Perturbation theory for the logarithm of a positive operator

Nima Lashkari (School of Natural Sciences, Institute for Advanced Study, Einstein Drive, Princeton, NJ, 08540, USA) ; Hong Liu (Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA) ; Srivatsan Rajagopal (Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA)

In various contexts in mathematical physics, such as out-of-equilibrium physics and the asymptotic information theory of many-body quantum systems, one needs to compute the logarithm of a positive unbounded operator. Examples include the von Neumann entropy of a density matrix and the flow of operators with the modular Hamiltonian in the Tomita-Takesaki theory. Often, one encounters the situation where the operator under consideration, which we denote by ∆, can be related by a perturbative series to another operator ∆0, whose logarithm is known. We set up a perturbation theory for the logarithm log ∆. It turns out that the terms in the series possess a remarkable algebraic structure, which enables us to write them in the form of nested commutators plus some “contact terms”.

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      "surname": "Rajagopal", 
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  "abstracts": [
    {
      "source": "Springer", 
      "value": "In various contexts in mathematical physics, such as out-of-equilibrium physics and the asymptotic information theory of many-body quantum systems, one needs to compute the logarithm of a positive unbounded operator. Examples include the von Neumann entropy of a density matrix and the flow of operators with the modular Hamiltonian in the Tomita-Takesaki theory. Often, one encounters the situation where the operator under consideration, which we denote by \u2206, can be related by a perturbative series to another operator \u22060, whose logarithm is known. We set up a perturbation theory for the logarithm log \u2206. It turns out that the terms in the series possess a remarkable algebraic structure, which enables us to write them in the form of nested commutators plus some \u201ccontact terms\u201d."
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Published on:
16 November 2023
Publisher:
Springer
Published in:
Journal of High Energy Physics , Volume 2023 (2023)
Issue 11
Pages 1-24
DOI:
https://doi.org/10.1007/JHEP11(2023)097
arXiv:
1811.05619
Copyrights:
The Author(s)
Licence:
CC-BY-4.0

Fulltext files: