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.
Solid Inflation
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abstract
We develop a cosmological model where primordial inflation is driven by a 'solid', defined as a system of three derivatively coupled scalar fields obeying certain symmetries and spontaneously breaking a certain subgroup of these. The symmetry breaking pattern differs drastically from that of standard inflationary models: time translations are unbroken. This prevents our model from fitting into the standard effective field theory description of adiabatic perturbations, with crucial consequences for the dynamics of cosmological perturbations. Most notably, non-gaussianities in the curvature perturbations are unusually large, with f_NL ~ 1/(\epsilon.c_s^2), and have a novel shape: peaked in the squeezed limit, with anisotropic dependence on how the limit is approached. Other unusual features include the absence of adiabatic fluctuation modes during inflation---which does not impair their presence and near scale-invariance after inflation---and a slightly blue tilt for the tensor modes.
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A transient parity-violating phase during inflation generates a robust blue-tilted (n_T ≃ 2) primordial gravitational wave spectrum at small scales with nearly maximal helicity coherence and linear polarization, offering a cosmological template for PTA data distinct from astrophysical sources.
Updated Planck CMB measurements give ns = 0.9649 ± 0.0042, r < 0.056, confirm flatness at 0.4 percent, and show no evidence for scale-dependent features or non-slow-roll dynamics in the inflaton potential.
Presents the science case, reference design, and project plan for the CMB-S4 ground-based CMB experiment.
citing papers explorer
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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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Transient Parity Violation during Inflation: Implications for PTA Gravitational Waves
A transient parity-violating phase during inflation generates a robust blue-tilted (n_T ≃ 2) primordial gravitational wave spectrum at small scales with nearly maximal helicity coherence and linear polarization, offering a cosmological template for PTA data distinct from astrophysical sources.
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Planck 2018 results. X. Constraints on inflation
Updated Planck CMB measurements give ns = 0.9649 ± 0.0042, r < 0.056, confirm flatness at 0.4 percent, and show no evidence for scale-dependent features or non-slow-roll dynamics in the inflaton potential.
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CMB-S4 Science Case, Reference Design, and Project Plan
Presents the science case, reference design, and project plan for the CMB-S4 ground-based CMB experiment.