Non-minimal coupling of the inflaton to the Holst invariant in metric-affine gravity induces quasi-pole kinetics that generate an exponential plateau potential and Starobinsky-equivalent predictions regardless of the bare potential.
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Fractional attractors in light of the latest ACT observations
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abstract
In light of the latest results from ACT observations we review a class of potentials labeled as fractional attractors, that can originate from Palatini gravity. We show that, for certain choices of the scalar potential $V(\phi)$, the fractional attractors predict both a spectral index $n_s$ and a tensor-to-scalar ratio $r$ that fall within the $1\sigma$ region of the combined ACT+Planck data for a wide range of parameters. We also provide a numerical fit for the parameter space of this models in the case of a simple quadratic and quartic fractional potential.
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representative citing papers
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.
EDE models increase inferred α_s from CMB data, strengthening tension with USR PBH models that predict negative running.
Combining periodic non-minimal couplings to the Nieh-Yan term and Ricci scalar in metric-affine gravity makes natural inflation viable for sub-Planckian periodicity scales.
K-inflation with non-canonical kinetic term G(φ) shifts α-attractor T-models and natural inflation into the Planck-ACT-LB-BK18 allowed region while satisfying Swampland conjectures and producing testable GW spectra.
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.
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.
citing papers explorer
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Quasi-pole inflation in metric-affine gravity
Non-minimal coupling of the inflaton to the Holst invariant in metric-affine gravity induces quasi-pole kinetics that generate an exponential plateau potential and Starobinsky-equivalent predictions regardless of the bare potential.
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Harrison-Zeldovich attractor: From Planck to ACT results
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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Running into tension: primordial black holes from ultra-slow-roll inflation, spectral running, and the Hubble tension
EDE models increase inferred α_s from CMB data, strengthening tension with USR PBH models that predict negative running.
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Natural Metric-Affine Inflation: Reloaded
Combining periodic non-minimal couplings to the Nieh-Yan term and Ricci scalar in metric-affine gravity makes natural inflation viable for sub-Planckian periodicity scales.
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Reviving Motivated Inflationary Potentials with $K$-inflation in the light of ACT
K-inflation with non-canonical kinetic term G(φ) shifts α-attractor T-models and natural inflation into the Planck-ACT-LB-BK18 allowed region while satisfying Swampland conjectures and producing testable GW spectra.
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Testing $\alpha$-attractor P-model of inflation by Cosmic Microwave Background radiation
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.
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Induced-Gravity Palatini-Like Higgs Inflation in Supergravity Confronts ACT DR6
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.
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Curvaton-assisted hilltop inflation
Curvaton coupling relaxes initial tuning in hilltop inflation and revives the sub-Planckian quartic model while remaining consistent with cosmological observations.
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The implications of inflation for the last ACT
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.
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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.