The matter inside a neutron star can take different forms: nucleon-dense liquid or quark-dense liquid. The latest research has found that in neutron stars, the quark liquid is essentially different from the nucleon liquid, as evidenced by the unique color magnetic field in its vortex. This discovery challenges previous views of quantum chromodynamics and provides new insights into the nature of binding.
Neutron star matter science
Atomic nuclei are composed of nucleons (such as protons and neutrons), which themselves are composed of quarks. When atomic nuclei are shattered at high densities, they dissolve into nucleon liquid, and at higher densities, the nucleons themselves dissolve into quark liquid. In this study, researchers explored the question of whether nucleonic liquids and quark liquids are fundamentally different. Their theoretical calculations showed that these liquids are different. Both liquids create vortices as they spin, but in quark liquids, the vortices carry a "colored magnetic field" that is similar to an ordinary magnetic field. In nuclear liquids there is no such effect. These vortices therefore make quark liquids very different from nucleon liquids.
The influence of quark liquids and nucleonic liquids
Quarks and nucleons in the nucleus interact through the strong nuclear force. This force has an interesting property called "constraint". This means that scientists can only observe groups of quarks bound together, not individual quarks. In other words, quarks are said to be "bound." It is also difficult to describe or precisely define "binding" using theoretical tools. This study solves this long-standing problem by using vortex properties to distinguish between quark liquids and nucleonic liquids. It shows that, in a precise sense, dense quark liquids are not bound, whereas nucleonic liquids are bound.
Challenging traditional theories
Whether nuclear matter is different from quark matter, in other words, whether there is a phase transition, is an old question in the study of strong interactions, especially in quantum chromodynamics (QCD) theory. Likewise, scientists have raised the question of whether it is possible to provide a clear definition for confinement. In the past, these two questions have been approached from a relatively old perspective known as the Landau paradigm of phase transitions. The Landau paradigm holds that nuclear matter and quark matter are not completely different. This also means that constraints cannot be explicitly defined in QCD.
This study challenges these conclusions by employing a new set of tools that physicists have discovered over the past 40 years. These tools can detect topological transitions in materials that do not fit previous paradigms. When applied to QCD studies, they reveal that quark matter and nuclear matter are distinct. To distinguish between quark matter and nuclear matter, scientists must compare the properties of the vortices in the two cases. Simple calculations show that the vortices in quark matter trap chromatic fields that are not present in nuclear matter. This result also shows that confinement can be rigorously defined in dense QCD.
References
"Higgs-constrained phase transitions for fundamental characterizations of matter", author: Alexei Chelman, Theodore Jacobson, Srimoi Sen and Lawrence G. Yaff, November 24, 2020, "Physical Review D".
DOI:10.1103/PhysRevD.102.105021
"Vortices carry magnetic flux in spin-0 superfluids," by Aleksey Cherman, Theodore Jacobson, Srimoyee Sen, and Laurence G. Yaffe, January 5, 2023, "Physical Reviews B".
DOI:10.1103/PhysRevB.107.024502
This research was supported by the U.S. Department of Energy's Office of Science, Office of Nuclear Physics, and its Quantum Horizons Program.
Compiled source: ScitechDaily