Explore the vast range of titles available.

We investigate the equilibrium structure and radial oscillations of strange quark stars admixed with fermionic dark matter. For strange quark matter, we employ a stiff equation of state from a color-superconductivity improved bag model. For dark matter, we adopt the cold free Fermi gas model. We rederive and numerically solve the radial oscillation equations of two-fluid stars based on general relativity, in which the dark matter and strange quark matter couple through gravity and oscillate with the same frequency. Our results show that the stellar maximum mass and radius are reduced by inclusion of dark matter. As to the fundamental mode of the radial oscillations, the frequency f0 is also reduced comparing to pure strange stars, and f02 reaches the zero point at the maximum stellar mass with dM/dϵq,c=0. Therefore, the stability criteria f02>0 and dM/dϵq,c>0 are consistent in our dark matter-mixed strange quark stars with a fixed fraction of dark matter. We also find a discontinuity of f0 as functions of the stellar mass, in contrast to the continuous function in pure strange stars. And it is also accompanied with discontinuity of the oscillation amplitudes as well as a discontinuous in-phase-to-out-phase transition between oscillations of dark matter and strange quark matter.

The nature of the F(R,T)-gravity in conjunction with the quark matter fluid (QMF) is examined in this research note. In the F(R,T)-gravity framework, we derive the equation of state for the QMF in the form of: F(R,T)=F1(R)+F2(T) and the model of F(R)-gravity. We also discuss how the quark matter supports the Ricci solitons with a conformal vector field in F(R,T)-gravity. In this continuing work, we give estimates for the pressure and quark density in the phantom barrier period and the radiation epoch, respectively. Additionally, we use Ricci solitons to identify several black hole prospects and energy requirements for quark matter fluid spacetime (QMF-spacetime) connected with F(R,T)-gravity. Furthermore, in the F(R,T)-gravity model connected with QMF, we also discuss some applications of the Penrose singularity theorem in terms of Ricci solitons with a conformal vector field. Finally, we deduce the Schrödinger Equation using the equation of state of the F(R,T)-gravity model connected with QMF, and we uncover some constraints that imply the existence of compact quark stars of the Ia-supernova type in the QMF-spacetime with F(R,T)-gravity.

The possible existence of stable up-down quark matter (udQM) was recently proposed, and it was shown that the properties of udQM stars are consistent with various pulsar observations. In this work we investigate the stability of udQM nuggets and found at certain size those objects are more stable than others if a large symmetry energy and a small surface tension were adopted. In such cases, a crust made of udQM nuggets exists in quark stars. A new family of white dwarfs comprised entirely of udQM nuggets and electrons were also obtained, where the maximum mass approaches to the Chandrasekhar limit.

Nontrivial topological gluon configuration is one of the remarkable features of the Quantum Chromodynamics (QCD). Due to chiral anomaly, the chiral imbalance between right- and left-hand quarks can be induced by the transition of the nontrivial gluon configurations between different vacuums. In this review, we will introduce the origin of the chiral chemical potential and its physical effects. These include: (1) the chiral imbalance in the presence of strong magnetic and related physical phenomena; (2) the influence of chiral chemical potential on the QCD phase structure; and (3) the effects of chiral chemical potential on quark stars. Moreover, we propose for the first time that quark stars are likely to be a natural laboratory for testing the destruction of strong interaction CP.

It is well known that the equation of state (EoS) of compact objects like neutron and quark stars is not determined despite there are several sophisticated models to describe it. From the electromagnetic observations, summarized in Lattimer and Prakash (2001), and the recent observation of gravitational waves from binary neutron star inspiral GW170817 Abbott et al. (2017) and GW190425 The LIGO Scientific Collaboration et al. (2020), it is possible to make an estimation of the range of masses and so constraint the mass of the neutron and quark stars, determining not only the best approximation for the EoS, but which kind of stars we would be observing. In this paper we explore several configurations of neutron stars assuming a simple polytropic equation of state, using a single layer model without crust. In particular, when the EoS depends on the mass rest density, p=Kρ0Γ, and when it depends on the energy density p=KρΓ, considerable differences in the mass-radius relationships are found. On the other hand, we also explore quark stars models using the MIT bag EoS for different values of the vacuum energy density B.

