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Non-minimal coupling in light of ACT

Qing Gao, Yungui Gong, Zhu Yi, Fengge Zhang

Abstract

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 $Ω(φ) = 1 + ξf(φ)$ and the potential $V(φ) = λ^2 f^2(φ)$, we find that observational data constrain the parameters as $0.1 \lesssim ξ\lesssim 35$ and $0 \lesssim k \lesssim 1.5$ for $f(φ) = φ^k$ at the $1σ$ confidence level. With the help of the nonmiminal coupling $Ω(φ) = 1 + ξφ^2$, the hilltop inflation and power-law inflation models with power indices $2/3$ and $1/3$ can be consistent with observational data within the $1σ$ range. We also give the viable parameter regions for $ξ$ for these three models.

Non-minimal coupling in light of ACT

Abstract

The latest ACT data release disfavors the attractor . 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 and the potential , we find that observational data constrain the parameters as and for at the confidence level. With the help of the nonmiminal coupling , the hilltop inflation and power-law inflation models with power indices and can be consistent with observational data within the range. We also give the viable parameter regions for for these three models.

Paper Structure

This paper contains 6 sections, 24 equations, 2 figures.

Table of Contents

  1. introduction
  2. Nonminimal Inflation Model: Strong Coupling Limit
  3. Nonminimal coupling models
  4. General coupling function
  5. The nonminimal coupling with $\xi \phi^2$
  6. conclusion

Figures (2)

  • Figure 1: (Left) Scalar spectral index $n_s$ and tensor-to-scalar ratio $r$ predicted by the nonminimal coupling inflation model for various values of $k$ and $\xi$, compared with observational constraints. The contours are the $1\sigma$ and $2\sigma$ observational constraints from the P-ACT-LB data combined with B-mode measurements from the BICEP and Keck telescopes at the South Pole (BK18), referred to as P-ACT-LB-BK18. (Right) Corresponding parameter values of $\xi$ and $k$ consistent with observational bounds. The red and blue color region are the constraints from $1\sigma$ and $2\sigma$ observational constraints, respectively.
  • Figure 2: Scalar spectral index $n_s$ and tensor-to-scalar ratio $r$ for different models with the nonminimal coupling $\Omega(\phi)=1+\xi \phi^2$. The contour is the $1\sigma$ observational constraints from the P-ACT-LB-BK18 data. The various colored lines are for different models with varying $\xi$.