Baryon resonances in a chiral hadronic model for the QCD equation of state

Abstract

In this paper we study the influence of hadronic resonances on the phase diagram calculated with an effective chiral flavour SU(3) model. We show that varying the couplings of the baryonic resonances to the attractive scalar and the repulsive vector fields has a major impact on the order and location of the chiral phase transition and the possible existence of a critical end point as well as on the thermodynamic properties of the model. Furthermore, we study (strange) quark number fluctuations and show the related susceptibilities both at zero baryochemical potential and when crossing the phase transition line at three different points in the T-mu plane. We obtain the best agreement with current lattice data if we choose a rather strong vector coupling which in our model limits the phase transition to a smooth crossover and implies the non-existence of a critical end point

Chiral hadronic mean field model including quark degrees of freedom

“…In this case, at the critical temperature T c = 164 MeV, which quantitatively agrees well with recent lattice data, σ falls off in a small temperature range. As already pointed out in [43], a slower decrease of σ , as it is observed in the lattice data, can be achieved by taking into account pionic self interactions [88][89][90]. Nevertheless, as predicted by all lattice QCD calculations, the transition is a smooth cross-over for both order parameters.…”

“…The couplings of the baryonic octet are fixed such as to reproduce the well-known vacuum masses and nuclear saturation properties (see [56,60] for details). For the couplings of the baryonic resonances to the fields, a straight forward two parameter ansatz is chosen [43]. This approach avoids having multiple different coupling parameters for every single resonance state or SU(3) multiplets.…”

“…where r s and r v are the so-called scaling parameters for the scalar and vector fields. Reference [43] demonstrates the impact of baryonic resonance states on the phase diagram. This was essentially done by varying the vector coupling strength (change the value of r v , which effectively controls the abundance of particles at finite baryochemical potentials in the model).…”

“…Besides direct numerical approaches solving the QCD Lagrangian, a broad range of effective theoretical models exist for describing known properties of the phase diagram and thermodynamic characteristics of strongly interacting matter [5,[34][35][36][37][38][39][40]. In this paper, such a model is presented including all known hadronic degrees of freedom [41][42][43][44] as well as a quark phase for the description of highly excited matter. With this model, it is possible to study the QCD phase diagram with a particular focus on the phase transitions.…”

Magnetic moments of the low-lying $$\tfrac{1} {2}^ -$$ octet baryon resonances

“…The näive quark model has been further extended by implementing the chiral symmetry and its spontaneous breaking to it [5], giving rise to the chiral constituent quark model (χCQM), which as a result includes the important phenomenon of quark-antiquark excitations, in other words the presence of the meson cloud at low energies. This perspective is in common with the modern effective field theory approaches used to study the baryon resonances [6][7][8][9][10][11][12][13][14].…”