The integral parameters (mass, radius) of hot proto-quark stars that are formed in supernova explosion are studied. We use the MIT bag model to determine the pressure of up-down and strage quark matter at finite temperature and in the regime where neutrinos are trapped. It is shown that such stars are heated to temperatures of the order of tens of MeV. The maximum possible values of the central temperatures of these stars are determined. It is shown that the energy of neutrinos that are emitted from proto-quark stars is of the order of 250÷300 MeV. Once formed, the proto-quark stars cool by neutrino emission, which leads to a decrease in the mass of these stars by about 0.16–0.25 M⊙ for stars with the rest masses that are in the range Mb=1.22−1.62 M⊙.

In this paper, we investigated the thermodynamic properties of strange quark matter using the Nambu-Jona-Lasinio (NJL) model at finite temperatures where we considered the dynamical mass as the effective interaction between quarks. By considering the pressure of strange quark matter (SQM) at finite temperatures, we showed that the equation of state of this system gets stiffer with increasing temperature. In addition, we investigated the energy conditions and stability of the equation of state and showed that the equation of state of SQM satisfies the conditions of stability. Finally, we computed the structure properties of hot strange quark stars (SQS) including the gravitational mass, radius, Schwarzschild radius, average density, compactness, and gravitational redshift. Our calculations showed that in this model, the maximum mass and radius of SQS increase with increasing temperature. Furthermore it was shown that the average density of SQS is greater than the normal nuclear density, and it is an increasing function of temperature. We also discussed the temperature dependence of the maximum gravitational mass calculated by different methods.

A bstract We investigate a simple holographic model for cold and dense deconfined QCD matter consisting of three quark flavors. Varying the single free parameter of the model and utilizing a Chiral Effective Theory equation of state (EoS) for nuclear matter, we find four different compact star solutions: traditional neutron stars, strange quark stars, as well as two non-standard solutions we refer to as hybrid stars of the second and third kind (HS2 and HS3). The HS2s are composed of a nuclear matter core and a crust made of stable strange quark matter, while the HS3s have both a quark mantle and a nuclear crust on top of a nuclear matter core. For all types of stars constructed, we determine not only their mass-radius relations, but also tidal deformabilities, Love numbers, as well as moments of inertia and the mass distribution. We find that there exists a range of parameter values in our model, for which the novel hybrid stars have properties in very good agreement with all existing bounds on the stationary properties of compact stars. In particular, the tidal deformabilities of these solutions are smaller than those of ordinary neutron stars of the same mass, implying that they provide an excellent fit to the recent gravitational wave data GW170817 of LIGO and Virgo. The assumptions underlying the viability of the different star types, in particular those corresponding to absolutely stable quark matter, are finally discussed at some length.

Neutron stars and quark stars are not only characterized by their mass and radius but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star's internal structure and thus on unknown nuclear physics. We find universal relations between the moment of inertia, the Love number, and the quadrupole moment that are independent of the neutron and quark star's internal structure. These can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, distinguish neutron stars from quark stars, and test general relativity in a nuclear structure—independent fashion.

The influence of the dimensions on the f and p 1 pulsation modes from strange quark stars, in the Cowling approximation, are investigated. For that purpose, the d -dimensional nonradial pulsation equations ( d > 4) are numerically integrated considering that the Schwarzschild-Tangherlini line element describes the spacetime outside the object. We found that the fluid pulsation modes could become larger than those obtained in four dimensions. In four dimensions, the f pulsation mode is nearly constant, and for high total masses, it increases monotonically and quickly with the total mass. In this mass interval, the f frequencies grow for the spacetime dimensions between 4 and 6 and decay for d larger than 7. Concerning the p 1 pulsation modes, we found that they increase with the spacetime dimension and decline with the increment of the total mass.