LPM Interference and Cherenkov-like Gluon Bremsstrahlung in Dense Matter

Gluon bremsstrahlung induced by multiple parton scattering in a finite dense medium has a unique angular distribution with respect to the initial parton direction. A dead-cone structure with an opening angle $\theta^2_0 \approx 2(1-z)/(zLE)$ for gluons with fractional energy $z$ arises from the Landau-Pomeranchuck-Migdal (LPM) interference. In a medium where the gluon's dielectric constant is $\epsilon >1$, the LPM interference pattern is shown to become Cherenkov-like with an increased opening angle determined by the dielectric constant $\cos^2\theta_c=z+(1-z)/\epsilon$. For a large dielectric constant $\epsilon \gg 1+2/z^2LE$, the corresponding total radiative parton energy loss is about twice that from normal gluon bremsstrahlung. Implications of this Cherenkov-like gluon bremsstrahlung to the jet correlation pattern in high-energy heavy-ion collisions is discussed.