Effect of in-medium hadron parameter modification on nuclear matter equation of state

Abstract

We investigate the effect on the nuclear matter equation of state ͑EOS͒ due to modification of meson and nucleon parameters in a nuclear medium as a consequence of the partial restoration of chiral symmetry. To get the EOS, we have used Brueckner-Bethe-Goldstone formalism with Bonn-B potential as a two-body interaction and QCD sum rule and Brown-Rho scaling prescriptions for modification of hadron parameters. We find that the EOS is very much sensitive to the meson parameters. We can fit, with the two-body interaction alone, both the saturation density and the binding energy per nucleon. PACS number͑s͒: 21.65.ϩf, 12.38.Aw It is becoming more and more clear now that the chiral symmetry of the QCD Lagrangian and its spontaneous breaking ͓1͔ play a very important role in determining the structure of low mass hadrons which are comprised of u, d, and s quarks, and instantons play a crucial role in hadron correlators in mediating the spontaneous chiral symmetry breaking ͓2,3͔. Physical confinement of quarks seems to play a lesser role. The spontaneous breaking of the chiral symmetry is signaled by the nonvanishing values in the physical vacuum of the quark and gluon condensates ͓4-6͔. Calculations based on chiral perturbation theory and the QCD sum rule ͑QSR͒ indicate that values of these condensates are reduced when the hadrons are put in a medium, hence giving rise to partial restoration of chiral symmetry ͓7,8͔. Thus, there is a lot of interest nowadays to understand the mechanism of partial restoration in the nuclear medium of the chiral symmetry of the QCD Lagrangian ͓9,10͔, and to isolate effects arising out of it, as it provides a handle to understand nonperturbative QCD phenomena. The most important consequence of chiral symmetry restoration has been identified as modification of hadron properties in nuclear matter ͓11,12͔. Experimental evidence towards this is believed to be a large excess of e ϩ e Ϫ pairs observed in the invariant mass region around 400 MeV in the 200A GeV central collisions of S on Au and W by CERES ͓13͔ and HELIOS ͓14͔ groups, respectively. This has been explained ͓11,15͔ by arguing that the rho meson mass in nuclear matter is reduced at the densities created in the collision. Theoretical studies towards this were triggered after pointing out by Brown and Rho ͓16͔, based on the restoration of scale invariance of QCD, that masses of hadrons would scale in nuclear medium aswhere the density dependent quantities are denoted by asterisks. m N , m V , and m denote the masses of nucleon, vector mesons ͑rho, omega͒, and sigma mesons, respectively. f * is the in-medium pion decay constant, which is expected to vanish at high density when chiral symmetry is completely restored. Therefore, the masses in Eq. ͑1͒ should decrease with increasing density. Quantitative estimations of the dependence of masses of hadrons with respect to density have been made in the quark meson coupling ͑QMC͒ model ͓17͔ and using the QSR approach ͓18͔. In both of these two approaches the behavior of vector meson mass var...

Deconfinement phase transition in hybrid neutron stars from the Brueckner theory with three-body forces and a quark model with chiral mass scaling

“…In the quark sector, we adopted the semiphenomenological CDDM quark model, which exhibits a confinement mechanism alternative to the crude MIT bag model. Furthermore, in contrast with the extension of the MIT model, where the density dependence is introduced artificially [52], CDDM quark model shapes its density dependence in agreement with chiral requirements [15,16].…”

“…The chemical potentials µ u , µ d , µ s , and µ e can then be calculated by Eqs. (13) and (15). Therefore, the energy density of the quark matter is a function of the baryon number density n and the charge density Q q , i.e., E q = E q (n, Q q ) or…”

“…Effective masses of hadrons and quarks have been extensively discussed, e.g., within the Nambu-Jona-Lasinio model [13] and within a quasi-particle model [14]. In principle, the density dependence of quark masses should be connected to the in-medium chiral condensates [15,16].…”

Short-range effects on nuclear pairing

“…It appears experimentally supported by the quenching of the ρ meson mass in dilepton production in heavy ion collisions [6]. The theoretical treatment [11] can only be accomplished using an interaction explicitly dependent on the meson parameters. For this reason we use the Bonn-B potential [12] and only investigate the effect of the ω meson mass, whose strength is by far the largest one.…”

Chiral Condensates in Quark and Nuclear Matter

“…It is expected that this broken symmetry would be restored in a medium, and several signals have recently been suggested for its manifestation in nuclear matter, such as the spectral enhancement near the 2M π (M π is the pion mass) threshold [2], the systematic appearance of the parity doublets in the missing-states region [3], and the vector manifestation [4] etc. It is also shown that the partial restoration of chiral symmetry has strong effects on the nuclear saturation [5] and the nuclear equation of state [6].…”