Jet quenching parameter in an expanding QCD plasma

We present a new definition of the jet quenching parameter $\widehat{q}$ in a weakly-coupled quark-gluon plasma undergoing boost-invariant longitudinal expansion. We propose a boost-invariant definition of $\widehat{q}$, which is proportional to the broadening of the angular variables $\eta$ (the pseudo-rapidity) and $\varphi$ (the azimuthal angle). We furthermore consider radiative corrections to $\widehat{q}$ and find potentially large corrections enhanced by a double logarithm like the case of a static medium. But unlike for the static medium, these corrections are now local in (proper) time.