  We present a calculation of the quasiparticle decay rate due to
electron-electron interactions in a doped graphene sheet. In particular, we
emphasize subtle differences between the perturbative calculation of this
quantity in a doped graphene sheet and the corresponding one in ordinary
parabolic-band two-dimensional (2D) electron liquids. In the random phase
approximation, dynamical overscreening near the light cone yields a universal
quasiparticle lifetime, which is independent of the dielectric environment
surrounding the 2D massless Dirac fermion fluid.
