Functional renormalization group study of the critical region of the quark-meson model with vector interactions
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Regular Article - Theoretical Physics
Functional renormalization group study of the critical region of the quark-meson model with vector interactions Renan Câmara Pereira1,a , Rainer Stiele2,3,4,b , Pedro Costa1,c 1
Department of Physics, Center for Physics of the University of Coimbra (CFisUC), University of Coimbra, 3004-516 Coimbra, Portugal INFN, Sezione di Torino, Via Pietro Giuria 1, 10125 Torino, Italy 3 Département de Physique, ENS de Lyon, Univ Lyon, F-69342 Lyon, France 4 Univ Lyon, Univ Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, F-69622 Villeurbanne, France
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Received: 5 April 2020 / Accepted: 29 July 2020 © The Author(s) 2020
Abstract The critical region of the two flavour quarkmeson model with vector interactions is explored using the Functional Renormalization Group, a non-perturbative method that takes into account quantum and thermal fluctuations. Special attention is given to the low temperature and high density region of the phase diagram, which is very important to construct the equation of state of compact stars. As in previous studies, without repulsive vector interaction, an unphysical region of negative entropy density is found near the first order chiral phase transition. We explore the connection between this unphysical region and the chiral critical region, especially the first order line and spinodal lines, using also different values for vector interactions. We find that the unphysical negative entropy density region appears because the s = 0 isentropic line, near the critical region, is displaced from its T = 0 location. For certain values of vector interactions this region is pushed to lower temperatures and high chemical potentials in such way that the negative entropy density region on the phase diagram can even disappear. In the case of finite vector interactions, the location of the critical end point has a non-trivial behaviour in the T −μ B plane, which differs from that in mean field calculations.
1 Introduction The phase diagram of Quantum Chromodynamics (QCD) is a widely studied topic by both experimental and theoretical physics and much has been learned about its properties since its first conjecture by N. Cabibbo and G. Parisi [1]. However, the phase structure at low temperatures and high baryonic a e-mail:
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density remains a mystery, e.g., the existence of a first order phase transition and the critical end point (CEP). Heavy ion collision (HIC) experiments conducted by the STAR Collaboration in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory [2–4] and by NA61/SHINE Collaboration in the Super Proton Synchrotron (SPS) at CERN [5,6], are currently, not only studying the properties of the quark-gluon plasma (QGP), but also trying to map the phase boundary of QCD. In the future, other facilities like the Nuclotron based Ion Collider fAcility (NICA) at Joint Institute for Nuclear Research [7], Facility for An
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