  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 which are usually studied in a
kinematic regime known as the Bj\"orken limit. In this limit, the photon
virtualities are much larger than the hadron mass $M$, and the kick to the
hadron measured by the Mandelstam's variable $t$. It turns out that this is not
enough for the purposes of a precise GPD extraction and, in particular, of
nucleon tomography for which measurements in a sizable range of $t$ are
required. Deviation with respect to the Bj\"orken limit induces kinematic
higher-twist corrections which enter the amplitudes with powers of
$|t|/\mathbb{Q}^2$ and $M^2/\mathbb{Q}^2$, where $\mathbb{Q}^2$ denotes the
scale of the process (basically, the sum of photon virtualities in the case of
DDVCS). There are also corrections by the name of "genuine" higher twists which
are a separate topic and are not the subject of this research study.
  In this manuscript, we present novel calculations of DDVCS amplitudes off a
(pseudo-)scalar target including up to kinematic twist-4 corrections. 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. Preliminary numerical estimates for the pion target are
provided.
