Superselection rules induced by infrared divergence

Superselection rules induced by the interaction with a mass zero Boson field are investigated for a class of exactly soluble Hamiltonian models. The calculations apply as well to discrete as to continuous superselection rules. The initial state (reference state) of the Boson field is either a normal state or a KMS state. The superselection sectors emerge if and only if the Boson field is infrared divergent, i. e. the bare photon number diverges and the ground state of the Boson field disappears in the continuum. The time scale of the decoherence depends on the strength of the infrared contributions of the interaction and on properties of the initial state of the Boson system. These results are first derived for a Hamiltonian with conservation laws. But in the most general case the Hamiltonian includes an additional scattering potential, and the only conserved quantity is the energy of the total system. The superselection sectors remain stable against the perturbation by the scattering processes.Comment: One reference added; minor corrections in App. B

GPU-based Simulation of Cold Air Flow for Environmental Planning

Simulating the effects of different land-use types regarding flow resistance and cold air production is important for controlling air quality around urban areas. In this paper we present a mathematical model and a simulation method for this problem. This model describes the cold air flow to be composed of two variables. The first is the velocity field which depends on flow resistance and the flow gradient. The second variable is a height field of the cold air which depends on cold air production and advection. To accelerate the simulation and its visualization, it is adapted to run on a GPU(Graphical Processing Unit). Implementing the simulation on fragment shaders makes it possible to combine the height field of the landscape with a color-coded volume rendering of the associated cold-air height. In two passes we compute the cold air height for each time step and render the result to a texture. In a third pass, we render the height field of the landscape using this texure as multi-layered opacity map. urban area forest acre meadow vineyard no data Figure 1: land-use types stimulating cold air production for our simulatio