Constraints on generating the primordial curvature perturbation and non-Gaussianity from instant preheating

TL;DR

The paper investigates whether inflationary isocurvature perturbations can be converted into the primordial curvature perturbation via instant preheating in two-field models. It analyzes three symmetry-breaking scenarios—nearly symmetric during inflation, strongly broken during inflation, and symmetric inflation followed by asymmetric preheating—deriving COBE normalization, preheat efficiency, and non-Gaussianity constraints for each. The results show that all approaches require fine-tuned initial conditions and typically yield small but sign-specific non-Gaussianity, with one scenario allowing modestly larger, positive $f_{NL}$; observational probes of $n_{\zeta}$, $r$, and $f_{NL}$ can test these restrictions. Overall, the work highlights the stringent conditions under which instant preheating can dominantly shape the primordial perturbations and emphasizes how future data can confirm or rule out these isocurvature-transfer scenarios.

Abstract

We analyse models of inflation in which isocurvature perturbations present during inflation are converted into the primordial curvature perturbation during instant preheating. This can be due to an asymmetry between the fields present either during inflation or during preheating. We consider all the constraints that the model must satisfy in order to be theoretically valid and to satisfy observations. We show that the constraints are very tight in all of the models proposed and special initial conditions are required for the models to work. In the case where the symmetry is strongly broken during inflation the non-Gaussianity parameter f_NL is generally large and negative.

Figures (2)

• Figure 1: The allowed parameter range of $g$ and $\log_{10}(\theta)$ for $m=10^{-7}M_{Pl}$. The rising thick red line is $\rho_{\psi}/\rho_{\sigma}=0.1$ with larger values below this line and the falling thin green line is $g\theta=0.00025$ which is the COBE constraint for $x=0.1$. Values with $x<0.1$ lie above this line. The shaded, textured area is the allowed region of parameter space.
• Figure 2: The allowed parameter range of $\phi_2$ and $m_1$. The curved red line is $\rho_{\psi}/\rho_{\sigma}=0.1$ with larger values to the left of the curve. The straight thick green lines mark constant values of $f_{NL}$ as marked on the diagram. The shaded, textured area corresponds to the allowed region where all of the constraints are satisfied. The vertical, blue lines mark values of constant $g$ as marked in the diagram.