Classical entanglement structure in the wavefunction of inflationary fluctuations

Abstract

The emergence of preferred classical variables within a many-body wavefunction is encoded in its entanglement structure in the form of redundant classical information shared between many spatially local subsystems. We show how such structure can be generated via cosmological dynamics from the vacuum state of a massless field, causing the wavefunction to branch into classical field configurations on large scales. An accelerating epoch first excites the vacuum into a superposition of classical fields as well as a highly sensitive bath of squeezed super-horizon modes. During a subsequent decelerating epoch, gravitational interactions allow these modes to collect information about longer-wavelength fluctuations. This information disperses spatially, creating long-range redundant correlations in the wavefunction. The resulting classical observables, preferred basis for decoherence, and system/environment decomposition emerge from the translation invariant wavefunction and Hamiltonian, rather than being fixed by hand. We discuss the role of squeezing, the cosmological horizon scale, and phase information in the wavefunction, as well as aspects of wavefunction branching for continuous variables and in field theories.

Entropy production in inflation from spectator loops

“…This means that, before one makes any definite conclusion concerning the strength of decoherence during inflation, one also ought to investigate the effect of the quantum gravitational loops. In fact, there have been several attempts to do precisely that [26,27,30,31,47]. In addition, a lot of work has been invested into a much easier set of problems, namely into studying how the inflaton coupling with the other quantum fields (scalar, fermionic or vector) induces decoherence in the inflaton sector [16,18,31,34].…”

“…While early works [11][12][13][14][15][16][17][18] used the late time observer's inability to get a complete access to the state of cosmological perturbations as the principal source of decoherence and classicalization (the so-called 'decoherence without decoherence'), later works used more realistic settings, in which (dissipative) interactions among quantum fields during (or after) inflation is the principal cause for decoherence. The interactions considered range from self-interactions of the inflaton field [24][25][26][27], interactions with gravitational waves [28,29], interactions with other scalar fields [30][31][32][33], as well as interactions with massive fermionic fields [34].…”

Naturalness, Wilsonian renormalization, and “fundamental parameters” in quantum field theory

“…A rigorous mathematical definition of a QFT (including an EFT) is widely understood to require specification of the theory's Hilbert space and unitary time evolution via some Hamiltonian. Such a definition permits application of the theory outside of the restricted context of scattering experiments, as required for example in the context of quantum cosmology (see, e.g., (Nelson and Riedel, 2017)). How are the Hilbert space and Hamiltonian of an EFT specified on the approach just described, in which all points along the RG trajectory constitute physically equivalent parametrizations of observables and physical amplitudes?…”

Decoherence and entropy generation at one loop in the inflationary de Sitter spacetime for Yukawa interaction

“…The present study is similar to the recent one made in [66], which considered the same theory in the Minkowski spacetime. Previous literature has considered various types of interactions, such as self-interactions of the inflaton field [67][68][69][70], interactions with gravitational waves [71,72], interactions with the system scalar with another scalar [73][74][75][76], as well as interactions with massless and massive fermionic fields [77][78][79][80][81]. We also refer our reader to [82][83][84][85] for some earlier analysis on open quantum systems with scalars and fermions and [86,87] for the analytical aspects of correlators…”