Examination of strangeness instabilities and effects of strange meson couplings in dense strange hadronic matter and compact stars

Abstract

International audienceBackground : The emergence of hyperon degrees of freedom in neutron star matter has been associated to first order phase transitions in some phenomenological models, but conclusions on the possible physical existence of an instability in the strangeness sector are strongly model dependent. Purpose : The purpose of the present study is to assess whether strangeness instabilities are related to specific values of the largely unconstrained hyperon interactions, and to study the effect of the strange meson couplings on phenomenological properties of neutron stars and supernova matter, once these latter are fixed to fulfill the constraints imposed by hypernuclear data. Method : We consider a phenomenological RMF model sufficiently simple to allow a complete exploration of the parameter space. Results : We show that no instability at supersaturation density exists for the RMF model, as long as the parameter space is constrained by basic physical requirements. This is at variance with a non-relativistic functional, with a functional behavior fitted through ab-initio calculations. Once the study is extended to include the full octet, we show that the parameter space allows reasonable radii for canonical neutron stars as well as massive stars above two-solar mass, together with an important strangeness content of the order of 30\%, slightly decreasing with increasing entropy, even in the absence of a strangeness driven phase transition. Conclusions : We conclude that the hyperon content of neutron stars and supernova matter cannot be established with present constraints, and is essentially governed by the unconstrained coupling to the strange isoscalar meson

Constraining Strangeness in Dense Matter with GW170817

“…For an equal mass binary where M 1 = M 2 = 1.6 M ⊙ , from Equation 17 we haveλ = λ 1 = λ 2 . As shown in Figure 6, we find the curves for nucleonic (set 1), hyperonic (set 2) and most Maxwell constructions (sets 7,9) essentially overlap, as the mass of the system lies only slightly above the critical one for set 2 (only a few hyperons populate the star), and below the critical mass for the appearance of quarks for these parameterizations. However, for the Gibbs construction (sets 3-5) and set 6 with Maxwell, quarks are present in the core of stars starting at much lower densities.…”

“…It is predicted that exotic degrees of freedom can also populate these objects, and that even the dissolution of baryons into their quark constituents through a phase transition to quark matter could be facilitated in such extreme environments. The impact of exotic compositions on the structure of isolated neutron stars has been studied in the past for stars composed of hyperons [1][2][3][4][5][6][7][8][9], Delta baryon resonances [10][11][12][13][14], meson condensates [15][16][17][18][19][20][21], quarks or even color superconducting quark matter [22][23][24][25][26]. Such degrees of freedom are usually associated with a softening of the equation of state (EoS), impacting the maximum mass and stability of stars [27,28].…”

Many-body Forces in Magnetic Neutron Stars

“…In particular, it has been extensively discussed in the literature whether exotic degrees of freedom might populate the core of neutron stars. On the one hand, it is more energetically favorable for the system to populate new degrees of freedom, such as hyperons (Dexheimer & Schramm 2008;Ishizuka et al 2008;Bednarek et al 2012;Fukukawa et al 2015;Gomes et al 2015;Maslov et al 2015;Oertel et al 2015;Lonardoni et al 2015Lonardoni et al , 2016; Biswal et al 2016;Burgio & Zappalà 2016;Chatterjee & Vidana 2016;Mishra et al 2016;Vidaña 2016;Yamamoto et al 2016;Tolos et al 2017); Torres et al 2017), delta isobars (Fong et al 2010;Schurhoff et al 2010;Drago et al 2014;Cai et al 2015;Zhu et al 2016), and meson condensates (Ellis et al 1995;Menezes et al 2005;Takahashi 2007;Ohnishi et al 2009;Alford et al 2010;Fernandez et al 2010;Mesquita et al 2010;Mishra et al 2010;Lim et al 2014;Muto et al 2015), in order to lower its Fermi energy (starting at about two times the saturation density). On the other hand, the EoS softening due to the appearance of exotica might turn some nuclear models incompatible with observational data, in particular with the recently measured massive neutron stars.…”

Color superconductivity in compact stellar hybrid configurations

“…The GM1 parametrization has been widely used for the description of nuclear matter in neutron stars (see for example [79,80] and references therein), however its continued utility may be questionable in light of recent constraints placed on the slope of the isospin asymmetry energy and neutron star radii.…”