Non-minimal coupling in light of ACT

Understand

The latest ACT data release disfavors the attractor $n_s=1-2/N$.

• In inflationary models with nonminimal coupling, such attractors typically arise in the strong coupling limit.
• To align with observational constraints, we focus on nonminimal coupling models with small coupling constants.
• For the model with the coupling function $\Omega(\phi) = 1 + \xi f(\phi)$ and the potential $V(\phi) = \lambda^2 f^2(\phi)$, we find that observational data constrain the parameters as $0.1 \lesssim \xi \lesssim 35$ and $0 \lesssim k \lesssim 1.5$ for $f(\phi) = \phi^k$ at the $1\sigma$ confidence level.