Interests and opportunities to measure Double Deeply Virtual Compton Scattering

The so-called Generalized Parton Distributions (GPDs), containing information about the parton's longitudinal momenta and their transverse position, can be accessed through hard exclusive processes. Double Deeply Virtual Compton Scattering (DDVCS), corresponding to the scattering of a virtual photon off a quark followed by the emission of a photon of different virtuality, is a "golden channel" to study GPDs. Indeed, as for DVCS or TCS (Spacelike and Timelike Deeply Virtual Compton Scattering) it only involves one non-pertubative QCD part, corresponding to GPDs, while other parts can be calculated. In addition, the relative virtuality of the 2 photons provides a lever arm to vary the kinematic points at which we access GPDs, bringing new constrains for tomographic interpretations of the GPDs. We will discuss the interest of measuring DDVCS and some new opportunities at Jefferson Lab.