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This paper gives an introduction to the Keldysh formalism, with emphasis on its usefulness in time-dependent density functional theory. In the first part we introduce the Keldysh contour and the one-particle Green function defined on this…

Mesoscale and Nanoscale Physics · Physics 2007-05-23 Robert van Leeuwen , Nils Erik Dahlen , Gianluca Stefanucci , Carl-Olof Almbladh , Ulf von Barth

The theoretical investigation of charge (and spin) transport at nanometer length scales requires the use of advanced and powerful techniques able to deal with the dynamical properties of the relevant physical systems, to explicitly include…

Mesoscale and Nanoscale Physics · Physics 2015-05-13 D. A. Ryndyk , R. Gutierrez , B. Song , G. Cuniberti

I review the way the many-body Green functions are used to renormalize the perturbation theory of correlated fermions. The Green functions are introduced to implement systematically dynamical corrections to the static mean-field theory. The…

Strongly Correlated Electrons · Physics 2021-09-21 Václav Janiš

We extend the concept of the functional renormalization for quantum many-body problems to non-equilibrium situations. Using a suitable generating functional based on the Keldysh approach, we derive a system of coupled differential equations…

Strongly Correlated Electrons · Physics 2013-05-29 R. Gezzi , Th. Pruschke , V. Meden

Bosonization technique for one-dimensional fermions out of equilibrium is developed in the framework of the Keldysh action formalism. We first demonstrate how this approach is implemented for free fermions and for the problem of…

Mesoscale and Nanoscale Physics · Physics 2010-02-25 D. B. Gutman , Yuval Gefen , A. D. Mirlin

We present a quantum kinetic approach for the time-resolved description of many-body effects in photoionization processes in atoms. The method is based on the non-equilibrium Green functions formalism and solves the Keldysh/Kadanoff-Baym…

Atomic Physics · Physics 2015-05-13 D. Hochstuhl , K. Balzer , S. Bauch , M. Bonitz

The theory of real-time quantum many-body dynamics as put forward in Ref. [arXiv:0710.4627] is evaluated in detail. The formulation is based on a generating functional of correlation functions where the Keldysh contour is closed at a given…

Quantum Gases · Physics 2011-02-09 Thomas Gasenzer , Stefan Kessler , Jan M. Pawlowski

We construct a nonperturbative nonequilibrium theory for graphene electrons interacting via the instantaneous Coulomb interaction by combining the functional renormalization group method with the nonequilibrium Keldysh formalism. The…

Mesoscale and Nanoscale Physics · Physics 2017-03-15 Christian Fräßdorf , Johannes E. M. Mosig

Schwinger Keldysh field theory is a widely used paradigm to study non-equilibrium dynamics of quantum many-body systems starting from a thermal state. We extend this formalism to describe non-equilibrium dynamics of quantum systems starting…

Statistical Mechanics · Physics 2019-03-13 Ahana Chakraborty , Pranay Gorantla , Rajdeep Sensarma

We present a comprehensive pedagogical discussion of a family of models describing the propagation of a single particle in a multicomponent non-Markovian Gaussian random field. We report some exact results for single-particle Green's…

Mesoscale and Nanoscale Physics · Physics 2026-01-29 D. V. Efremov , M. N. Kiselev

Motivated by cosmological Hartle-Hawking and microcanonical density matrix prescriptions for the quantum state of the Universe we develop Schwinger-Keldysh in-in formalism for generic nonequilibrium dynamical systems with the initial…

High Energy Physics - Theory · Physics 2023-09-08 Andrei O. Barvinsky , Nikita Kolganov

We study the 4-point function in the Keldysh formalism of the closed time path formulation of real time finite temperature field theory. We derive the KMS conditions for these functions and discuss the number of 4-point functions that are…

High Energy Physics - Phenomenology · Physics 2016-09-06 M. E. Carrington , Hou Defu , J. C. Sowiak

We derive equations of motion for higher order density response functions using the theory of thermodynamic Green's functions. We also derive expressions for the higher order generalized dielectric functions and polarization functions.…

Strongly Correlated Electrons · Physics 2024-10-04 Jan Vorberger , Tobias Dornheim , Maximilian P. Böhme , Zhandos Moldabekov , Panagiotis Tolias

Different non-equilibrium situations have recently been considered when studying the thermal Casimir--Polder interaction with a body. We show that the Keldysh Green function method provides a very general common framework for such studies…

Quantum Physics · Physics 2017-08-23 Simen Å. Ellingsen , Yury Sherkunov , Stefan Y. Buhmann , Stefan Scheel

The infrared regime of fermionic Green and vertex functions is studied analytically within a geometric approach which simulates soft interactions by an {\it effective} theory of contours. Expanding the particle path integral in terms of…

High Energy Physics - Theory · Physics 2007-05-23 N. G. Stefanis

We introduce a method to evaluate the steady-state non-equilibrium Keldysh-Schwinger Green's functions for infinite systems subject to both an electric field and a coupling to reservoirs. The method we present exploits a physical…

Strongly Correlated Electrons · Physics 2020-08-26 Christian Klöckner , Dante Marvin Kennes , Christoph Karrasch

Nonequilibrium quantum mechanics can be solved with the Keldysh formalism, which evolves the quantum mechanical states forward in time in the presence of a time-dependent field, and then evolves them backward in time, undoing the effect of…

Strongly Correlated Electrons · Physics 2007-05-23 J. K. Freericks , V. Turkowski , V. Zlatic

We apply the Keldysh formalism in order to derive a current formula easy to use for a system with many sites, one of which is interacting. The main technical challenge is to deal with the lesser Green function. It turns out that, in the…

Mesoscale and Nanoscale Physics · Physics 2009-11-13 I. V. Dinu , M. Tolea , A. Aldea

We describe microscopic theory for the quantum transport through finite interacting systems connected to noninteracting leads. It can be applied to small systems such as quantum dots, quantum wires, atomic chain, molecule, and so forth. The…

Mesoscale and Nanoscale Physics · Physics 2007-05-23 Akira Oguri

Lectures notes for 2004 Les Houches Summer School on "Nanoscopic Quantum Transport". These lectures contain an introduction to Keldysh formalism for interacting bosonic and fermionic systems, presented in the functional integral framework.…

Disordered Systems and Neural Networks · Physics 2007-05-23 Alex Kamenev
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