Electromagnetic structure of the nucleon and the Roper resonance in a light-front quark approach

A relativistic light-front quark model is used to describe both the elastic nucleon and nucleon-Roper transition form factors in a large Q² range, up to 35 GeV² for the elastic and up to 12 GeV² for the resonance case. Relativistic three-quark configurations satisfying the Pauli exclusion principle on the light front are used for the derivation of the current matrix elements. The Roper resonance is considered as a mixed state of a three-quark core configuration and a molecular N+σ hadron component. Based on this ansatz we obtain a realistic description of both processes, elastic and inelastic, and show that existing experimental data are indicative of a composite structure of the Roper resonance.