What new physics can we extract from inflation using the ACT DR6 and DESI DR2 Observations?

TL;DR

Upcoming CMB and gravitational wave experiments will significantly constrain inflationary models by precisely measuring spectral parameters, potentially excluding several popular models and providing insights into the microphysics of inflation.

Contribution

This paper provides a comprehensive forecast of how future observations will test and distinguish among a wide range of inflationary theories using spectral parameter measurements.

Findings

Next-generation data will sharply constrain the scale dependence of the scalar power spectrum.

Several well-studied inflation models are forecasted to be excluded at high significance.

Measurement of $eta_s$ and $ riangle\,phi$ can diagnose kinetic structure and UV sensitivity.

Abstract

We present a comprehensive analysis of inflationary models in light of projected sensitivities from forthcoming CMB and gravitational wave experiments, incorporating data from recent ACT DR6, DESI DR2, CMB-S4, LiteBIRD, and SPHEREx. Focusing on precise predictions in the $(n_s, \alpha_s, \beta_s)$ parameter space, we evaluate a broad class of inflationary scenarios -- including canonical single-field models, non-minimally coupled theories, and string-inspired constructions such as Starobinsky, Higgs, Hilltop, $\alpha$-attractors, and D-brane models. Our results show that next-generation observations will sharply constrain the scale dependence of the scalar power spectrum, elevating $\alpha_s$ and $\beta_s$ as key discriminants between large-field and small-field dynamics. Strikingly, several widely studied models -- such as quartic Hilltop inflation and specific DBI variants -- are forecast to be excluded at high significance. We further demonstrate that the combined measurement of $\beta_s$ and the field excursion $\Delta\phi$ offers a novel diagnostic of kinetic structure and UV sensitivity. These findings underscore the power of upcoming precision cosmology to probe the microphysical origin of inflation and decisively test broad classes of theoretical models.