[THREAD] Very thrilled to share our first collaboration with Vincent Vennin @APC_Laboratory and Julien Grain @IASorsay realized at @UnivParisSaclay and @Univ_Paris on #quantum field theory in curved space and #QuantumCosmology. (1/8) arxiv.org/abs/2104.14942

In this paper, we derive the quantum state in which are placed two linearly interacting scalar fields in a homogeneous and isotropic universe. (2/8)

In this setting, the dynamics is described by mathematical objects that are elements of the Lie group Sp(4,R). We first investigate its mathematical structure, which allows us to derive the exact quantum state of the system: a four-mode squeezed state. (3/8)

This quantum state can be understood as two single fields exchanging quanta. In the case where the two fields are weakly coupled, performing an expansion at nth order in the interaction coupling is equivalent look for the exchange of nth particles. (4/8)

We also derive the phase-space representation of the system which is given by the Wigner function. The state being Gaussian, this representation can be more efficient to perform computations. (5/8)

Finally, we discuss environmental effects in the case where one of the two fields is unobserved. There is always a range of interaction coupling for which decoherence occurs without substantially affecting the observables of the system. (6/8)

In the future, we plan to apply the tools developed in this paper to investigate situations of cosmological interest such as adiabatic and isocurvature perturbations in multifield inflation. (7/8)