Spectroscopy is one of the fundamental tool in condensed matter physics, materials science and nanoscience. Resonant spectroscopies, like Resonant Inelastic X-ray Scattering (RIXS) and angle resolved Resonant PhotoEmission Spectroscopy (RPES), offer invaluable information on the system under investigation, being able to probe different types of excitations, from electron-hole pairs (excitons), to ...