Is the nucleon deformed ?

A property of Quantum Chromodynamics (QCD) which should be included into effective models describing QCD at low energies is chiral symmetry. It is conserved if one assumes that the quark masses are zero. This symmetry is spontaneously broken, which leads to constituent quark and as the Goldstone Boson one obtains the pion and its chiral partner, the σ meson. We use the linear σ model which has, compared to the nonlinear one, the advantage that one treats pions and σ mesons not only on the chiral cycle, but allows also fluctuations around it. The scale of this fluctuations is the σ meson mass. If one eliminates gluons in second order, one obtains 'Tuebingen chiral quark model' with effective gluon exchange between the quarks and with pions and σ mesons. A confinement potential is added. With this model we describe the photo and electro-excitation of the nucleon into the delta resonance and the decay of this resonance into a nucleon and a pion. The angular distribution gives information about the C2/E2 admixture into the M1 transition from the nucleon to the delta resonance. The quadrupole contributions of this transition has been described in the past by d state admixture due to tensor forces from the gluon and the pion exchange. This yields values which are more then a factor 10 too small compared with recent data for the C2/E2 Sachs transition form factor. We show that meson and gluon pair exchange current can explain the data without the need of a large nucleon or delta deformation. The same model is than used to describe the nucleon-nucleon phase shift. An essential ingredient for the good agreement is to include to all orders couplings to Δ channels. The 1S0 phase shift can only be described in agreement with the data if the coupling to the 5D0 nucleon delta channel is included. (author)