Region of a hadron-quark mixed phase in hybrid stars

Abstract

Hadron-quark mixed phase is expected in a wide region of the inner structure of hybrid stars. However, we show that the hadron-quark mixed phase should be restricted to a narrower region to because of the charge screening effect. The narrow region of the mixed phase seems to explain physical phenomena of neutron stars such as the strong magnetic field and glitch phenomena, and it would give a new cooling curve for the neutron star. PACS numbers: Valid PACS appear hereIt is widely believed that there should be quark matter in the inner core region of neutron stars because the central density of neutron stars is sufficiently high for nucleons to dissolve into more elementary particles, namely quarks. Nowadays we consider that compact stars consist of not only nuclear matter but also other matter such as hyperons and quarks. We call such stars hybrid stars.Although deconfinement phase transition is still not clearly understood, many authors have studied the transition through modeling and first-principle calculations such as those of lattice QCD. Properties of quark matter have been actively studied theoretically in terms of quark-gluon plasma, color superconductivity [1, 2] and magnetism [3][4][5], and experimentally in terms of relativistic heavy-ion collisions [6] and early-universe and compact stars [7,8]. Such studies are continuing to provide exciting results [9].Because many theoretical calculations have suggested that deconfinement transition is of first order at low temperature and high density [10,11], we assume it to be a first-order phase transition here. The Gibbs condition (GC) [12] then gives rise to various structured mixed phases (SMPs). The SMPs suggested by Heiselberg et al. [13] and Glenndening and Pei [14] suggest a crystalline structure of the mixed phase in the core region of hybrid stars. Such structures are called "droplets", "rods", "slabs", "tubes", and "bubbles". These SMPs exist within a wide density range if we take a moderate value of the surface tension. However, if the surface effect is strong, the SMPs are limited to a narrow density region. On the other hand, Voskresensky et al. [15] reported the charge screening effect for several cases of droplets and slabs. They showed that even if we take a moderate value of the surface tension, SMPs cannot exist because of the charge screening effect. They referred to this phenomenon as mechanical instability. However, they used a linear approximation to solve the Poisson equation.We have presented the equation of state (EOS) for the mixed phase taking into account the charge screening effect [16] without recourse to any approximation. The * endo@t.kagawa-nct.ac.jp EOS is similar to that obtained from the Maxwell construction (MC). The allowed region of the mixed phase should then be narrow due to the charge screening effect.Recently "black stars" have been proposed by Barcelo et al. [17], who suggested that quantum effects prevent a star from collapsing into a "Black hall". Therefore, the EOS of hadron matter in the high-density states plays...

Surface tension of highly magnetized degenerate quark matter

“…In the case of mixed phases, it is known that there is a critical value for the surface tension of the order of tens of MeV / fm 2 [17][18][19][20] which determines two possible scenarios. If the surface tension is smaller than the critical value, a mixed phase is energetically favored; if it is larger, the hadron-quark interface in hybrid stars must be a sharp discontinuity.…”

Shear modulus of the hadron-quark mixed phase

“…We do not have to worry about such errors in our description of the quark blobs, since we are using an improved bag model for them. We also include the oft-neglected contribution from the surface tension to the pressure balance in a few of our EOSs, following [37][38][39][40].…”

Impact of Rotation on Quark–Hadron Hybrid Stars

“…We also adopt the EOS derived in a previous paper [9] and then apply it to the TOV equation [10,16]. For comparison, we perform a calculation for a stationary rotating star using our EOS.…”

“…We use our previous formulation [9,10], which we briefly review here. The quark phase consists of the lighter u, d, and s quarks, together with electrons.…”