Nonequilibrium Quantum-Field Dynamics and Off-Shell Transport for ϕ4\phi^4-theory in 2+1 dimensions

We solve the Kadanoff-Baym equations for nonequilibrium initial configurations of the $\phi^4$-theory in 2+1 dimensions and compare to explicit solutions of generalized transport equations for the same theory. The latter transport equations are derived from the Kadanoff-Baym equation in a first order gradient expansion in phase space and explicitly retain the off-shell dynamics as inherent in the time-dependent spectral functions. The solutions of these equations compare very well with the exact solutions of the full Kadanoff-Baym equations with respect to the occupation numbers of the individual modes, the spectral evolution as well as the chemical equilibration process. Furthermore, the proper equilibrium off-shell distribution is reached for large times contrary to the quasiparticle Boltzmann limit. We additionally present a direct comparison of the solution of the generalized transport equations in the Kadanoff-Baym and Botermans-Malfliet form; both solutions are found to agree very well with each other.Comment: 43 pages, LaTex, including 15 postscript figures, submitted to Nucl. Phys.

Quantum dynamics and thermalization for out-of-equilibrium phi^4-theory

The quantum time evolution of \phi^4-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 in the long time limit. Furthermore, a detailed comparison of the full quantum dynamics to more approximate and simple schemes like 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 3 processes are responsible for chemical equilibration, which is missed in the Boltzmann limit. Finally, we address briefly the case of (bare) massless fields. For sufficiently large couplings $\lambda$ we observe the onset of Bose condensation, where our scheme within symmetric \phi^4-theory breaks down.Comment: 77 pages, 26 figure

Interactive Television : between Trend and Misunderstanding

nicht vorhandenThe idea of an interactive television is not new. In fact, ZDF broadcasted the first interactive program, „Der goldene Schuss“ (The Golden Shot), on German TV in 1964. From that point on, the integration of the viewer in television programming gained in importance. Whether via telephone, fax or text message, the viewer should participate. Even in this day and age of frenzied-pace of media change, interactive television is popular and has as established itself as a trend for viewers. With the help of the internet, the feeling of interactive viewing is facilitated with digital applications, social networking and modern televisions. This thesis researches interactive television’s potential, which despite its long historic is still waiting on a new breakthrough and is on the fringes of its future form. Discussion on how different broadcasters understand and implement the concept of interactive programming, how it is accepted by the public, and whether interactive television is sustainable is included. The presented research was based on a theoretical compilation construction and through the questioning of experts this thesis is concluding in recommended actions for broadcasters and recommendation for future research