Recommendations
The main goal of the first meeting of Working Group 1 was to compare and
contrast the different theoretical approaches that are available to
analyse the properties of strongly interacting matter in equilibrium,
both in the hadronic gas and in the quark-gluon plasma. These methods
include lattice QCD, effective models, the hadron resonance gas and
holography. While all of these approaches are being used, there is not
always sufficient cross-talk between the practitioners. Moreover, the
physics input and understanding of pending questions can be quite
distinct. For instance, in lattice QCD the emphasis is on high-quality
data and the extraction of basic quantities, such as hadronic masses in
the low-temperature phase and indications of melting of hadrons in the
high-temperature phase. In the hadron resonance gas model on the other
hand, the physics input is taken from concepts that arise in nuclear
physics, such as attractive and repulsive channels, phase shifts, and
excluded volumes. These concepts are not easily accessible on the
lattice. Holographic methods can provide qualitative insights on the
behavior of strongly interacting matter in theories that are similar to
QCD and hence yield an important tool to explore new phenomena, focusing
on universal features. These phenomena can then be further investigated
using effective models or simulations of lattice QCD, in order to arrive
at quantitative understanding.
The first recommendation that emerged from the first WG1 meeting is to
establish closer contacts between the various research activities and
encourage a close and critical comparison of input, methods and results,
with the aim of formulating a description of hot matter which
incorporates insight from lattice QCD, effective theories, nuclear
physics and holography. This can be achieved by bringing together
researchers at workshops where dedicated time is devoted to discussion,
to stimulate understanding and exchange of ideas (such as at the first
WG1 meeting). A second recommendation is to compare the physics
predictions quantitatively, and highlight any discrepancies, with the
aim of removing those by more advanced descriptions. Again sufficient
discussion and collaboration time should be devoted to this.