On-shell versus curvature mass parameter fixing schemes in the quark-meson model and its phase diagrams

Abstract

We compute and compare the effective potential and phase structure for the quark-meson model in an extended mean-field approximation (e-MFA) when vacuum one loop quark fluctuations are included and the model parameters are fixed using different renormalization prescriptions.When the quark one loop vacuum divergence is regularized under the minimal subtraction scheme,the model setting of the parameter fixing using the curvature masses of the scalar and pseudo-scalar mesons, has been termed as the quark-meson model with the vacuum term(QMVT).However,this prescription becomes inconsistent when we notice that the curvature mass is akin to defining the meson mass by the self-energy evaluation at vanishing momentum.In this work,we apply the recently reported exact prescription of the on-shell parameter fixing,to that version of quark-meson (QM) model where the two quark flavors are coupled to the eight mesons of the $ SU(2)_{L} \times SU(2)_{R} $ linear sigma model with iso-singlet $ \sigma $ ($\eta$),iso-triplet $ \vec{a_{0}} $ ($ \vec{\pi} $) scalar(pseudo-scalar) mesons.The model then becomes, the renormalized quark-meson (RQM) model where physical (pole) masses of mesons and pion decay constant, are put into the relation of the running mass parameter and couplings by using the on-shell and the minimal subtraction renormalization schemes.The vacuum effective potential plots,the phase diagrams and the order parameter temperature variations for both the RQM model and QMVT model,are exactly identical for the $m_\sigma=$616 MeV.The effective potential is deepest in the QMVT model for $m_\sigma < $ 616 MeV and it becomes deepest in the RQM model when $m_\sigma > $616 MeV.