### Résumé du preprint DAPNIA-07-208

DAPNIA-07-208
Generalised parton distributions at HERA and prospects for COMPASS.
L. Schoeffel
 We present a model of generalised parton distributions based on a forward ansatz
in the DGLAP region. We discuss some aspects of the parametrisations, as the dependence
in t, with factorised and non-factorised approaches, where t is the square of the
four-momentum exchanged at the hadron vertex. The predictions of this model are
then compared with DVCS cross sections from H1 and ZEUS, and a related observable,
the skewing factor, defined as the following ratio imaginary amplitudes :
$R \\equiv {Im {\\cal A} (\\gamma^*+p \\to \\gamma +p)\\lfrestriction{t=0}} / {Im {\\cal A} (\\gamma^*+p \\to \\gamma^* +p)\\lfrestriction{t=0}}$.
It is an interesting quantity including both the non-forward kinematics and
the non-diagonal effects. Finally, we discuss the beam charge asymmetry, which is
certainly the most sensitive observable to the different hypothesis needed in the
GPDs parametrisations. We show that the approximations done for the t dependence
lead to significant differences for the predictions in the HERMES kinematic domain and
prospects are given for COMPASS.