Dortmund 2006 – wissenschaftliches Programm

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T: Teilchenphysik

T 405: QFT I

T 405.6: Gruppenbericht

Mittwoch, 29. März 2006, 18:00–18:20, C2-02-176

Lattice QCD near the light cone — •Daniel Grünewald and Hans-Jürgen Pirner — Institut für theoretische Physik, Universität Heidelberg, Philosophenweg 19, 69120 Heidelberg

We investigate SU(2) lattice QCD formulated in "near light-cone (NLC)"-coordinates. NLC-coordinates allow a smooth transition from ordinary Minkowski-coordinates to light-cone-coordinates. This makes them physically very appealing, since they are the natural choice in order to describe partons in high energy scattering. A standard eucledian path integral treatment in NLC-coordinates is ruled out by the fact that the action is complex. Therefore we work in the Hamiltonian framework. We derive the Hamiltonian with the transfer matrix method and try to find its ground state by a guided random walk algorithm. If the exact light cone is approached, the NLC Hamiltonian splits into two pieces from which one is dominant. In order to guide the Monte Carlo into regions where the exact ground state wavefunctional is large we compute analytically the ground state of the dominant part of the Hamiltonian in the "A₋=0"-gauge. The dominant term of the NLC Hamiltonian has the same structure as the Hamiltonian of a particle coupled to an electromagnetic field in ordinary QM. Therefore a standard diffusion quantum Monte Carlo treatment does not apply because of the emergence of complex phases due to terms linear in the momentum operator which make the sampling ineffective. To solve this problem we search for an appropriate unitary transformation of the NLC Hamiltonian which eliminates the terms linear in the momentum operator making a numerical treatment of the unitary equivalent Hamiltonian possible.