Basic concepts and recent applicationsof the light-cone path integral approachto the medium-induced energy loss
The basic ideas of the light-cone path integral approach to the induced radiation in QED and QCD and its recent applications to the energy loss effects in QGP and cold nuclear matter are discussed.
The applications include: quark energy loss in QGP and cold nuclear matter; evaluation of the nuclear modification factor for high-$p_T$ hadron production in AA-collisions; medium-induced photon radiation in QGP in AA-collisions. We show that due to the finite-size effects the photon spectrum $propto 1/(1-x)$ contrary to the $1/x$ Bethe-Heitler one. Our calculations, contrary to previous studies, demonstrate that medium effects do not suppress the high-$p_T$ photon production, and even can enhance it. We demonstrate that for RHIC and LHC conditions the induced photon production due to annihilation of high-energy quarks(antiquarks) with thermal antiquarks(quarks) turns out to be very important.
The numerical results are obtained using a new form of the medium-induced spectrum which allows one, for the first time, to perform calculations beyond the oscillator approximation which neglects the Coulomb effects in parton rescatterings.
The role of the finite kinematic bounds is discussed. Our results show that the effect of the kinematic limits is relatively small, contrary to the prediction of Gyulassy, Levai and Vitev.
Landau Institute, Moscou
