Orateur
Description
Generalized parton distributions (GPDs) are off-forward matrix elements of quark and gluon operators that work as a window to the total angular momentum of partons and their transverse imaging (nucleon tomography). To access GPDs one needs to look into exclusive processes, out of which double deeply virtual Compton scattering (DDVCS) is a promising mechanism to measure GPDs outside the lines $x=\pm\xi$ at leading order (which is a restriction in DVCS and TCS cases). Here, $x$ represents the average longitudinal momentum carried by an active parton, while $\xi$ is the skewness parameter.
These aforementioned exclusive processes are usually studied in a kinematic regime known as the Björken limit, where the photon virtualities are much larger than the hadron mass $M$, and the kick to the hadron measured by the Mandelstam's variable $t$. This is not enough for the purposes of precise GPD extraction or nucleon tomography, for which measurements in a sizable range of $t$ are required. Deviation with respect to the Björken limit induces the kinematic higher-twist corrections which enter the amplitudes with powers of $|t|/Q^2$ and $M^2/Q^2$, where $Q^2$ denotes the scale of process (sum of photon virtualities in the case of DDVCS).
In this talk, I present novel calculations of DDVCS off a (pseudo-)scalar target up to first order power corrections (twist-4). These results are important for measuring DDVCS, DVCS and TCS through the Sullivan process and off helium-4 target at the future Electron-Ion Collider (EIC) and JLab experiments.
