Identify the underlying physics of inflation (inflaton field and potential)

Determine the physical mechanism responsible for the postulated inflationary epoch, including specifying the correct inflaton field and its potential V(φ), or an alternative microphysical account of accelerated early-universe expansion consistent with observations.

Background

Inflation explains the flatness and horizon problems and successfully predicts features of the cosmic microwave background, yet many inequivalent inflation models exist. The observed data underdetermine the inflaton’s identity and potential.

The book stresses that this uncertainty may be in-principle persistent, leaving the microphysics driving inflation unknown.

References

But there is also bad news. The data we now have, and maybe all the data we will ever have, leave wide open which of the many possible mechanisms — which sort of field φ, and which potential V(φ) — actually occurred. ... we do not know — and we may never know — the underlying physics of inflation.

— The Multiverse: a Philosophical Introduction  (2505.23639 - Butterfield, 29 May 2025) in Chapter 5, Section 3, item (3)

The questions of its ultraviolet completion, initial conditions, and embedding in a more fundamental theory remain unanswered.

— The alternative scalar field dark sector of the Universe: Cosmological inflation, quintessence and ekpyrotic model in the framework of scalar-tensor cosmology  (2609.37293 - Postolak, 29 Sep 2026) in Chapter 3, Section 3.1, Introduction

Nevertheless, several fundamental questions such as the nature of dark matter, the initial conditions of the Universe and the physics of inflation etc., remain open.

— Minkowski Functionals of CII Line Intensity Maps: Probing Astrophysics and Primordial Features  (2610.21710 - Acharya et al., 15 Oct 2026) in Section 1, Introduction