An open quantum system treatment of curvature perturbations during Ultra-Slow-Roll inflation shows that environmental decoherence erases the interference dip, modifies the growth slope, and induces oscillatory features in the scalar power spectrum and scalar-induced gravitational waves.
Steepest Growth in the Primordial Power Spectrum from Excited States at a Sudden Transition
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abstract
Sudden phase transitions during inflation can give rise to strongly enhanced primordial density perturbations on scales much smaller than those directly probed by cosmic microwave background anisotropies. In this paper, we study the effect of the incoming quantum state on the steepest growth found in the primordial power spectrum using a simple model of an instantaneous transition during single-field inflation. We consider the case of a general de Sitter-invariant initial state for the inflaton field (the $\alpha$-vacuum), and also an incoming state perturbed by a preceding transition. For the $\alpha$-vacua we find that $k^6$ growth is possible for $\alpha>0$, while $k^4$ growth is seen for $\alpha\leq0$, including the standard case of an initial Bunch-Davies vacuum state. The features of an enhanced primordial power spectrum on small scales are thus sensitive to the initial quantum state during inflation. We calculate the scalar-induced gravitational wave power spectrum for each case.
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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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When the Environment Speaks: Quantum Signatures in Non-Attractor Inflation
An open quantum system treatment of curvature perturbations during Ultra-Slow-Roll inflation shows that environmental decoherence erases the interference dip, modifies the growth slope, and induces oscillatory features in the scalar power spectrum and scalar-induced gravitational waves.
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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.