Abstract
In this review, we discuss the physical characteristics of the magnetic dual chiral density wave (MDCDW) phase of dense quark matter and argue why it is a promising candidate for the interior matter phase of neutron stars. The MDCDW condensate occurs in the presence of a magnetic field. It is a single-modulated chiral density wave characterized by two dynamically generated parameters: the fermion quasiparticle mass m and the condensate spatial modulation q. The lowest-Landau-level quasiparticle modes in the MDCDW system are asymmetric about the zero energy, a fact that leads to the topological properties and anomalous electric transport exhibited by this phase. The topology makes the MDCDW phase robust against thermal phonon fluctuations, and as such, it does not display the Landau–Peierls instability, a staple feature of single-modulated inhomogeneous chiral condensates in three dimensions. The topology is also reflected in the presence of the electromagnetic chiral anomaly in the effective action and in the formation of hybridized propagating modes known as axion-polaritons. Taking into account that one of the axion-polaritons of this quark phase is gapped, we argue how incident γ-ray photons can be converted into gapped axion-polaritons in the interior of a magnetar star in the MDCDW phase leading the star to collapse, a phenomenon that can serve to explain the so-called missing pulsar problem in the galactic center.
Highlights
A fundamental question in nuclear physics/astrophysics currently is what is the state of matter that is realized in the interior of neutron stars (NS)
We reviewed the main physical characteristics of the magnetic dual chiral density wave (MDCDW) phase of dense quark matter and its possible connection with the astrophysics of NSs
One main attribute of this phase is its nontrivial topology, which is due to the combined effect of the density wave ground state and the dimensional reduction produced by the magnetic field on the Landau level (LLL), which together give rise to an asymmetric spectrum for the LLL
Summary
A fundamental question in nuclear physics/astrophysics currently is what is the state of matter that is realized in the interior of neutron stars (NS). Various QCD effective model studies, as well as QCD calculations in the large-Nc limit indicate that spatially inhomogeneous chiral phases, characterized by particle–hole pairs that carry total momentum, can be formed at relatively low temperatures and intermediate densities [50,51,52,53,54,55,56,57,58,59,60,61,62,63]. An additional effect that makes the MDCDW phase a viable candidate for the NS’s inner state of matter is that it is not washed out by thermal fluctuations at low temperatures This property is significant because even though single-modulated chiral condensates are energetically favored over their homogeneous counterpart at increasing densities and favored even over higher-dimensional modulations in three dimensions, the long-order range in single-modulated condensates is always washed out by the thermal fluctuations of the Goldstone bosons at arbitrarily small temperatures.
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