  Dilepton production in relativistic heavy-ion collisions is studied within
the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach, which
is based on a dynamical quasiparticle model (DQPM) matched to reproduce lattice
QCD results in thermodynamic equilibrium. A comparison to the data of the NA60
Collaboration for In+In collisions at 158 AGeV shows that the dilepton spectra
are well described by the sum of hadronic and partonic sources, if a
collisional broadening of vector mesons is taken into account as well as the
off-shell quark-antiquark annihilation (q+qbar->l^+l^- and q+qbar->gl^+l^-) in
the QGP. In particular, the observed softening of the mT spectra at
intermediate masses is reproduced. The data of the PHENIX collaboration on
dilepton production in Au+Au collisions at sqrt(s)=200 GeV for masses above 1
GeV are found to be dominated by the contributions of the QGP radiation and the
charm meson decays, while the measured spectrum is underestimated in the mass
range from 0.2 to 0.6 GeV.
