Multiple scattering and induced parton splitting lead to a medium modification of the QCD evolution for jet fragmentation functions and final hadron spectra. Medium-induced parton splittings not only lead to energy loss of leading partons and suppression of leading hadron spectra, but also modify the flavor composition of a jet due to induced flavor conversion via gluon emission and quark pair production and annihilation. Through a numerical study of the medium-modified QCD evolution, leading K- strange meson spectra are found to be particularly sensitive to the medium-induced flavor conversion in semi-inclusive deeply inelastic scatterings (SIDIS) off a large nucleus. The induced flavor conversion can lead to an increased number of gluons and sea quarks in a jet shower and, as a consequence, enhance the leading K- spectrum to counter the effect of parton energy loss in SIDIS with large momentum fractions xB, where the struck quarks are mostly valence quarks of the nucleus.

Heavy-ion collisions at very high colliding energies are expected to produce a quark-gluon plasma (QGP) at the highest temperature obtainable in a laboratory setting. Experimental studies of these reactions can provide an unprecedented range of information on properties of the QGP at high temperatures. We report theoretical investigations of the physics perspectives of heavy-ion collisions at a future high-energy collider. These include initial parton production, collective expansion of the dense medium, jet quenching, heavy-quark transport, dissociation and regeneration of quarkonia, photon and dilepton production. We illustrate the potential of future experimental studies of the initial particle production and formation of QGP at the highest temperature to provide constraints on properties of strongly interaction matter.