Fluctuation-induced modifications of the phase structure in ( 2+1 )-flavor QCD

Abstract

The low-energy sector of QCD with N f = 2+1 dynamical quark flavors at non-vanishing chemical potential and temperature is studied with a non-perturbative functional renormalization group method. The analysis is performed in different truncations in order to explore fluctuation-induced modifications of the quark-meson correlations as well as quark and meson propagators on the chiral phase transition of QCD. Depending on the chosen truncation significant quantitative implications on the phase transition are found. In the chirally symmetric phase, the quark flavor composition of the pseudoscalar (η, η )-meson complex turns out to be drastically sensitive to fluctuation-induced modifications in the presence of the axial U(1) A anomaly. This has important phenomenological consequences for the assignment of chiral partners to these mesons.

Chiral and U(1)A restoration for the scalar and pseudoscalar meson nonets

“…The ideal limit at asymptotically high temperatures has been confirmed by recent analysis within the linear sigma model [35] and the NJL model [30]. Similar results have been obtained in [36] by studying the influence of quantum and thermal fluctuations on the η − η 0 mixing angle. The above aspects regarding chiral partners and patterns are also of fundamental relevance to clarify the nature of the scalar nonet, which has been a matter of debate over the recent past [37][38][39].…”

“…3(a), we plot the susceptibility combination in the lhs of (36), signaling a vanishing of θ P , from the lattice analysis [4], where we have used the WI in (28) for χ ls P . In addition, we plot in the same figure −χ ls ¼m m s χ 5;disc , which according to (35) should remain nonzero to guarantee that this is a region where θ P ∼ 0.…”

QCD phase structure at finite temperature and density

“…Here we discuss the functional renormalisation group approach to QCD. Our study is based on and extends the work on QCD in [25-29, 31-33, 69] and also draws from results on the QCD phase structure within low energy effective theories (LEFTs), [30,34,[70][71][72][73][74][75][76]. For a selection of fRG studies within LEFTs see [30,34,.…”

“…Furthermore, it is well-known that mild momentumdependences of vertex functions and propagators are well captured by scale-dependent dressing functions; for investigations in QCD and low energy effective models see e.g. [28,70,73,95,131]. This suggests an approximation scheme in which only the dominant nontrivial momentum dependences are taken into account explicitly, while the rest of the dependences is approximated by scaledependent dressings.…”

“…Moreover, in (116) we have implicitly assumed its convergence. It has been shown in [70] that the most rapid convergence of this expansion is achieved if the expansion point κ is kept fixed, for applications see also [28,71,73]. Then the only k-dependence of the expansion point in (116) comes from the mesonic wave function Z φ .…”