Present and future challenges for quark matter theorists

Abstract

We review some theoretical challenges in the quest for understanding quark matter. Several contributions to the Strangeness in Quark Matter 2007 Conference indicated problems to be solved and methods to be developed further. This summary gives an individual review of questions held to be important by the author.

Hot and dense hadronic matter in an effective mean-field approach

“…This behavior is in agreement with recent relativistic heavy-ion collision data [71]. 2 It is proper to remember that in this approach we are not considering effective meson masses, neglecting, for example, the repulsive potential for kaons and the attractive potential for antikaons [69,70]. Therefore, differences could occur between the present treatment and more sophisticated formulations.…”

“…The determination of the properties of nuclear matter as function of density and temperature is a fundamental task in nuclear and subnuclear physics. Heavy ion collisions experiments open the possibility to investigate strongly interacting compressed nuclear matter exploring in laboratory the structure of the QCD phase diagram [1][2][3][4]. The extraction of information about the Equation of State (EOS) at different densities and temperatures by means of intermediate and high energy heavy ion collisions is a very difficult task and can be realized only indirectly by comparing the experimental data with different theoretical models, such as, for example, fluid-dynamical models.…”

“…(Color online) Ratios of net densities ++ /p as a function of the baryon chemical potential for different temperatures, r s , and parameter sets (a, TM1; b, NLρδ; c, GM3).the (positive) ω-meson field one and, thus, kaon condensation can occur only at very high baryon densities 2. …”

Nonextensive statistical effects in the hadron to quark–gluon phase transition

“…It is important to observe that Eq.s (14), (18) and (19) apply to n q i ≡ (n i ) q rather than n i itself, this is a direct consequence of the basic prescription related to the q-mean expectation value in nonextensive statistics [20,40] (this recipe was not adopted in Ref. [42]).…”

Nonextensive statistical effects and strangeness production in hot and dense nuclear matter

“…The process of deconfinement and the equation of state (EOS) of hot and dense nuclear matter can in principle be described by QCD, however such a theory is highly non-perturbative in the energy density range involved in relativistic heavy-ion collisions. The generated quark-gluon plasma (QGP) in the early stages of the collisions does not at all resemble a quasi-ideal gas of quarks and gluons because strongly dynamical correlations are present, including long-range interactions [9,10,11]. Therefore, in the absence of a converging method to approach QCD at finite density one has often to resort to effective and phenomenological model investigations to obtain qualitative results.…”