The Virtue of Being Virtual

The photon that left your computer screen and just hit your retina now certainly was a ‘real’ photon. Right? Well, not so fast. Sketch the Feynman diagram for the process. The photon was emitted by an atom in the screen, and absorbed by an atom in your retina. The diagram is indistinguishable from that for a virtual process- it’s all a matter of scale. (more…)

Electromagnetic Radiation at RHIC

Electromagnetic radiation from nuclear collisions at RHIC energies

Dileptons and direct photons can carry information on the thermodynamic state of the deconfined medium at the moment of production – since they interact only electromagnetically they can leave the hot and dense reaction zone basically undistorted, making them valuable and direct probes of the intermediate QGP phase of the heavy-ion reaction. (more…)

Physics of anisotropic quark-gluon plasmas

A rapidly expanding quark-gluon plasma, as it is formed in a relativistic heavy ion collision, is characterized by an anisotropic momentum distribution of partons. An anisotropic quark-gluon plasma exhibits peculiar properties, such as soft-mode instabilities, which have attracted much interest in recent years. (more…)