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dc.contributor.authorHyrkäs, Markku
dc.contributor.authorKarlsson, Daniel
dc.contributor.authorvan Leeuwen, Robert
dc.date.accessioned2022-08-25T05:29:24Z
dc.date.available2022-08-25T05:29:24Z
dc.date.issued2022
dc.identifier.citationHyrkäs, M., Karlsson, D., & van Leeuwen, R. (2022). Cutting rules and positivity in finite temperature many-body theory. <i>Journal of Physics A : Mathematical and Theoretical</i>, <i>55</i>(33), Article 335301. <a href="https://doi.org/10.1088/1751-8121/ac802d" target="_blank">https://doi.org/10.1088/1751-8121/ac802d</a>
dc.identifier.otherCONVID_148946372
dc.identifier.urihttps://jyx.jyu.fi/handle/123456789/82804
dc.description.abstractFor a given diagrammatic approximation in many-body perturbation theory it is not guaranteed that positive observables, such as the density or the spectral function, retain their positivity. For zero-temperature systems we developed a method [Phys.Rev.B{\bf 90},115134 (2014)] based on so-called cutting rules for Feynman diagrams that enforces these properties diagrammatically, thus solving the problem of negative spectral densities observed for various vertex approximations. In this work we extend this method to systems at finite temperature by formulating the cutting rules in terms of retarded $N$-point functions, thereby simplifying earlier approaches and simultaneously solving the issue of non-vanishing vacuum diagrams that has plagued finite temperature expansions. Our approach is moreover valid for nonequilibrium systems in initial equilibrium and allows us to show that important commonly used approximations, namely the $GW$, second Born and $T$-matrix approximation, retain positive spectral functions at finite temperature. Finally we derive an analytic continuation relation between the spectral forms of retarded $N$-point functions and their Matsubara counterparts and a set of Feynman rules to evaluate them.en
dc.format.mimetypeapplication/pdf
dc.language.isoeng
dc.publisherIOP Publishing
dc.relation.ispartofseriesJournal of Physics A : Mathematical and Theoretical
dc.rightsIn Copyright
dc.subject.otherdiagrammatic perturbation theory
dc.subject.othernon-equilibrium Green’s functions
dc.subject.otherquantum many-body theory
dc.subject.otherspectral properties
dc.titleCutting rules and positivity in finite temperature many-body theory
dc.typearticle
dc.identifier.urnURN:NBN:fi:jyu-202208254337
dc.contributor.laitosFysiikan laitosfi
dc.contributor.laitosDepartment of Physicsen
dc.contributor.oppiaineNanoscience Centerfi
dc.contributor.oppiaineNanoscience Centeren
dc.type.urihttp://purl.org/eprint/type/JournalArticle
dc.type.coarhttp://purl.org/coar/resource_type/c_2df8fbb1
dc.description.reviewstatuspeerReviewed
dc.relation.issn1751-8113
dc.relation.numberinseries33
dc.relation.volume55
dc.type.versionacceptedVersion
dc.rights.copyright© 2022 IOP Publishing Ltd
dc.rights.accesslevelopenAccessfi
dc.relation.grantnumber308697
dc.relation.grantnumber317139
dc.format.contentfulltext
dc.rights.urlhttp://rightsstatements.org/page/InC/1.0/?language=en
dc.relation.doi10.1088/1751-8121/ac802d
dc.relation.funderResearch Council of Finlanden
dc.relation.funderResearch Council of Finlanden
dc.relation.funderSuomen Akatemiafi
dc.relation.funderSuomen Akatemiafi
jyx.fundingprogramPostdoctoral Researcher, AoFen
jyx.fundingprogramAcademy Project, AoFen
jyx.fundingprogramTutkijatohtori, SAfi
jyx.fundingprogramAkatemiahanke, SAfi
jyx.fundinginformationD.K. acknowledges the academy of Finland for funding under Project No. 308697. M.H. thanks the Finnish Cultural Foundation for support. R.v.L. acknowledges the academy of Finland for funding under Project No. 317139
dc.type.okmA1


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