A dense quark liquid is distinct from a dense nucleon liquid

Atomic nuclei are made up of nucleons (like protons and neutrons), which are themselves made up of quarks. When crushed at high densities, the nuclei dissolve into a liquid of nucleons, and at even higher densities, the nucleons themselves dissolve into a liquid of quarks.

In a new study, published in the journal Physical examination Bresearchers wondered whether nucleon and quark liquids were fundamentally different.

Their theoretical calculations suggest that these liquids are different. Both types of liquids produce vortices as they spin, but in quark liquids, the vortices carry a “color magnetic field,” similar to an ordinary magnetic field. Such an effect does not exist in nucleic liquids. Thus, these vortices clearly distinguish quark liquids from nuclear liquids.

Quarks and nucleons inside nuclei interact with each other via the strong nuclear force. This force has an intriguing property known as confinement. This means that scientists can only observe groups of quarks bonded together, but never an individual quark. In other words, quarks are said to be “confined”. It is also difficult to describe confinement, or even to define it precisely using theoretical tools.

This work, using the properties of vortices to distinguish quark liquids from nucleon liquids, addresses this long-standing problem. This suggests that there is a precise sense in which dense quark liquids are not confining while nuclear liquids are.

The question of whether nuclear matter is distinct from quark matter, that is, separated by a phase transition, is an old question in the study of strong interactions, particularly in the theory of chromodynamics. quantum (QCD). Likewise, scientists debate whether or not it is possible to give a precise definition of confinement.

Both of these questions have been explored in the past from a relatively old perspective, known as the Landau paradigm for phase transitions. Considerations of the Landau paradigm suggest that nuclear matter and quark matter are not distinct. This also implies that confinement cannot be clearly defined in the QCD.

This work challenges these conclusions by adopting a new set of tools discovered by physicists over the past 40 years. These tools detect topological transitions in materials that do not fit the old paradigm. Applied to the study of QCD, they reveal that quark matter and nuclear matter are distinct. To differentiate quark matter from nuclear matter, scientists must compare the properties of the vortices in the two cases. A simple calculation reveals that the vortex in quark matter traps a colored magnetic field absent in nuclear matter. This result also suggests that confinement can be rigorously defined in dense QCD.