  We address the dilepton production from the parton interactions in the early
stage of relativistic heavy-ion collisions within the parton-hadron-string
dynamics (PHSD) off-shell transport approach. The description of partons in
PHSD is based on the dynamical quasiparticle model (DQPM) matched to reproduce
lattice QCD results in thermodynamic equilibrium. According to the DQPM the
constituents of the strongly interacting quark-gluon plasma (sQGP) are massive
and off-shell quasi-particles (quarks and gluons) with broad spectral
functions. In order to address the electromagnetic radiation of the sQGP, we
derive off-shell cross sections of q+qbar->gamma*, q+qbar->gamma*+g and
q+g->gamma*+q (qbar+g->gamma*+qbar) reactions taking into account the effective
propagators for quarks and gluons from the DQPM. Dilepton production in In+In
collisions at 158 AGeV and in Au+Au at sqrt(s)=200 GeV is calculated by
implementing these off-shell processes into the PHSD transport approach. By
comparing to the data of the NA60 and PHENIX Collaborations, we study the
relative importance of different dilepton production mechanisms and point out
the regions in phase space where partonic channels are dominant.
