

“…Thus it is possible that, for example, fluctuations sourced by one field dominate on large scales, while those from another scalar field can give a significant #1 Such mixed models have been investigated in the curvaton case in [7][8][9][10][11][12][13][14], in modulated reheating [15] as well as in the case of a general spectator field [13,16]. contribution on smaller scales.…”