Gravitational Wave Background and Non-Gaussianity as a Probe of the Curvaton Scenario

TL;DR

The paper investigates how the stochastic gravitational wave background and non-Gaussianity can test the curvaton mechanism for generating primordial density perturbations. It derives how GW spectra are modified by curvaton-induced entropy production and how curvaton fluctuations set the curvature perturbation and tensor-to-scalar ratio, including a consistency relation between $n_s$ and $n_t$. It also links the non-Gaussianity parameter $f_{\rm NL}$ to the curvaton abundance at decay, highlighting complementary observational handles from CMB and space-based GW detectors. The work demonstrates that DECIGO/BBO, in combination with CMB measurements, can exhaust the curvaton parameter space and constrain its decay history and energy scale, providing a window into high-energy physics inaccessible to terrestrial experiments.

Abstract

We study observational implications of the stochastic gravitational wave background and a non-Gaussian feature of scalar perturbations on the curvaton mechanism of the generation of density/curvature fluctuations, and show that they can determine the properties of the curvaton in a complementary manner to each other. Therefore even if Planck could not detect any non-Gaussianity, future space-based laser interferometers such as DECIGO or BBO could practically exhaust its parameter space.

Figures (2)

• Figure 1: (Top) Spectra of the gravitational wave background for inflationary scale $H_{\rm inf}=10^{14}$ GeV and $10^{13}$ GeV. Here we have taken $T_{\rm R}=10^7$ GeV. Also shown are sensitivities of planned space-based gravitational wave detectors, DECIGO with a correlation analysis (blue dashed line), ultimate-DECIGO (purple dotted line), and correlation of analysis of ultimate-DECIGO (red dot-dashed line). (Bottom) Same as the top panel for the dilution factor $F=10$ for $T_\sigma$=10 GeV and $T_{\rm R}=10^7$ GeV.
• Figure 2: Range of the curvaton parameters $\sigma_i/M_{\rm Pl}$- $T_\sigma/T_{\rm R}$ which can be probed by space-based laser interferometers. The upper panel represents the case with single ultimate-DECIGO and B-mode measurements down to $r=10^{-3}$, while the lower panel shows an ideal case with correlation analysis of ultimate-DECIGO and B-mode measurements accesible to $r=2\times 10^{-6}$. Region above the red wedge is excluded since the tensor mode contribution to the CMB anisotropy becomes too large. Also shown there are contours of the non-linearity parameter $f_{\rm NL}$. Upper left region above the solid line is disfavored by WMAP. In the green region all the curvaton parameters can be determined in terms of $f_{\rm NL}$ and $r$, while in the orange region they can be determined by $F$ and $r$ provided other sources of entropy production is absent. In the yellow region, $F$ and $r$ are not determined independently, and only the combination $rF^{-4/3}$ is determined.