Axion effects on quark matter and quark-matter cores in massive hybrid stars

Abstract

Using a three-flavor Nambu--Jona-Lasinio model to describe the charge-parity violating effects through axion field, we investigate the axion effects on quark matter and quark-matter cores in massive hybrid stars. The properties of quark matter vary with the scaled axion field $a/f_a$ in a periodic manner, with a period of $2\pi$. Within the range from 0 to $\pi$, axion field decrease the baryon chemical potential of the first-order phase transition, leading to an increase in normalized pressure and stiffening of the quark matter equation of state. The effect of axions on hybrid star matter that includes the hadron-quark phase transition is contrary to expectations. The axion field shifts the onset of the hadron-quark mixed phase to lower densities but slightly softens the equation of state of the mixed phase matter, which also results in a slight decrease in the maximum mass and corresponding radius of the hybrid stars. However, we also find that the lowering of the onset of the mixed phase significantly increases the radius and mass of the quark-matter core in the hybrid star. Therefore, our results indicate with axion effects, a sizable quark-matter core can appear in $2M_{\odot }$ massive neutron stars.

6 pages, 3 figures

References in corpus (20)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• The order of the quantum chromodynamics transition predicted by the standard model of particle physics
• GW190814: Gravitational Waves from the Coalescence of a 23 M${}_{\odot }$ Black Hole with a 2.6 M${}_{\odot }$ Compact Object
• PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star Matter
• A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation
• A NICER View of the Massive Pulsar PSR J0740+6620 Informed by Radio Timing and XMM-Newton Spectroscopy
• Locating the inner edge of neutron star crust using terrestrial nuclear laboratory data
• Correlated density-dependent chiral forces for infinite matter calculations within the Green's function approach
• Merger and post-merger of binary neutron stars with a quark-hadron crossover equation of state
• Plausible presence of new state in neutron stars with masses above $0.98M_{\mathrm{TOV}}$
• Multimessenger Constraints on Radiatively Decaying Axions from GW170817
• Thermal properties of asymmetric nuclear matter with an improved isospin- and momentum-dependent interaction
• First Constraints on the Photon Coupling of Axion-like Particles from Multimessenger Studies of the Neutron Star Merger GW170817
• Gamma-Ray Flashes from Dark Photons in Neutron Star Mergers
• Symmetry energy effects on the properties of hybrid stars
• Axion effects in the stability of hybrid stars
• Properties of quark matter and hybrid stars from a quasiparticle model
• In medium properties of axion within a Polyakov loop enhanced Nambu-Jona-Lasinio model
• Properties of quark-matter cores in massive hybrid stars
• Speed of sound and polytropic index in QCD matter