The research in the team of professor Andersen is aimed at understanding in detail the phase diagram of Quark-Gluon Plasma (QCD).

The phases of quark-gluon plasma (QCD)

If hadronic matter is heated, it is expected to undergo a phase transition to a new state of matter called the quark-gluon plasma. This can be seen by following the vertical temperature axis to the upper left corner in the figure (fig.1).

In the quark-gluon plasma, the quarks are no longer confined in hadrons, but can move freely around much in the same way as in ordinary plasmas.

The chiral symmetry, which was broken at low temperatures, is restored in the high-temperature quark-gluon phase. In order to examine the properties of the high-temperature phase, there is currently a large experimental activity aiming at creating a quark-gluon plasma. At present the only way of producing it is in heavy-ion collisions.

Similarly, one can ask what happens to strongly interacting matter as one increases the density. This can be seen by following the horizontal axis to the lower right corner in the figure. In this case, one expects that QCD undergoes a phase transitions to a state called quark matter in which quarks are no longer confined. If the temperature is sufficiently low, quark matter might also be a colour superconductor. Colour superconductivity is analogous to ordinary superconductivity, but there can be various colour-superconducting phases.

The phase diagram at high density is very relevant to astrophysics since astrophysical objects such as neutron stars might have a core whose density is several times the density of ordinary nuclear matter.