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

TL;DR

This work investigates a mixed inflaton-curvaton scenario in a supersymmetric LR GUT with Peccei-Quinn symmetry, where the PQ field acts as a curvaton alongside standard hybrid inflation. The total curvature perturbation is a weighted combination of inflaton and curvaton contributions, and isocurvature perturbations arise with mixed correlation to the adiabatic component, including axion, LSP, and baryon sectors. By computing the CMB power spectra and performing a full Bayesian analysis with WMAP1, CBI, and ACBAR data, the authors derive bounds on the curvaton contribution, finding that the adiabatic perturbation is predominantly inflaton-driven; the best-fitting parameter set yields a curvaton fraction F^{ad}_c ≈ 0.34 and an upper bound A_c ≲ 4.3×10^{-4} (95% c.l.), with Bayesian odds strongly disfavoring certain mixed scenarios relative to pure inflaton scale-invariant inflation. The results demonstrate that, despite the theoretical appeal of a curvaton component, current CMB data favor an inflation-dominated adiabatic perturbation, while highlighting how future observations could further probe mixed scenarios in particle-physics-motivated cosmologies.

Abstract

We consider a supersymmetric grand unified model which naturally solves the strong CP and mu 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 curvaton. In contrast to the standard curvaton hypothesis, both the inflaton and the curvaton contribute to the total curvature perturbation. The model predicts an isocurvature perturbation too which has mixed correlation with the adiabatic one. The cold dark matter of the universe is mostly constituted by axions plus a small amount of lightest sparticles. The predictions of the model are confronted with the Wilkinson microwave anisotropy probe and other cosmic microwave background radiation data. We analyze two representative choices of parameters 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 adiabatic amplitude must be smaller than about 67% (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 50 to 1. For the second choice of parameters, 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 10^7 to 1). We conclude that in the present framework the perturbations must be dominated by the adiabatic component from the inflaton.

Figures (16)

• Figure 1: The mass parameter $M$ versus $A_i$ for $\kappa=3\times 10^{-3}$ (solid line) or $3\times 10^{-2}$ (dashed line).
• Figure 2: The inflationary Hubble parameter $H_{\rm infl}$ versus $A_i$ for $\kappa=3\times 10^{-3}$ (solid line) or $3\times 10^{-2}$ (dashed line).
• Figure 3: The two green/lightly shaded bands in the $A_i-\phi_f$ plane which lead to the PQ vacua at $t_{\phi}$ for $\kappa=3\times 10^{-3}$, $\lambda=10^{-4}$ (model A). The white (not shaded) areas lead to the trivial vacuum and are thus excluded. The upper red/dark shaded area is excluded by the requirement that, at $t_*$, $V^{\prime\prime}\leq H_{\rm infl}^2$, while the lower one corresponds to the quantum regime. The blue/solid line shows the values of $A_i$, $\phi_f$ which approximately reproduce the correct value of the CMBR large scale temperature anisotropy, as measured by COBE (see Sec. \ref{['sec:toy']} for details).
• Figure 4: The two green/lightly shaded bands in the $A_i-\phi_f$ plane which lead to the PQ vacua at $t_{\phi}$ for $\kappa=3\times 10^{-2}$, $\lambda=10^{-4}$ (model B). The notation is the same as in Fig. \ref{['fig:model-4']}.
• Figure 5: Posterior marginalized pdf (normalized at peak value) for the amplitudes $A_i$, $A_c$ from our toy model for two choices of priors: flat priors (top panels), and Jeffreys' priors (bottom panels). The black line is for model A (upper green/lightly shaded band in Fig. \ref{['fig:model-4']}) and the cyan/light gray line for model B (upper green/lightly shaded band in Fig. \ref{['fig:model-5']}). The constraints on $A_i$, $A_c$ in model B and on $A_i$ in model A as well as the upper limit on $A_c$ in model A are robust with respect to the choice of priors. Compare the top panels with Fig. \ref{['fig:1dbase']}, which shows the results of the full MC analysis (with flat non-informative priors).