Natural Supergravity inflation

TL;DR

This work proposes a mechanism for natural inflation within supergravity by exploiting moduli-driven kinetic-term symmetries to produce an infrared fixed point that cancels the dangerous quadratic inflaton term, enabling a prolonged slow-roll without fine tuning. The resulting inflationary potential yields a tilted scalar spectrum with negligible gravitational waves, consistent with COBE normalization and large-scale structure observations for a cold dark matter universe. The model predicts a COBE-normalized scale $\Lambda/M \sim 2.8\times10^{-4}$ (modulo $|\gamma|^{-1/2}$) and a CMB angular power spectrum with suppressed Doppler peaks, offering a clear falsifiable signature for upcoming measurements. Overall, it provides a testable link between supergravity dynamics, moduli physics, and observable cosmological perturbations, potentially obviating the need for hot dark matter components.

Abstract

We identify a new mechanism in supergravity theories which leads to successful inflation without any need for fine tuning. The simplest model yields a spectrum of density fluctuations tilted away from scale-invariance and negligible gravitational waves. We demonstrate that this is consistent with the observed large-scale structure for a cold dark matter dominated, critical density universe. The model can be tested through measurements of microwave background anisotropy on small angular scales.

Figures (3)

• Figure 1: Predicted power spectrum of density fluctuations in cold dark matter compared with data from the APM survey. The dotted line shows the linear spectrum, and the dashed lines the non-linear evolution according to two different prescriptions. The spectra are normalized to COBE adopting (a) $N_{\rm COBE}=51,\ \Omega_{\rm N}=0.05,\ h=0.4$, and (b) $N_{\rm COBE}=31,\ \Omega_{\rm N}=0.1,\ h=0.5$.
• Figure 2: Predicted value of the variance of the density field smoothed over a sphere of radius $8\,h^{-1}$ Mpc for (a) $N_{\rm COBE}=51$ and (b) $N_{\rm COBE}=31$, as a function of the Hubble parameter and the nucleon density parameter. The region within the marked contours is consistent with the observational limits (horizontal planes) inferred from rich clusters of galaxies.
• Figure 3: Predicted angular power spectrum of CMB anisotropy normalized to COBE and compared with current data, adopting (a) $\Omega_{\rm N}=0.05$, and (b) $\Omega_{\rm N}=0.1$, both with $h=0.5$. The standard scale-invariant spectrum (full line) is compared with the tilted spectra from supergravity inflation for $N_{\rm COBE}=51$ (dashed line) and $N_{\rm COBE}=31$ (dotted line).