The physical aspect of a general perturbation theory is explored. Its role as a physical principle for understanding the interaction among the matters with different levels of hierarchy is appreciated. It is shown that the general perturbation theory can not only be used for understanding the various electronic phenomena including the nature of chemical bonds but also serve as a unified theme f...

In this paper we propose a new way of organizing many-body perturbation theory in the Path-integral formulation where a set of quasi-particle wavefunctionals ψ’s are introduced and are identified with quasi-particles in Landau Fermi liquid theory. We show how Fermi liquid theory can be obtained through ψ’s in this new framework of perturbation theory, where the only assumption is adiabaticity b...

An algorithm, based on numerical description of the terms of many-body perturbation theory (Goldstone diagrams), is presented. The algorithm assumes a basis set of orthogonal single-electron orbitals supplied by the user. These orbitals are the eigenstates of the Dirac operator in the spherically-symmetric case. Apart from this the algorithm is practically free from any limitations and can be u...

Energies, transition probabilities, and lifetimes are calculated for 3d states in Ca-like ions with nuclear charges Z ranging from 22 to 100. Relativistic many-body perturbation theory ~MBPT!, including the Breit interaction, is used to evaluate retarded M1 and E2 matrix elements. The calculations start from a 1s2s2p3s3p Dirac-Fock potential. First-order perturbation theory is used to obtain in...

A review is given of our recent application of a systematic microscopic formulation of quantum many-body theory, namely the coupled-cluster method (CCM), to Hamiltonian U (1) lattice gauge models in the pure gauge sector. It is emphasized that our CCM results represent a natural extension or resummation of the results from the strong-coupling perturbation theory.

4 Classical perturbation theory 4 4.1 The classical theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.2 The precession of the perihelion of Mercury . . . . . . . . . . . . . . . . . . . . 6 4.2.1 Delaunay action–angle variables . . . . . . . . . . . . . . . . . . . . . . 6 4.2.2 The restricted, planar, circular, three–body problem . . . . . . . . . . . 7 4.2.3 Expansi...

We compare the nonlinear matter power spectrum in real space calculated analytically from third-order perturbation theory with N-body simulations at 1 < z < 6. We find that the perturbation theory prediction agrees with the simulations to better than 1% accuracy in the weakly nonlinear regime in which the dimensionless power spectrum, (k) 1⁄4 k P(k)/2 , which approximately gives the variance of...