Are Inflationary Predictions Sensitive to Very High Energy Physics?

TL;DR

The paper investigates how inflationary predictions might be altered by very high-energy physics using a tractable hybrid-inflation model with a heavy scalar $\chi$. It shows that decoupling is largely maintained, but non-adiabatic oscillations of $\chi$ prior to horizon exit can imprint oscillatory modulations in the primordial power spectrum and CMB for a finite window of roughly $10$–$30$ $e$-foldings before horizon exit. A complementary, alternative model with a trilinear coupling $g'\chi\phi^2$ extends the observable window and yields different spectral features, including a maximum distortion at intermediate $k$. Collectively, the work confirms that CMB observations can meaningfully constrain high-energy physics without destroying the predictive power of standard inflation, while highlighting specific scenarios where small deviations may reveal trans-Planckian or other high-energy effects.

Abstract

It has been proposed that the successful inflationary description of density perturbations on cosmological scales is sensitive to the details of physics at extremely high (trans-Planckian) energies. We test this proposal by examining how inflationary predictions depend on higher-energy scales within a simple model where the higher-energy physics is well understood. We find the best of all possible worlds: inflationary predictions are robust against the vast majority of high-energy effects, but can be sensitive to some effects in certain circumstances, in a way which does not violate ordinary notions of decoupling. This implies both that the comparison of inflationary predictions with CMB data is meaningful, and that it is also worth searching for small deviations from the standard results in the hopes of learning about very high energies.