scholarly journals Two Novel Approaches to the Hadron-Quark Mixed Phase in Compact Stars

Universe ◽  
2018 ◽  
Vol 4 (9) ◽  
pp. 94 ◽  
Author(s):  
Vahagn Abgaryan ◽  
David Alvarez-Castillo ◽  
Alexander Ayriyan ◽  
David Blaschke ◽  
Hovik Grigorian

First-order phase transitions, such as the liquid-gas transition, proceed via formation of structures, such as bubbles and droplets. In strongly interacting compact star matter, at the crust-core transition but also the hadron-quark transition in the core, these structures form different shapes dubbed “pasta phases”. We describe two methods to obtain one-parameter families of hybrid equations of state (EoS) substituting the Maxwell construction that mimic the thermodynamic behaviour of pasta phase in between a low-density hadron and a high-density quark matter phase without explicitly computing geometrical structures. Both methods reproduce the Maxwell construction as a limiting case. The first method replaces the behaviour of pressure against chemical potential in a finite region around the critical pressure of the Maxwell construction by a polynomial interpolation. The second method uses extrapolations of the hadronic and quark matter EoS beyond the Maxwell point to define a mixing of both with weight functions bounded by finite limits around the Maxwell point. We apply both methods to the case of a hybrid EoS with a strong first order transition that entails the formation of a third family of compact stars and the corresponding mass twin phenomenon. For both models, we investigate the robustness of this phenomenon against variation of the single parameter: the pressure increment at the critical chemical potential that quantifies the deviation from the Maxwell construction. We also show sets of results for compact star observables other than mass and radius, namely the moment of inertia and the baryon mass.

Universe ◽  
2019 ◽  
Vol 5 (7) ◽  
pp. 174
Author(s):  
János Takátsy ◽  
Péter Kovács ◽  
Zsolt Szép ◽  
György Wolf

The equation of state provided by effective models of strongly interacting matter should comply with the restrictions imposed by current astrophysical observations of compact stars. Using the equation of state given by the (axial-)vector meson extended linear sigma model, we determine the mass–radius relation and study whether these restrictions are satisfied under the assumption that most of the star is filled with quark matter. We also compare the mass–radius sequence with those given by the equations of state of somewhat simpler models.


2021 ◽  
Vol 252 ◽  
pp. 06001
Author(s):  
Themistoklis Deloudis ◽  
Polychronis Koliogiannis ◽  
Charalampos Moustakidis

In agreement with the gravitational-wave events which are constantly increasing, new aspects of the internal structure of compact stars have come to light. A scenario in which a first order transition takes place inside these stars is of particular interest as it can lead, under conditions, to a third gravitationally stable branch (besides white dwarfs and neutron stars). This is known as the twin star scenario. The new branch yields stars with the same mass as normal compact stars but quite different radii. In the current work, we focus on hybrid stars undergone a hadron to quark phase transition near their core and how this new stable configuration arises. Emphasis is to be given especially in the aspects of the phase transition and its parametrization in two different ways, namely with Maxwell construction and with Gibbs construction. Qualitative findings of mass-radius relations of these stars will also be presented.


2000 ◽  
Vol 177 ◽  
pp. 603-604 ◽  
Author(s):  
Hovik Grigorian ◽  
Gevorg Poghosyan ◽  
Edvard Chubarian ◽  
David Blaschke

AbstractThe occurence of a quark matter core in rotating compact stars has been investigated within general relativity as a function of both the rotational frequency and the total baryon number. We demonstrate that the deviation of the braking index fromn= 3 signals not only the occurence but also the size of a quark matter core in a pulsar. We suggest that in systems with mass accretion onto a rapidly rotating compact star a spin-down to spin-up transition might signal a deconfinement transition in its interior.


Universe ◽  
2019 ◽  
Vol 5 (2) ◽  
pp. 61 ◽  
Author(s):  
Alexander Ayriyan ◽  
David Alvarez-Castillo ◽  
David Blaschke ◽  
Hovik Grigorian

We develop a Bayesian analysis method for selecting the most probable equation of state under a set of constraints from compact star physics, which now include the tidal deformability from GW170817. We apply this method for the first time to a two-parameter family of hybrid equations of state that is based on realistic models for the hadronic phase (KVORcut02) and the quark matter phase (SFM α ) which produce a third family of hybrid stars in the mass–radius diagram. One parameter ( α ) characterizes the screening of the string tension in the string-flip model of quark matter while the other ( Δ P ) belongs to the mixed phase construction that mimics the thermodynamics of pasta phases and includes the Maxwell construction as a limiting case for Δ P = 0 . We present the corresponding results for compact star properties like mass, radius and tidal deformabilities and use empirical data for them in the newly developed Bayesian analysis method to obtain the probabilities for the model parameters within their considered range.


