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Quenched coupling and thermal behavior in the O(N) vector model
Stockholm University, Faculty of Science, Department of Physics.
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Thermalization is an elusive phenomenon in quantum mechanics. Since according to the AdS/CFT correspondence, a thermal state in the boundary CFT is dual to a black hole in the bulk spacetime, thermalization in the CFT is dual to black hole formation in AdS. Thus, understanding quantum thermalization is likely a key component in understanding the information paradox---the contradiction between QFT and general relativity occurring when a black hole seemingly erases the information of whatever went into creating it.

(Apparent) thermalization in QFT can be investigated by imposing a quench, i.e., a sudden change of some parameter of the theory, and subsequently studying the equilibration process. In this thesis we aim to gain understanding of quantum thermalization by investigating the late-time quench dynamics of a simple free field theory, namely the $O(N)$ vector model. Since the theory is integrable, ``true'' thermalization will not occur but an approximate thermalization. We use different probes such as the effective density matrix and the spectral density function to investigate the extent to which the (pure) state ``looks'' thermal and how this deviates from conventional thermality.

Place, publisher, year, edition, pages
Stockholm University, 2019.
National Category
Other Physics Topics
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-168940OAI: oai:DiVA.org:su-168940DiVA, id: diva2:1316419
Available from: 2019-06-11 Created: 2019-05-17 Last updated: 2019-12-13Bibliographically approved
List of papers
1. Quenched coupling, entangled equilibria, and correlated composite operators: a tale of two O(N) models
Open this publication in new window or tab >>Quenched coupling, entangled equilibria, and correlated composite operators: a tale of two O(N) models
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2019 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 8, article id 139Article in journal (Refereed) Published
Abstract [en]

A macroscopic version of Einstein-Podolsky-Rosen entanglement is obtained by quenching a quadratic coupling between two O(N) vector models. A quench of the mixed vacuum produces an excited entangled state, reminiscent of purified thermal equilibrium, whose properties can be studied analytically in the free limit of the individual field theories. The decoupling of different wavelength modes in free field theory prevents true thermalisation but a more subtle difference is that the density operator obtained by a partial trace does not commute with the post-quench Hamiltonian. Generalized thermal behaviour is obtained at late times, in the limit of weak initial mixing or a smooth but rapid quench. More surprisingly, late-time correlation functions of composite operators in the post-quench free field theory share interesting properties with correlators in strongly coupled systems. We propose a holographic interpretation of our result.

Keywords
AdS-CFT Correspondence, Effective Field Theories, Holography and condensed matter physics (AdS/CMT)
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-175109 (URN)10.1007/JHEP08(2019)139 (DOI)000483943900002 ()
Available from: 2019-10-18 Created: 2019-10-18 Last updated: 2019-12-13Bibliographically approved

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