Cosmic decoherence: massive fields

Abstract

We study the decoherence of massive fields during inflation based on the Zurek's density matrix approach. With the cubic interaction between inflaton and massive fields, the reduced density matrix for the massive fields can be calculated in the Schrödinger picture which is related to the variance of the non-Gaussian exponent in the wave functional. The decoherence rate is computed in the one-loop form from functional integration. For heavy fields with m O(H), quantum fluctuations will easily stay in the quantum state and decoherence is unlikely. While for light fields with mass smaller than O(H), quantum fluctuations are easily decohered within 5 ∼ 10 e-folds after Hubble crossing. Thus heavy fields can play a key role in studying problems involving inflationary quantum information.

Non-Gaussianity as a particle detector

“…At subleading orders, however, there are non-zero contributions from odd-spin particles. 18 When conformal 17 Potential tests of the quantum nature of cosmological fluctuations have also been discussed in [50][51][52][53][54]. 18 When the approximate conformal invariance is valid, we can think of this in terms of correlation functions of the inflaton Φ(t, x) = φ(t) + ϕ(t, x), whereφ = 0 characterizes the weak breaking of conformal symmetry.…”

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].…”

“…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 the earlier works considered simple models with bilinear couplings [16,18] (since these couplings are non-dissipative, they are not true interactions), more recent works studied true interactions [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].…”

On the effective field theory for quasi-single field inflation

“…Thus they are not ideal for studying the quantum nature in the primordial universe, such as entanglements, Bell inequalities, etc. Massive fields have slowly increasing or non-increasing particle number and thus provide a cleaner arena to study the quantum effects of the primordial universe [38].…”