# Nonthermal fixed points in quantum field theory beyond the weak-coupling limit

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Publication Date: 2017-02-22

Journal Title: Physical Review D - Particles, Fields, Gravitation and Cosmology

Publisher: American Physical Society

Volume: 95

Number: 036016

Language: English

Type: Article

This Version: AM

Citation: Berges, J., & Wallisch, B. (2017). Nonthermal fixed points in quantum field theory beyond the weak-coupling limit. Physical Review D - Particles, Fields, Gravitation and Cosmology, 95 (036016)https://doi.org/10.1103/PhysRevD.95.036016

Abstract: Quantum systems in extreme conditions can exhibit universal behavior far from equilibrium associated to nonthermal fixed points with a wide range of topical applications from early-Universe inflaton dynamics and heavy-ion collisions to strong quenches in ultracold quantum gases. So far, most studies have relied on a mapping of the quantum dynamics onto a classical-statistical theory that can be simulated on a computer. However, the mapping is based on a weak-coupling limit, while phenomenological applications often require moderate interaction strengths. We report on the observation of nonthermal fixed points directly in quantum field theory beyond the weak-coupling limit. For the example of a relativistic scalar O($\textit{N}$)-symmetric quantum field theory, we numerically solve the nonequilibrium dynamics employing a 1/$\textit{N}$ expansion to next-to-leading order, which does not rely on a small coupling parameter. Starting from two different sets of overoccupied and of strong-field initial conditions, we find that nonthermal fixed points are not restricted to parameter ranges suitable for classical-statistical simulations but extend also to couplings of order 1. While the infrared behavior is found to be insensitive to the differences in the initial conditions, we demonstrate that transport phenomena to higher momenta depend on the presence or absence of a symmetry-breaking field expectation value.

Sponsorship: B. W. gratefully acknowledges support from the Studienstiftung des deutschen Volkes, a Starting Grant of the European Research Council (Grant No. 279617), a Cambridge European Scholarship of the Cambridge Trust, and a Science and Technology Facilities Council (STFC) Studentship. Parts of this work were performed on the computational resource bwUniCluster funded by the Ministry of Science, Research and the Arts Baden-Württemberg and the Universities of the State of Baden-Württemberg, Germany, within the framework program bwHPC. This work is part of and supported by the Deutsche Forschungsgemeinschaft (DFG) Collaborative Research Centre “SFB 1225 (ISOQUANT).

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External DOI: https://doi.org/10.1103/PhysRevD.95.036016

This record's URL: https://www.repository.cam.ac.uk/handle/1810/263229

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Autor: Berges, J Wallisch, Benjamin

Fuente: https://www.repository.cam.ac.uk/handle/1810/263229

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