Project Description      

Considerable progress in the area of nonequilibrium field theory has been made in recent years. Theoretical advances include first-principles derivation of transport coefficients and effective kinetic theory at arbitrary temperatures in weakly coupled scalar theories, analysis of the effects of damping in gauge theories and the associated construction of effective theories for the low frequency modes, and systematic studies of decoherence and effective damping in the large N limit (where a Gaussian mean field approximation provides the first term in a systematic expansion). There is also vigorous activity in the study of topological transitions at finite temperature and the quantum theory for the nucleation and transport of nonlinear coherent structures such as vortices and kinks.

As a result of recent advances in high performance computing, quantitative attacks are now possible on a host of outstanding, but until recently quite intractable, problems in quantum field theories under nonequilibrium conditions. Specific examples of current interest involving nonequilibrium dynamics of field theories include (but are not limited to) electroweak baryogenesis and topological transition rates, post-inflationary reheating in the early universe, dynamics of vortices in Bose-Einstein condensates, and chiral condensates and evolution of the quark-gluon plasma in heavy ion collisions.

In addition to these specific applications, many theoretical aspects of nonequilibrium QFT involve a fascinating (and challenging) interplay of quantum dynamics and coherence, statistical mechanics, kinetic theory, and thermodynamics.

As part of our project, research has been carried out in the following areas:

Baryon number violation

RHIC physics

Nucleation and transport of nonlinear coherent structures

Nonequilibrium phase transitions

Quantum dynamics in cavity QED and atomic optics

We have substantial expertise in both theoretical analysis and numerical computations in the above fields. Almost exclusively, all our simulations to date have been performed on parallel computing platforms including the Thinking Machines CM-200 and CM-5, the SGI/Cray Origin 2000, and the Cray T3E. We will soon be using IBM SP and Compaq systems and have designed and constructed our own 72-processor commodity cluster for medium scale use. Below we describe in more detail the research plan for each sub-topic as well as the existing and planned numerical machinery.

Recently developed techniques in nonequilibrium quantum field theory are being used to study the quantum transport of nonlinear coherent structures such as kinks, domain walls, and vortices. Our first aim is to find and investigate stability properties of self-consistent (mean field plus fluctuations) kink solutions for sine-Gordon and Landau-Ginzburg theories. We will then investigate low temperature transport properties of these self-consistent nonlinear structures. The method we use here is the leading order 1/N expansion, numerical codes for which have already been implemented by us on the T3E. These codes need to be modified to handle inhomogeneous problems (this is required to study soliton transport problems as described above). Another target is to investigate the transport properties of vortices in a two-dimensional complex Landau-Ginzburg theory by similar methods. We have completed an investigation of the classical finite temperature vortex transport in this model by direct numerical solution of the field theoretic Langevin equation. Due to resource limitations, this work will not be carried out at NERSC in FY01.

Examples of evolution out of thermal equilibrium include such diverse phenomena as phase transitions in the early universe, ultrarelativistic heavy-ion collisions leading to a transition to a new phase of nuclear matter, and flux flow in superconductors. When a system is driven out of equilibrium, it may remain in a metastable phase or steady state for very long times and show nonexponential relaxation. A special feature of these processes is the history dependence of the final state. These problems can be studied by 1/N methods in nonequilibrium field theory. We have already investigated nonequilibrium dynamics of a Landau-Ginzburg theory using this technique. We propose to extend this work by taking into account the next order 1/N correction which will enable us to include the rescattering of fluctuations which controls the eventual thermalization of the system. A parallel code for the leading order calculation has been ported to the T3E and a new code will be written that includes the next order correction. (Theoretical work is now in progress.) For FY01 we expect to focus on RHIC physics and investigate the dynamics of the quark-gluon phase transition via stochastic partial differential equations with renormalized parameters (to eliminate cut-off dependences).

Cavity QED and atomic optics has become an excellent testing ground for fundamental ideas in nonequilibrium quantum dynamics. Over the last 5 years we have written large, parallel, split-operator codes for solving quantum Master equations for these problems. These codes, along with some new ones written and implemented in FY98/99, have already been tested and run on the T3E. In production mode, we plan to use these codes for analysis and design of new experiments which will be carried at UT, Austin and at Caltech. New codes are being written to investigate problems in the emerging technology of quantum feedback control as part of a recently initiated Los Alamos - Caltech collaboration. (This part of the effort will be discontinued as part of our work on nonequilibrium field theory and will be proposed as a separate research actvity for FY01.)

Salman Habib / LANL / habib@lanl.gov / revised August 00