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Dynamical Properties of the Mukhanov-Sasaki Hamiltonian in the Context of Adiabatic Vacua and the Lewis-Riesenfeld Invariant

Institute for Quantum Gravity, Department of Physics, FAU Erlangen-Nürnberg, 91058 Erlangen, Germany
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Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Universe 2019, 5(7), 170; https://doi.org/10.3390/universe5070170
Received: 1 February 2019 / Revised: 1 July 2019 / Accepted: 10 July 2019 / Published: 13 July 2019
(This article belongs to the Special Issue Progress in Group Field Theory and Related Quantum Gravity Formalisms)
We use the method of the Lewis-Riesenfeld invariant to analyze the dynamical properties of the Mukhanov-Sasaki Hamiltonian and, following this approach, investigate whether we can obtain possible candidates for initial states in the context of inflation considering a quasi-de Sitter spacetime. Our main interest lies in the question of to which extent these already well-established methods at the classical and quantum level for finitely many degrees of freedom can be generalized to field theory. As our results show, a straightforward generalization does in general not lead to a unitary operator on Fock space that implements the corresponding time-dependent canonical transformation associated with the Lewis-Riesenfeld invariant. The action of this operator can be rewritten as a time-dependent Bogoliubov transformation, where we also compare our results to already existing ones in the literature. We show that its generalization to Fock space has to be chosen appropriately in order to not violate the Shale-Stinespring condition. Furthermore, our analysis relates the Ermakov differential equation that plays the role of an auxiliary equation, whose solution is necessary to construct the Lewis-Riesenfeld invariant, as well as the corresponding time-dependent canonical transformation, to the defining differential equation for adiabatic vacua. Therefore, a given solution of the Ermakov equation directly yields a full solution of the differential equation for adiabatic vacua involving no truncation at some adiabatic order. As a consequence, we can interpret our result obtained here as a kind of non-squeezed Bunch-Davies mode, where the term non-squeezed refers to a possible residual squeezing that can be involved in the unitary operator for certain choices of the Bogoliubov map. View Full-Text
Keywords: quantum cosmology; cosmological perturbation theory; Lewis-Riesenfeld invariant; Bogoliubov transformation; adiabatic vacua quantum cosmology; cosmological perturbation theory; Lewis-Riesenfeld invariant; Bogoliubov transformation; adiabatic vacua
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Fahn, M.J.; Giesel, K.; Kobler, M. Dynamical Properties of the Mukhanov-Sasaki Hamiltonian in the Context of Adiabatic Vacua and the Lewis-Riesenfeld Invariant. Universe 2019, 5, 170.

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