Search

We present a lattice calculation of the renormalized running coupling constant in symmetric (MOM) and asymmetric $ \left( {\widetilde{\mathrm{MOM}}} \right) $ momentum substraction schemes including u, d, s and c quarks in the sea. An Operator Product Expansion dominated by the dimension-two 〈 A〉 condensate is used to fit the running of the coupling. We argue that the agreement in the predicted 〈 A〉 condensate for both schemes is a strong support for the validity of the OPE approach and the effect of this non-gauge invariant condensate over the running of the strong coupling. [ABSTRACT FROM AUTHOR]

For a relativistic system of two scalar particles, we find the Bethe-Salpeter amplitude in Minkowski space and use it to compute the electromagnetic form factor. The comparison with Euclidean space calculation shows that the Wick rotation in the form factor integral induces errors which increase with the momentum transfer Q2. At JLab domain ( Q2 = 10 GeV^2/c2), they are about 30%. Static approximation results in an additional and more significant error. On the contrary, the form factor calculated in light-front dynamics is almost indistinguishable from the Minkowski space one. [ABSTRACT FROM AUTHOR]

The electromagnetic form factors (FF’s) calculated through the Euclidean Bethe-Salpeter (BS) amplitude and through the light-front (LF) wave function are compared with the one found using the BS amplitude in Minkowski space. The FF expressed through the Euclidean BS amplitude (both within and without static approximation) considerably differs from the Minkowski one, whereas the FF found in the LF approach is almost indistinguishable from it. [ABSTRACT FROM AUTHOR]