Nonminimal derivative coupling realizes the Harrison-Zeldovich attractor for monomial, hilltop, and α-attractor E-models, pulling them to the scale-invariant spectrum suggested by ACT data.
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Starobinsky like inflation and EGB Gravity in the light of ACT
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abstract
The ACT data shows an enhancement in the value of the scalar spectral index, as $n_s = 0.9743 \pm 0.0034$, leading to disfavoring many inflationary models, including the Starobinsky model. To satisfy the constraint made by ACT, we will investigate the Starobinsky potential within the Einstein-Gauss-Bonnet(EGB) gravity theory. EGB gravity is motivated by the higher-dimensional theory, which includes quadratic curvature correction terms and a coupling between the scalar field and the GB term that modifies the dynamical equations. The model is considered by using the slow-roll approximation method and the exact numerical approach for two different coupling functions. The results indicate that the model is in good agreement with the data and the results stand in $1\sigma$ of the ACT $r-n_s$ plane. Considering the running of the scalar spectral index also implies the consistency of the model with data. In addition, the parametric space of the free parameters of the EGB coupling is explored, where we find the acceptable region of the parameters in which the resulting $n_s$ and $r$ stay in $1\sigma$ of the ACT data. Next, the reheating phase is considered. It is determined that the model can simultaneously satisfy the constraint of ACT data and the reheating temperature constraints.
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background 7representative citing papers
Minimal setup with one RHN and Higgs inflaton generates neutrino masses, baryon asymmetry via Affleck-Dine leptogenesis, and matches PLANCK/ACT inflation data with a small parameter space.
Simulations in Einstein-scalar-Gauss-Bonnet gravity show oscillons form with similar properties to standard cases but trigger EFT breakdown for large couplings via high local curvatures.
EDE models increase inferred α_s from CMB data, strengthening tension with USR PBH models that predict negative running.
Polynomial α-attractor P-models of inflation accommodate Planck and Planck+ACT CMB data for ranges of reheating temperatures when decays and fragmentation are included.
A Palatini-supergravity Higgs-inflation model with induced gravity predicts a scalar spectral index ns≈0.972-0.974, consistent with ACT DR6, and favors split supersymmetry with gravitino mass 40-60 PeV.
An R^3 modification to R^2-Higgs inflation fits the high n_s by inducing Goldstone preheating that reconciles CMB and inflationary energy scales.
Curvaton coupling relaxes initial tuning in hilltop inflation and revives the sub-Planckian quartic model while remaining consistent with cosmological observations.
A parameterized slow-roll model and a new exponential f(R) inflation model are constrained by P-ACT-LB-BK18 data, with the latter aligning to the ACT scalar spectral index preference in both standard and EDE frameworks.
Non-Bunch-Davies initial conditions substantially improve the fit of various single-field slow-roll inflation models to updated n_s-r constraints from ACT DR6 combined with Planck, DESI, and BICEP/Keck data.
Exponential and sech Gauss–Bonnet couplings restore ACT-compatible ns and r for quintessential inflation, while tanh fails for a structural sign reason; reheating remains BBN-safe.
A power-law non-canonical kinetic coupling F(φ)=1+Aφ^n revives the Starobinsky inflation potential's consistency with ACT DR6 CMB data while preserving attractor dynamics and yielding viable reheating.
Dimension-six operators |Φ|²R² and |Φ|⁴R in R²-Higgs inflation accommodate enhanced n_s from CMB+BAO data and enable rapid preheating via Goldstone modes.
Four Einstein-Gauss-Bonnet inflationary models are reconstructed from a chosen tensor-to-scalar ratio and shown to satisfy ACT and GW170817 constraints including scalar perturbation amplitude.
Einstein-Gauss-Bonnet inflation can yield positive spectral-index running with a viable era under ACT-like hints, while scalar-field and F(R) models largely cannot.
MCMC analysis of sixteen ghost-free f(R,G) inflation models shows all reproduce ns ≈ 0.97 at 60 e-folds with stable μ ≈ 0.1, preference set by Hubble parametrization.
MCMC fitting of joint P-ACT-LB-BK18 dataset constrains non-canonical parameter alpha to 8.8, 11.7, and 16.4 (1 sigma) for chaotic inflation potentials with n=1/3, 2/3, 1 respectively.
Updated constraints on non-zero VEV parameter M from ACT+Planck data, plus lattice simulations showing oscillon formation and reheating implications.
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Curvaton-assisted hilltop inflation
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The implications of inflation for the last ACT
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ACT-ing on inflation: Implications of non Bunch-Davies initial condition and reheating on single-field slow roll models
Non-Bunch-Davies initial conditions substantially improve the fit of various single-field slow-roll inflation models to updated n_s-r constraints from ACT DR6 combined with Planck, DESI, and BICEP/Keck data.
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Constraining Quintessential Inflation with ACT: A Gauss-Bonnet Gateway
Exponential and sech Gauss–Bonnet couplings restore ACT-compatible ns and r for quintessential inflation, while tanh fails for a structural sign reason; reheating remains BBN-safe.
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Starobinsky Inflation in k-Essence Framework: Attractor Dynamics, Reheating, and Consistency with ACT DR6
A power-law non-canonical kinetic coupling F(φ)=1+Aφ^n revives the Starobinsky inflation potential's consistency with ACT DR6 CMB data while preserving attractor dynamics and yielding viable reheating.
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Nonminimal couplings and preheating effects in $R^2$-Higgs inflation after ACT and SPT
Dimension-six operators |Φ|²R² and |Φ|⁴R in R²-Higgs inflation accommodate enhanced n_s from CMB+BAO data and enable rapid preheating via Goldstone modes.
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Reconstructing ACT-compatible and GW170817-compatible Einstein-Gauss-Bonnet Inflation from the Observational Indices
Four Einstein-Gauss-Bonnet inflationary models are reconstructed from a chosen tensor-to-scalar ratio and shown to satisfy ACT and GW170817 constraints including scalar perturbation amplitude.
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ACT Data and Positive Running of the Spectral Index for Scalar Theory and Modified Gravity
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String-inspired Gauss-Bonnet Gravity Inflation and ACT
MCMC analysis of sixteen ghost-free f(R,G) inflation models shows all reproduce ns ≈ 0.97 at 60 e-folds with stable μ ≈ 0.1, preference set by Hubble parametrization.
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Constraints on non-canonical chaotic inflation from ACT DR6 and BICEP/Keck data
MCMC fitting of joint P-ACT-LB-BK18 dataset constrains non-canonical parameter alpha to 8.8, 11.7, and 16.4 (1 sigma) for chaotic inflation potentials with n=1/3, 2/3, 1 respectively.
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