Colucci, G.

Sedrakian, A.

Sinha, M.

GSI Repository

Hypernuclear and strange quark matter in compact stars ∗A. Sedrakian, M. Sinha, and G. ColucciInstitut fu¨r Theoretische Physik, J. W. Goethe-Universita¨t Frankfurt am Main, GermanyWe have performed several studies of dense hypernu-clear matter under conditions relevant to neutron starswithin density dependent relativistic mean fields mod-els [1]. Our models include the full baryon octet. Onestudy was aimed at solving the so-called “hyperon puzzle”,i.e., the fact that the observation of two solar mass neu-tron star virtually excludes all the models of hypernuclearmatter proposed prior to this observation. We have stud-ied the sensitivity of the equation of state on the interac-tion between the baryon octet and the scalar mesons. Theallowed values of the hyperon-hyperon coupling via thescalar sigma meson was varied within a range admissibleby the symmetries and QCD sum rules. We have demon-strated that the equation of state of hypernuclear matter canbe stiffer in a certain range of parameters. This observationis a possible solution of the puzzle mentioned above. Thefinite temperature equation of state was studied under con-ditions when the neutrinos are trapped. It has been shownthat the neutrino trapping stiffens the equation of state.0 1 2 3 4ρ/ρ0050100150200250300P [MeV fm3 ]no trapped νYlep = 0.1Ylep = 0.40 1 2 3 4ρ/ρ0no trapped  νYlep = 0.1Ylep = 0.4Figure 1: Equation of state in the DD-ME2 parametrizationin presence of hyperons. Left panel: we fix the couplingconstant gΛΛσ = 0.58gNN σ from NSC89 potential and wevary the couplings for the Σ and Ξ hyperons. The dashedarea shows the variation of the EoS with the variation ofthe coupling constants of the remaining hyperons with thescalar meson. Right panel: the same as the left panel, butfor a fixed coupling constant gΣΣσ = 0.448gNNσ.Compact stars with strong magnetic fields (magnetars)have been observationally determined to have surface mag-netic fields of order of 1014 − 1015 G, the implied internal∗Work supported by the GSI-GU R&D project, HGS-HIRe and theAlexander von Humboldt Foundation.field strength being several orders larger. We have studiedthe equation of state and composition of dense hypernu-clear matter in strong magnetic fields in a range expectedin the interiors of magnetars [2]. We use the same modelas above, but with density independent coupling constants.One advantage of our study is that we have implementedrealistic density profiles of magnetic fields, which assumethat the field decreases from the center of the star andreaches asymptotically its value at the surface ∼ 1015 Gcharacteristic for magnetars. Thus, we have extended theprevious studies of hypernuclear matter to realistic situ-ation of density dependent field profiles and conducted astudy of parameter space that defines the shape of the fieldprofile. It should be noted that the previous studies over-estimated the effects of magnetic field on the matter at lowdensities, simply because of the constant field Ansatz.We have found that for sufficiently large fields Bc ≥1018 G the matter becomes unstable. The instability is as-sociated with the negative contribution of the field pressureto the baryonic and leptonic pressures in the direction par-allel to the magnetic field, which renders the total pressureof the system anisotropic. We have found that the onset ofinstability depends on the magnetic field profile (parame-terized in terms of two parameters) as well as on the cen-tral field value Bc. The instability sets in always for criti-cal central field values Bcr ≈ 1019 G for any values of theparameters. This gives a natural bound for the central mag-netic field of neutron stars with homogeneously distributedmagnetic field. We have shown also that the abundances ofbaryons are weakly affected by the magnetic field, whereasthose for the light leptons show de-Haas—van Alfven typeoscillations as a function of the magnetic field.Finally, we are conducting a study of strange quark mat-ter in strange stars which is exposed to large magneticfields [3]. The confinement feature is included via the phe-nomenological Richardson potential, which corresponds tostatic gluon exchange among the quarks. The model iscompared to the MIT model and differences between thesetwo confining models are discussed.References[1] G. Colucci and A. Sedrakian, Equation of state of hypernu-clear matter: impact of hyperon-scalar meson couplings. inpreparation.[2] M. Sinha, B. Mukhopadhyay, and A. Sedrakian, Hypernu-clear matter in strong magnetic field, Nuclear Physics A 898,43 (2013).[3] M. Sinha, X.-G. Huang, and A. Sedrakian Strange quark mat-ter within a confining model. in preparation.GSI SCIENTIFIC REPORT 2012 PHN-NQM-THEORY-13119

Hypernuclear and strange quark matter in compact stars

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Hypernuclear and strange quark matter in compact stars

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