2003/07/29 by S. Juchem, W. Cassing, C. Greiner +1 · 10 citations
Physics and Astronomy · #Cold Atom Physics and Bose-Einstein Condensates #Quantum Electrodynamics and Casimir Effect #Quantum, superfluid, helium dynamics #hep-ph #nucl-th
paper · pdf · doi:10.1103/physrevd.69.025006
published as Phys.Rev. D69 (2004) 025006 · 77 pages, 26 figures
arxiv created 2003/07/29 · openalex publication_date 2004/01/30 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The quantum time evolution of \ensuremathφ4-field theory for a spatially homogeneous system in 2+1 space-time dimensions is investigated numerically for out-of-equilibrium initial conditions on the basis of the Kadanoff-Baym equations including the tadpole and sunset self-energies. Whereas the tadpole self-energy yields a dynamical mass, the sunset self-energy is responsible for dissipation and an equilibration of the system. In particular we address the dynamics of the spectral (``off-shell'') distributions of the excited quantum modes and the different phases in the approach to equilibrium described by Kubo-Martin-Schwinger relations for thermal equilibrium states. The investigation explicitly demonstrates that the only translation invariant solutions representing the stationary fixed points of the coupled equation of motions are those of full thermal equilibrium. They agree with those extracted from the time integration of the Kadanoff-Baym equations for \stackrel\ensuremath→t\ensuremath∞. Furthermore, a detailed comparison of the full quantum dynamics to more approximate and simple schemes such as that of a standard kinetic (on-shell) Boltzmann equation is performed. Our analysis shows that the consistent inclusion of the dynamical spectral function has a significant impact on relaxation phenomena. The different time scales that are involved in the dynamical quantum evolution towards a complete thermalized state are discussed in detail. We find that far off-shell 1\ensuremath↔3 processes are responsible for chemical equilibration, which is missed in the Boltzmann limit. Finally, we briefly address the case of (bare) massless fields. For sufficiently large couplings \ensuremathλ we observe the onset of Bose condensation, where our scheme within symmetric \ensuremathφ4 theory breaks down.