$\phi^4$ inflation is not excluded

TL;DR

This paper demonstrates that the $$ inflation model is not ruled out by current data by providing counterexamples where primordial fluctuations originate at the start of slow-roll inflation, challenging previous exclusions.

Contribution

It introduces a new initial condition setup for $$ inflation, showing it can produce observationally consistent primordial fluctuations.

Findings

Counterexamples show $$ inflation is compatible with data.

Primordial power spectrum can violate scale-invariance yet match observations.

Different initial conditions from chaotic inflation are crucial for these results.

Abstract

We present counter examples to the claim that the $\lambda \phi^4$ inflaton potential is excluded by recent cosmological data. Finding counter examples requires that the actually observed primordial fluctuations are generated at the onset of the slow-roll regime of inflation. This set up for the initial conditions is therefore different from the usual scenario of chaotic inflation where inflation starts long before the observed fluctuations are created. The primordial power spectrum of "just enough" chaotic inflation violates scale-invariance in a way consistent with observations.