2017 ◽  
Vol 32 (10) ◽  
pp. 1750055 ◽  
Author(s):  
Koushik Chakraborty ◽  
Farook Rahaman ◽  
Arkopriya Mallick

We propose a relativistic model of compact star admitting conformal symmetry. Quark matter and baryonic matter which are considered as two different fluids, constitute the star. We define interaction equations between the normal baryonic matter and the quark matter and study the physical situations for repulsive, attractive and zero interaction between the constituent matters. The measured value of the Bag constant is used to explore the spacetime geometry inside the star. From the observed values of the masses of some compact objects, we have obtained theoretical values of the radii. Theoretical values of the radii match well with the previous predictions for such compact objects.


2017 ◽  
Vol 26 (01n02) ◽  
pp. 1740012
Author(s):  
Che Ming Ko ◽  
Feng Li

For quark matter at finite baryon chemical potential, its density develops large fluctuations when it undergoes a first-order phase transition. Based on the Nambu–Jona–Lasinio (NJL) model, we have used the linear response theory to study the growth rate of density fluctuations and its dependence on the wavelength of unstable modes. Using the transport equation derived from the NJL model, we have also studied the time evolution of the unstable modes and the density fluctuations in a baryon-rich quark matter that is confined in a finite volume. Allowing the expansion of the quark matter, we have further studied the survivability of the density fluctuations as the density and temperature of the quark matter decrease. Possible experimental signatures of the density fluctuations have been suggested.


2018 ◽  
Vol 191 ◽  
pp. 05015 ◽  
Author(s):  
Tamaz Khunjua ◽  
Konstantin Klimenko ◽  
Roman Zhokhov

Isospin asymmetry is the well-known property of dense quark matter, which exists in the compact stars and is produced in heavy ion collisions. On the other hand, the chiral imbalance between left- and right- handed quarks is another highly anticipated phenomenon that could occur in the dense quark matter. To investigate quark matter under these conditions, we take into account baryon – μB, isospin – μI and chiral isospin – μI5 chemical potentials and study QCD phase portrait using NJL4 model generalized to two massive quarks that could condense into the pion condensation. We have shown that the chiral isospin chemical potential μI5 generates pion condensation in isospin asymmetric quark matter. Also, we have investigated discrete symmetry (duality) between chiral and pion condensates in the case of massless quarks, which stay relatively instructive even if the quarks have bare mass. To describe hot dense quark matter, in addition to the above-mentioned chemical potentials, we introduce non-zero temperatures into consideration.


2010 ◽  
Vol 19 (08n10) ◽  
pp. 1521-1524 ◽  
Author(s):  
J. G. COELHO ◽  
C. H. LENZI ◽  
M. MALHEIRO ◽  
R. M. MARINHO ◽  
M. FIOLHAIS

We investigate the hadron-quark phase transition inside neutron stars and obtain mass–radius relations for hybrid stars. The equation of state for the quark phase using the standard NJL model is too soft, leading to an unstable star and suggesting a modification of the NJL model by introducing a momentum cutoff dependent on the chemical potential. However, even in this approach, the instability remains. In order to remedy the instability we suggest the introduction of a vector coupling in the NJL model, which makes the EoS stiffer, reducing the instability. We conclude that the possible existence of quark matter inside the stars require high densities, leading to very compact stars.


2020 ◽  
Vol 229 (22-23) ◽  
pp. 3629-3649
Author(s):  
Konstantin Otto ◽  
Micaela Oertel ◽  
Bernd-Jochen Schaefer

AbstractNonperturbative equations of state (EoSs) for two and three quark flavors are constructed with the functional renormalization group (FRG) within a quark-meson model truncation augmented by vector mesons for low temperature and high density. Based on previous FRG studies without repulsive vector meson interactions the influence of isoscalar vector ω- and ϕ-mesons on the dynamical fluctuations of quarks and (pseudo)scalar mesons is investigated. The grand potential as well as vector meson condensates are evaluated as a function of quark chemical potential and the quark matter EoS in β-equilibrium is applied to neutron star (NS) physics. The tidal deformability and mass-radius relations for hybrid stars from combined hadronic and quark matter EoSs are compared for different vector couplings. We observe a significant impact of the vector mesons on the quark matter EoS such that the resulting EoS is sufficiently stiff to support two-solar-mass neutron stars.


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