Density and current response functions in strongly disordered electron systems: Diffusion, electrical conductivity and Einstein relation

We study consequences of gauge invariance and charge conservation of an electron gas in a strong random potential perturbed by a weak electromagnetic field. We use quantum equations of motion and Ward identities for one- and two-particle averaged Green functions to establish exact relations between density and current response functions. In particular we find precise conditions under which we can extract the current-current correlation function from the density-density correlation function and vice versa. We use these results in two different ways to extend validity of a formula associating the density response function with the electrical conductivity from semiclassical equilibrium to quantum nonequilibrium systems. Finally we introduce quantum diffusion via a response relating the current with the negative gradient of the charge density. With the aid of this response function we derive a quantum version of the Einstein relation and prove the existence of the diffusion pole in the zero-temperature electron-hole correlation function with the the long-range spatial fluctuations controlled by the static diffusion constant.Comment: 16 pages, REVTeX4, 6 EPS figure

Quantifying the effectiveness of silver ring splints to correct swan-neck deformity

Swan-neck deformity is a common symptom of rheumatoid arthritis affecting the fingers. It can be classified by hyperextension of the proximal interphalangeal (PIP) joint and flexion of the distal interphalangeal joint [1]. Methods to correct hyperextension of the PIP joint range from surgery to splinting techniques [2]. Silver ring splints (SRSs) were recently identified as a possible alternative to surgery and traditional thermoplastic splints because patient adherence was improved by their appearance [3]. The objective of this study was to investigate whether the SRSs restrict PIP joint hyperextension during a fine dexterity task

Quasiparticle transport equation with collision delay. II. Microscopic Theory

For a system of non-interacting electrons scattered by neutral impurities, we derive a modified Boltzmann equation that includes quasiparticle and virial corrections. We start from quasiclassical transport equation for non-equilibrium Green's functions and apply limit of small scattering rates. Resulting transport equation for quasiparticles has gradient corrections to scattering integrals. These gradient corrections are rearranged into a form characteristic for virial corrections

Transport Dynamics of Broad Resonances

The propagation of short life time particles with consequently broad mass width are discussed in the context of transport descriptions. In the first part some known properties of finite life time particles such as resonances are reviewed and discussed at the example of the $\rho$-meson. Grave deficiencies in some of the transport treatment of broad resonances are disclosed and quantified. The second part addresses the derivation of transport equations which permit to account for the damping width of the particles. Baym's $\Phi$-derivable method is used to derive a self-consistent and conserving scheme, which fulfils detailed balance relations even in the case of particles with broad mass distributions. For this scheme a conserved energy-momentum tensor can be constructed. Furthermore, a kinetic entropy can be derived which besides the standard quasi-particle part also includes contributions from fluctuations.Comment: Talk presented on the Erice School on Nuclear Physics, Erice, Italy, Sept. 17 - 25, 1998 to be published in Progress in Particle and Nuclear Physics, Vol. 42 (10 pages, 5 eps-figures

Exact Conservation Laws of the Gradient Expanded Kadanoff-Baym Equations

It is shown that the Kadanoff-Baym equations at consistent first-order gradient approximation reveal exact rather than approximate conservation laws related to global symmetries of the system. The conserved currents and energy-momentum tensor coincide with corresponding Noether quantities in the local approximation. These exact conservations are valid, provided a Phi-derivable approximation is used to describe the system, and possible memory effects in the collision term are also consistently evaluated up to first-order gradients.Comment: 26 pages, feynman.package for diagrams, submitted to Annals of Physic

The effect of memory on relaxation in a scalar field theory

We derive a kinetic equation with a non-Markovian collision term which includes a memory effect, from Kadanoff-Baym equations in $\phi^4$ theory within the three-loop level for the two-particle irreducible (2PI) effective action. The memory effect is incorporated into the kinetic equation by a generalized Kadanoff-Baym ansatz.Based on the kinetic equations with and without the memory effect, we investigate an influence of this effect on decay of a single particle excitation with zero momentum in 3+1 dimensions and the spatially homogeneous case. Numerical results show that, while the time evolution of the zero mode is completely unaffected by the memory effect due to a separation of scales in the weak coupling regime, this effect leads first to faster relaxation than the case without it and then to slower relaxation as the coupling constant increases.Comment: 12 pages, 6 eps figure