Strangeon and Strangeon Star

Abstract

Abstract. The nature of pulsar-like compact stars is essentially a central question of the fundamental strong interaction (explained in quantum chromo-dynamics) at low energy scale, the solution of which still remains a challenge though tremendous efforts have been tried. This kind of compact objects could actually be strange quark stars if strange quark matter in bulk may constitute the true ground state of the strong-interaction matter rather than 56 Fe (the so-called Witten's conjecture). From astrophysical points of view, however, it is proposed that strange cluster matter could be absolutely stable and thus those compact stars could be strange cluster stars in fact. This proposal could be regarded as a general Witten's conjecture: strange matter in bulk could be absolutely stable, in which quarks are either free (for strange quark matter) or localized (for strange cluster matter). Strange cluster with three-light-flavor symmetry is renamed strangeon, being coined by combining "strange nucleon" for the sake of simplicity. A strangeon star can then be thought as a 3-flavored gigantic nucleus, and strangeons are its constituent as an analogy of nucleons which are the constituent of a normal (micro) nucleus. The observational consequences of strangeon stars show that different manifestations of pulsarlike compact stars could be understood in the regime of strangeon stars, and we are expecting more evidence for strangeon star by advanced facilities (e.g., FAST, SKA, and eXTP). Introduction: What is a strangeon?The baryonic matter in the Universe is well described by the Standard Model of particle physics. Six flavors of quarks are fundamental Fermions that constitute baryonic matter, among which up (u), down (d) and strange (s) quarks are light flavors (the other heavy flavors: c, t, b). Atomic nucleus, the most familiar baryonic matter to us, is composed of nucleons which is further composed of only two favors of constituent quarks, i.e. u and d quarks. In other words, the nucleon is the constituent of a 2-flavored micro-nucleus. Similarly, the "strangeon" we are explaining in this contribution is the constituent of a 3-flavored macro-nucleus, and is simply an abbreviation of "strange nucleon" (with strangeness degree of freedom there).The existence of 3-flavored nuclei might be superficially understood by analysis of energy scale. Quarks are often described by mass parameters that are measured indirectly since they are confined inside hadrons rather than free particles, and the mass parameters are the key parameters to make a judgment on the quark-flavor degrees of freedom at a certain energy scale. The current mass of both u and d quarks are only a few MeV while that of s quark is around 100 MeV. For nuclei or nuclear matter with baryon density n 0 ≃ 0.16 fm −3 , the separation between quarks is ∆x ∼ 0.5 fm, and the energy scale is then in the order of E nucl ∼ 400 MeV according

Differentially rotating strange star in general relativity

“…In this work, B is chosen to be (138 MeV) 4 . Another EoS model considered in this work is the so-called strangeon star model [43]. Unlike the MIT bag model in which quarks are assumed to be de-confined and described by Fermi gas approximation, Lai and Xu suggested that clustering of quarks is possible at the density of a cold compact star since the coupling of strong interaction is not negligible at such energy scale.…”

Uniformly rotating, axisymmetric, and triaxial quark stars in general relativity

“…1 Such a quark-cluster star has also been named a strangeon star in Ref. [69]. Lai and Xu attempted to approach the EOS of such quarkcluster star with phenomenological models, i.e., to compare the intercluster potential with the interaction between inert molecules (a similar approach has also been discussed in [70]).…”