On interpretation of fluctuations of conserved charges at high T

Abstract

Fluctuations of conserved charges calculated on the lattice which can be measured experimentally, are well reproduced by a hadron resonanse gas model at temperatures below \(T_{ch} \sim 155\) MeV and radically deviate from the hadron resonance gas predictions above the chiral restoration crossover. This behaviour is typically interpreted as an indication of deconfinement in the quark-gluon plasma regime. We present an argument that this interpretation may be too simple. The argument is based on the scaling of quantities with the number of colors: demonstration of deconfinement and QGP requires observable that is sensitive to \(\sim N_c^2\) gluons while the conserved charges are sensitive only to quarks and above \(T_{ch}\) scale as \(N_c^1\). The latter scaling is consistent with the existence of an intermediate regime characterized by restored chiral symmetry and by approximate chiral spin symmetry which is a symmetry of confining interaction. In this regime the energy density, pressure and entropy density scale as \(N_c^1\). In the large \(N_c\) limit this regime might become a distinct phase separated from the hadron gas and from QGP by phase transitions. A natural observable that associates with deconfinement and is directly sensitive to deconfined \(N_c^2-1\) gluons is the Polyakov loop; in the \(N_c=3\) world it remains very close to 0 at temperatures well above chiral crossover, reaches the value \(\sim 0.5\) around \(\sim 3T_{ch}\) and the value close to 1 at temperatures \(\sim 1\) GeV.