A1 Journal article (refereed)
Non-equilibrium dynamics of a scalar field with quantum backreaction (2021)

Kainulainen, K., & Koskivaara, O. (2021). Non-equilibrium dynamics of a scalar field with quantum backreaction. Journal of High Energy Physics, 2021(12), Article 190. https://doi.org/10.1007/jhep12(2021)190

JYU authors or editors

Publication details

All authors or editors: Kainulainen, Kimmo; Koskivaara, Olli

Journal or series: Journal of High Energy Physics

ISSN: 1126-6708

eISSN: 1029-8479

Publication year: 2021

Volume: 2021

Issue number: 12

Article number: 190

Publisher: Springer

Publication country: Germany

Publication language: English

DOI: https://doi.org/10.1007/jhep12(2021)190

Publication open access: Openly available

Publication channel open access: Open Access channel

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/79284

Web address of parallel published publication (pre-print): https://arxiv.org/abs/2105.09598


We study the dynamical evolution of coupled one- and two-point functions of a scalar field in the 2PI framework at the Hartree approximation, including backreaction from out-of-equilibrium modes. We renormalize the 2PI equations of motion in an on-shell scheme in terms of physical parameters. We present the Hartree-resummed renormalized effective potential at finite temperature and critically discuss the role of the effective potential in a non-equilibrium system. We follow the decay and thermalization of a scalar field from an initial cold state with all energy stored in the potential, into a fully thermalized system with a finite temperature. We identify the non-perturbative processes of parametric resonance and spinodal instability taking place during the reheating stage. In particular we study the unstable modes in the region where the vacuum 1PI effective action becomes complex and show that such spinodal modes can have a dramatic effect on the evolution of the one-point function. Our methods can be easily adapted to simulate reheating at the end of inflation.

Keywords: particle physics; cosmology; quantum field theory

Free keywords: nonperturbative effects; thermal field theory; quantum dissipative systems

Contributing organizations

Related projects

  • Dark Universe
      • Kainulainen, Kimmo
    • Academy of Finland

Ministry reporting: Yes

Reporting Year: 2021

JUFO rating: 2

Last updated on 2022-20-09 at 14:25