Single-Field Inflation After WMAP5

TL;DR

This work tests single-field inflation against the WMAP5+BAO+SN data under instantaneous reheating, comparing canonical and non-canonical (DBI) scenarios and exploring wrapped and multi-brane UV configurations in warped geometries. Using observables such as the scalar spectral index $n_s$, tensor-to-scalar ratio $r$, and non-Gaussianity $f_{NL}$, it finds that modular/new inflation with small self-interaction powers is tightly constrained, the cubic case is disfavored for $N<60$, and the intermediate inflation model lies outside the 1σ region across powers. The analysis shows that warped throat parameters are strongly limited by observations in all DBI scenarios, including wrapped D5/D7 and multi-brane setups, often requiring smaller $\mathrm{Vol}(X_5)/N$ or new Calabi–Yau four-fold geometries. Collectively, the results highlight stringent geometric and model-building constraints on string-theory-inspired single-field inflation and point to the potential of future observations to break degeneracies between canonical and non-canonical scenarios, especially through tensor modes and precise $n_s$ measurements.

Abstract

Single-field models of inflation are analysed in light of the WMAP five-year data. Assuming instantaneous reheating, we find that modular/new inflation models with small powers in the effective inflaton self-interaction are more strongly constrained than previously. The model with a cubic power lies outside the 2 sigma regime when the number of e-folds is less than 60. We also find that the predictions for the intermediate model of inflation do not overlap the 1 sigma region regardless of the power of the monomial potential. We analyse a number of ultra-violet, DBI braneworld scenarios involving both wrapped and multiple-brane configurations, where the inflaton kinetic energy is close to the maximum allowed by the warped geometry. In all cases, we find that the parameters of the warped throat are strongly constrained by observations.