The Semiclassical Einstein-Klein-Gordon System: Asymptotic Analysis of Minkowski Spacetime

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Main Authors: Galanda, Stefano, Meda, Paolo, Murro, Simone, Pinamonti, Nicola, Schmid, Gabriel
Format: Preprint
Published: 2026
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author Galanda, Stefano
Meda, Paolo
Murro, Simone
Pinamonti, Nicola
Schmid, Gabriel
author_facet Galanda, Stefano
Meda, Paolo
Murro, Simone
Pinamonti, Nicola
Schmid, Gabriel
contents We establish the linear instability of the semiclassical Einstein-Klein-Gordon system linearised about the Minkowski vacuum spacetime. The proof relies on formulating a forcing problem for both metric and state perturbations within the space of past-compact sections. This geometric framework admits a unique tensor decomposition which, in conjunction with the quantum Møller operator, enables the decoupling of the linearised system into two distinct Cauchy problems. Consequently, the metric perturbations are shown to be governed by a higher-order, nonlocal hyperbolic partial differential equation. By relegating the nonlocal contributions to subleading order, we establish the well-posedness of this forcing problem. Furthermore, we provide a rigorous asymptotic analysis for physically admissible choices of the renormalisation constants. We prove that the system exhibits a late-time linear instability: the metric perturbations grow exponentially, bounded strictly by a universal scale H, thereby indicating a quantum backreaction-driven transition toward a de Sitter cosmological spacetime. Provided the parameters governing the system are restricted to a physically relevant regime, this universal scale is compatible with the measured expansion of our universe.
format Preprint
id arxiv_https___arxiv_org_abs_2604_01047
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle The Semiclassical Einstein-Klein-Gordon System: Asymptotic Analysis of Minkowski Spacetime
Galanda, Stefano
Meda, Paolo
Murro, Simone
Pinamonti, Nicola
Schmid, Gabriel
Mathematical Physics
General Relativity and Quantum Cosmology
Analysis of PDEs
Differential Geometry
Primary: 83C05, 83C47, Secondary: 35L25, 81T20
We establish the linear instability of the semiclassical Einstein-Klein-Gordon system linearised about the Minkowski vacuum spacetime. The proof relies on formulating a forcing problem for both metric and state perturbations within the space of past-compact sections. This geometric framework admits a unique tensor decomposition which, in conjunction with the quantum Møller operator, enables the decoupling of the linearised system into two distinct Cauchy problems. Consequently, the metric perturbations are shown to be governed by a higher-order, nonlocal hyperbolic partial differential equation. By relegating the nonlocal contributions to subleading order, we establish the well-posedness of this forcing problem. Furthermore, we provide a rigorous asymptotic analysis for physically admissible choices of the renormalisation constants. We prove that the system exhibits a late-time linear instability: the metric perturbations grow exponentially, bounded strictly by a universal scale H, thereby indicating a quantum backreaction-driven transition toward a de Sitter cosmological spacetime. Provided the parameters governing the system are restricted to a physically relevant regime, this universal scale is compatible with the measured expansion of our universe.
title The Semiclassical Einstein-Klein-Gordon System: Asymptotic Analysis of Minkowski Spacetime
topic Mathematical Physics
General Relativity and Quantum Cosmology
Analysis of PDEs
Differential Geometry
Primary: 83C05, 83C47, Secondary: 35L25, 81T20
url https://arxiv.org/abs/2604.01047