Many-body diagrammatic expansion in a kohn-sham basis: implications for time-dependent density functional theory of excited states

We formulate diagrammatic rules for many-body perturbation theory which uses Kohn-Sham Green's functions as basic propagators. The diagram technique allows one to study the properties of the dynamic nonlocal exchange-correlation (xc) kernel f(xc). We show that the spatial nonlocality of f(xc) is strongly frequency dependent. In particular, in extended systems the nonlocality range diverges at the excitation energies. This divergency is related to the discontinuity of the xc potential.     

Exact treatment of exciton-polaron formation by diagrammatic Monte Carlo simulations

We develop an approximation-free diagrammatic Monte Carlo technique to study fermionic particles interacting with each other simultaneously through both an attractive Coulomb potential and bosonic excitations of the underlying medium. Exemplarily we apply the method to the long-standing exciton-polaron problem and present numerically exact results for the wave function, ground-state energy, binding energy and effective mass of this quasiparticle. Focusing on the electron-hole pair bound-state formation, we discuss various limiting cases of a generic exciton-polaron model. The frequently used instantaneous approximation to the retarded interaction due to the exchange of phonons is found to be of very limited applicability.     

Many-body theory of nuclear matter

We combine the many-body theory and the low-density expansion developed by Brueckner, Bethe and others to investigate several properties of the ground state and of single-particle excited states of symmetric nuclear matter. We calculate the following quantities from Reid's hard core nucleon-nucleon interaction: strength, energy-dependence, nonlocality and density-dependence of the real and of the imaginary parts of the optical-model potential, momentum distribution in the interacting ground state, dependence on density and momentum of the norm of a quasiparticle and of the effective mass, spectral function for particle states, saturation density and average binding energy per nucleon. No free parameter is adjusted in the calculation; good agreement is obtained with empirical values. It is shown that the effective mass has a narrow maximum at the Fermi surface; this is investigated in the framework of analytical models.     

Many-body effects in nuclei

A correction to nuclear structure calculations due to the finite lifetime of the excited states of a nucleus entails many-body effects of different nature. The analytical structure, as well as the results of numerical calculations, are given and discussed.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Many-body calculation of hyperfine structure

The many-body perturbation theory of Brueckner and Goldstone is used to calculated the hyperfine contact interaction of oxygen. The calculated value for |ψ(0)|² is 0.0601.     

A diagrammatic approach to spin algebras

A reduction formula for the thermal average of the time-ordered product of spin operators for a magnetic moment in a field H is presented. The reduction formula and the spin algebra are used to compute the magnetization. The procedure provides the basis for a diagrammatic approach to interacting spin systems.     

A diagrammatic categorification of the fermion algebra

In this paper, we study the diagrammatic categorification of the fermion algebra. We construct a graphical category corresponding to the one-dimensional （1D） fermion algebra, and we investigate the properties of this category. The categorical analogues of the Fock states are some kind of 1-morphisms in our category, and the dimension of the vector space of 2-morphisms is exactly the inner product of the corresponding Fock states. All the results in our categorical framework coincide exnetlv with those in normal quantum mechanics.     

Many-body approximation scheme beyond GW

We explore the combination of the extended dynamical mean field theory (EDMFT) with the GW approximation (GWA); the former sums the local contributions to the self-energies to infinite order in closed form and the latter handles the nonlocal ones to lowest order. We investigate the different levels of self-consistency that can be implemented within this method by comparing to the exact quantum Monte Carlo solution of a finite-size model Hamiltonian. We find that using the EDMFT solution for the local self-energies as input to the GWA for the nonlocal self-energies gives the best result.     

Many-body radiative heat transfer theory

In this Letter, an N-body theory for the radiative heat exchange in thermally nonequilibrated discrete systems of finite size objects is presented. We report strong exaltation effects of heat flux which can be explained only by taking into account the presence of many-body interactions. Our theory extends the standard Polder and van Hove stochastic formalism used to evaluate heat exchanges between two objects isolated from their environment to a collection of objects in mutual interaction. It gives a natural theoretical framework to investigate the photon heat transport properties of complex systems at the mesoscopic scale.     

Many-body effects in molecular solids

The effects of many-body interactions in the molecular (rare-gas) solids have been investigated, on the basis of Axilrod-Teller approximation, by a rigid-atom model. It is found that the 3-body interaction is the most dominant of all and the rest may be safely ignored. The discrepancy seen in the phonon dispersion curves is expected to be removed by the inclusion of appropriate anharmonic effects.     

Many-body electronic structure of americium metal

We report computer based simulations of energetics, spectroscopy, and electron-phonon interaction of americium using a novel spectral density functional method. This approach gives rise to a new concept of a many-body electronic structure and reveals the unexpected mixed valence regime of Am 5f6 electrons which under pressure acquire the 5f7 valence state. This explains the unique properties of Am and addresses the fundamental issue of how the localization delocalization edge is approached from the localized side in a closed shell system.     

Many-body aspects of coherent atom-molecule oscillations

We study the many-body effects on coherent atom-molecule oscillations by means of an effective quantum field theory that describes Feshbach-resonant interactions in Bose gases in terms of an atom-molecule Hamiltonian. We determine numerically the many-body corrections to the oscillation frequency for various densities of the atomic condensate. We also derive an analytic expression that approximately describes both the density and magnetic-field dependence of this frequency near the resonance. We find excellent agreement with experiment.     

Many-body effects in diffusion-limited kinetics

We review a novel approach to treating many-body effects in diffusion-limited kinetics. The derivation of the general expression for the survival probability of a Brownian particle in the presence of randomly distributed traps is given. The reduction of this expression to both the Smoluchowski solultion and the wellknown asymptotic behavior is demonstrated. It is shown that the Smoluchowski solution gives a lower bound for the particle survival probability. The correction to the Smoluchowski solution which takes into account the particle death slowdown in the initial process stage is described. The steady-state rate-constant concentration dependence and the reflection of many-body effects in it are discussed in detail.     

Many-body effects in nuclear structure

We calculate, for the first time, the state-dependent pairing gap of a finite nucleus (¹²⁰Sn) diagonalizing the bare nucleon-nucleon potential (Argonne v ₁₄) in a Hartree-Fock basis (with effective k-mass ), within the framework of the generalized Bogoliubov-Valatin approximation including scattering states up to 800 MeV above the Fermi energy to achieve convergence. The resulting gap accounts for about half of the experimental gap. The combined effect of the bare nucleon-nucleon potential and of the induced pairing interaction arising from the exchange of low-lying surface vibrations between nucleons moving in time-reversal states close to the Fermi energy accounts for the experimental gap.Received: 3 November 2003, Published online: 6 July 2004PACS: 21.30.Fe Forces in hadronic systems and effective interactions - 21.60.Jz Hartree-Fock and random-phase approximations - 21.60.-n Nuclear structure models and methods - 27.60. + j      

Regularization of diagrammatic series with zero convergence radius

The divergence of perturbative expansions which occurs for the vast majority of macroscopic systems and follows from Dyson's collapse argument prevents the direct use of Feynman's diagrammatic technique for controllable studies of strongly interacting systems. We show how the problem of divergence can be solved by replacing the original model with a convergent sequence of successive approximations which have a convergent perturbative series while maintaining the diagrammatic structure. As an instructive model, we consider the zero-dimensional |ψ|? theory.