Nucleon distribution amplitudes and proton decay matrix elements on the lattice

Baryon distribution amplitudes (DAs) are crucial for the theory of hard exclusive reactions. We present a calculation of the first few moments of the leading-twist nucleon DA within lattice QCD. In addition we deal with the normalization of the next-to-leading (twist-four) DAs. The matrix elements determining the latter quantities are also responsible for proton decay in grand unified theories. Our lattice evaluation makes use of gauge field configurations generated with two flavors of clover fermions. The relevant operators are renormalized nonperturbatively with the final results given in the MS̅ scheme. We find that the deviation of the leading-twist nucleon DA from its asymptotic form is less pronounced than sometimes claimed in the literature.Vladimir M. Braun, Meinulf Göckeler, Roger Horsley, Thomas Kaltenbrunner, Yoshifumi Nakamura, Dirk Pleiter, Paul E. L. Rakow, Andreas Schäfer, Gerrit Schierholz, Hinnerk Stüben, Nikolaus Warkentin and James M. Zanotti (QCDSF Collaboration