Forschung im HLRN-Verbund 2011

181Figure 1: Barycentric ‘density plot’ of the distribution (probability) amplitude of a spin-up proton as a function of themomentum fractions of the valence spin up quark (x 1 ), and the up (x 2 ) and down (x 3 ) di-quarks (withx 1 + x 2 + x 3 = 1). The lines of constant x 1 , x 2 and x 3 are parallel to the sides of the triangle labelled byx 2 , x 3 and x 1 .less quarks and pions may exist at all. Perhaps itshows that the physical constants are constitutedin a way that allows the conditions necessary forlife, the anthropic principle.Calculations of a wide class of observables arenow becoming available at physical pion masses,so direct comparison with experiment, i.e. withoutextrapolation to the physical point, will soon bepossible. However, finite size effects are startingto become a serious issue. This is not surprising,given the fact that the nucleon barely fits into thevolumes simulated so far. As a result, we are nowplanning new simulations on volumes of (5 fm) 3 , inorder to minimize finite volume corrections. Thelong-term goal is to extend the calculations to latticespacings a ≤ 0.05 fm, which correspond to momentumcut-offs ≥ 4 GeV, so as to accommodatecharmed quarks on the lattice. Charm physics isone of the main research topics at GSI/FAIR. Toreach this goal, O(100) Petaflop/s-scale computingfacilities are required.More Information1. V.M. Braun et al.: Nucleon distribution amplitudesand proton decay matrix elements on thelattice, Phys. Rev. D 79 (2009) 034504.2. M. Göckeler et al.: Lattice Investigations of NucleonStructure at Light Quark Masses, PoSLAT2009 (2009) 125 [arXiv:0912.0167 [heplat]].FundingEuropean Union (HadronPhysics2); DFG CollaborativeResearch Centre Transregio 55Figure 2: The anomalous magnetic moment of proton minus neutron as a function of the pion mass for three differentcouplings, corresponding to lattice spacings ranging from a = 0.080 fm (β = 5.25) to a = 0.069 fm(β = 5.40), compared to the experimental value (∗) at the physical pion mass.Physik