The paper "Cosmic Purity Lost: Perturbative and Resummed Late-Time Inflationary Decoherence" by C.P. Burgess et al. investigates the decoherence of unobserved fields in the context of inflationary cosmology. The authors compute the rate at which these fields decohere other fields they couple to, both in flat space and de Sitter space, for scalar fields prepared in their standard adiabatic vacuum. They find that decoherence is very efficient in de Sitter space once the modes involved pass outside the Hubble scale, leading to secular growth that indicates the breakdown of perturbative methods on a timescale much longer than the Hubble time. The authors develop a method to match the perturbative evolution at early times onto a late-time Lindblad evolution, allowing for a reliable resummation of the perturbative result beyond the perturbative regime. They show that super-Hubble modes are predominantly decohered by unobserved modes that are also super-Hubble. When applied to curvature perturbations during inflation, this observation closes a potential loophole in recent calculations of the late-time purity of observable primordial fluctuations. The paper also explores the implications of these findings for late-time predictions and the evolution of decoherence, providing a detailed analysis of the system's purity and its evolution equation.The paper "Cosmic Purity Lost: Perturbative and Resummed Late-Time Inflationary Decoherence" by C.P. Burgess et al. investigates the decoherence of unobserved fields in the context of inflationary cosmology. The authors compute the rate at which these fields decohere other fields they couple to, both in flat space and de Sitter space, for scalar fields prepared in their standard adiabatic vacuum. They find that decoherence is very efficient in de Sitter space once the modes involved pass outside the Hubble scale, leading to secular growth that indicates the breakdown of perturbative methods on a timescale much longer than the Hubble time. The authors develop a method to match the perturbative evolution at early times onto a late-time Lindblad evolution, allowing for a reliable resummation of the perturbative result beyond the perturbative regime. They show that super-Hubble modes are predominantly decohered by unobserved modes that are also super-Hubble. When applied to curvature perturbations during inflation, this observation closes a potential loophole in recent calculations of the late-time purity of observable primordial fluctuations. The paper also explores the implications of these findings for late-time predictions and the evolution of decoherence, providing a detailed analysis of the system's purity and its evolution equation.