Theoretical uncertainties in inflationary predictions

Abstract

With present and future observations becoming of higher and higher quality, it is timelyand necessary to investigate the most significant theoretical uncertainties in the predictionsof inflation. We show that our ignorance of the entire history of the universe, including thephysics of reheating after inflation, translates to considerable errors in observationally relevantparameters. Using the inflationary flow formalism, we estimate that for a spectral indexn and tensor/scalarratio r in the region favoured by current observational constraints, the theoretical errors are of orderΔn/|n−1| ∼ 0.1–1 and Δr/r ∼ 0.1–1. These errors represent the dominant theoretical uncertainties in the predictions ofinflation, and are generically of the order of or larger than the projected uncertainties infuture precision measurements of the cosmic microwave background. We also show that thelowest order classification of models into small field, large field and hybrid breaks downwhen higher order corrections to the dynamics are included. Models can flow from oneregion to another.