Authors derive CMB power spectra from burst particle production in inflation, report a mild 2σ hint in joint Planck+ACT data for features on 3-10 Mpc scales, and show power-spectrum constraints outperform matched filters for lighter particles.
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ACT-ing on inflation: Implications of non Bunch-Davies initial condition and reheating on single-field slow roll models
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We investigate a class of slow roll inflationary models in the light of the recent Cosmic Microwave Background constraints from Planck 2018, ACT DR6, DESI DR1, and BICEP/\textit{Keck} 2018. The combined dataset favors a higher value of the scalar spectral index $n_{_\mathrm{S}}=0.9743 \pm 0.0034$, which places increased pressure on several conventional inflationary scenarios. In this study, we analyze the observational viability of various well-motivated models, including the $\alpha$-attractor E- and T-models, chaotic inflation, hilltop inflation, and natural inflation. We incorporate the effects of a post-inflationary phase of reheating and examine how the dynamics of reheating influence the predictions in the $n_{_\mathrm{S}}-r$ plane. We also impose a lower bound on the reheating temperature based on the constraint from the effective number of relativistic species ($\Delta{N}_{\mathrm{eff}}$) arising from primordial gravitational waves. While reheating improves agreement with observations for some models, significant regions of parameter space remain disfavored. Finally, we explore the impact of a non Bunch-Davies initial state and demonstrate that it can substantially improve the fit to the $n_{_\mathrm{S}}-r$ data across a broader class of inflationary models, thereby offering a potentially viable mechanism for reconciling theory with the latest observations.
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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.
SPT-3G delivers the most precise CMB EE and TE spectra at high multipoles to date, giving LCDM parameters with H0 = 66.66 ± 0.60 km/s/Mpc from ground-based data alone and reaching Planck-level constraints when combined with ACT.
NANOGrav data favors a blue-tilted tensor spectrum with nt ≈ 2.2, radiation-dominated reheating, and alpha-vacuum states over standard Bunch-Davies, with a frequency-dependent alpha suggested to resolve the blue-tilt tension.
Alpha-attractor quintessential inflation models are disfavored by DESI observations and Delta Neff limits from gravitational waves, as they predict an inconsistent scalar spectral index when the gravitational-wave abundance is constrained.
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.
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.
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.
F-term hybrid inflation with SU(1,1)/U(1) or SU(2)/U(1) Kähler geometry in GUTs can be realized without inflationary extrema for broad parameters, matching ACT/SPT data via curvature and tadpole adjustments while predicting cosmic string gravitational waves.
Long inflation screens Euclidean wormhole initial states from the CMB, turning them into Bunch-Davies predictions and providing a bound on inflationary duration via visibility limits on Bogoliubov excitations.
Unitarity-conserving Peccei-Quinn inflation agrees with ACT data within 1 sigma and allows axion decay constants up to 6.4e13 GeV without post-inflation symmetry restoration, unlike the conventional model.
citing papers explorer
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Probing inflationary particle production with the CMB power spectrum
Authors derive CMB power spectra from burst particle production in inflation, report a mild 2σ hint in joint Planck+ACT data for features on 3-10 Mpc scales, and show power-spectrum constraints outperform matched filters for lighter particles.
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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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SPT-3G D1: CMB temperature and polarization power spectra and cosmology from 2019 and 2020 observations of the SPT-3G Main field
SPT-3G delivers the most precise CMB EE and TE spectra at high multipoles to date, giving LCDM parameters with H0 = 66.66 ± 0.60 km/s/Mpc from ground-based data alone and reaching Planck-level constraints when combined with ACT.
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Constraints on the inflationary vacuum and reheating era from NANOGrav
NANOGrav data favors a blue-tilted tensor spectrum with nt ≈ 2.2, radiation-dominated reheating, and alpha-vacuum states over standard Bunch-Davies, with a frequency-dependent alpha suggested to resolve the blue-tilt tension.
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DESI and Gravitational Wave Constraints Challenge Quintessential {\alpha}-Attractor Inflation
Alpha-attractor quintessential inflation models are disfavored by DESI observations and Delta Neff limits from gravitational waves, as they predict an inconsistent scalar spectral index when the gravitational-wave abundance is constrained.
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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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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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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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F-Term Hybrid Inflation with T-Model K\"ahler Geometry and Beyond
F-term hybrid inflation with SU(1,1)/U(1) or SU(2)/U(1) Kähler geometry in GUTs can be realized without inflationary extrema for broad parameters, matching ACT/SPT data via curvature and tadpole adjustments while predicting cosmic string gravitational waves.
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Long Inflation Screens Euclidean-Wormhole Initial States
Long inflation screens Euclidean wormhole initial states from the CMB, turning them into Bunch-Davies predictions and providing a bound on inflationary duration via visibility limits on Bogoliubov excitations.
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Conventional and Unitarity-Conserving Peccei-Quinn Inflation Models and ACT
Unitarity-conserving Peccei-Quinn inflation agrees with ACT data within 1 sigma and allows axion decay constants up to 6.4e13 GeV without post-inflation symmetry restoration, unlike the conventional model.