Quantum dynamics and thermalization for outofequilibrium φ^{4} theory
Abstract
The quantum time evolution of φ^{4}field theory for a spatially homogeneous system in 2+1 spacetime dimensions is investigated numerically for outofequilibrium initial conditions on the basis of the KadanoffBaym equations including the tadpole and sunset selfenergies. Whereas the tadpole selfenergy yields a dynamical mass, the sunset selfenergy is responsible for dissipation and an equilibration of the system. In particular we address the dynamics of the spectral (“offshell”) distributions of the excited quantum modes and the different phases in the approach to equilibrium described by KuboMartinSchwinger 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 KadanoffBaym equations for t→∞. Furthermore, a detailed comparison of the full quantum dynamics to more approximate and simple schemes such as that of a standard kinetic (onshell) 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 offshell 1↔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 λ we observe the onset of Bose condensation, where our scheme within symmetric φ^{4} theory breaks down.
 Publication:

Physical Review D
 Pub Date:
 January 2004
 DOI:
 10.1103/PhysRevD.69.025006
 arXiv:
 arXiv:hepph/0307353
 Bibcode:
 2004PhRvD..69b5006J
 Keywords:

 05.70.Ln;
 05.60.k;
 11.10.Wx;
 24.10.Cn;
 Nonequilibrium and irreversible thermodynamics;
 Transport processes;
 Finitetemperature field theory;
 Manybody theory;
 High Energy Physics  Phenomenology;
 Nuclear Theory
 EPrint:
 77 pages, 26 figures