Axial gauge resolves puzzle in calculations of hot and cold nuclear matter

Protons and neutrons are the building blocks of atomic nuclei, consisting of even smaller particles known as quarks and gluons. These particles interact through the strong force, one of the fundamental forces of nature. They form the nuclei found within every atom and can also create unique types of nuclear matter with exotic properties under extreme temperature and density conditions.

Scientists conduct experiments involving relativistic heavy ion collisions to investigate the characteristics of hot and cold nuclear matter. These experiments will continue to be carried out using the future Electron-Ion Collider. The primary objective is to comprehend how intricate forms of matter arise from elementary particles influenced by the strong force.

Theoretical calculations involving the strong force are intricate due to various approaches available for performing them, known as gauge choices. All gauge choices should yield identical outcomes for measurable quantities in experiments. However, the axial gauge, a specific choice, has perplexed scientists for a long time due to challenges in obtaining consistent results when using this gauge.

A recent study published in Physical Review Letters has successfully resolved this puzzle and opened up possibilities for reliable calculations of properties of hot and cold nuclear matter that can be validated in current and upcoming experiments.

The exotic form of nuclear matter studied in relativistic heavy ion collisions is referred to as the quark-gluon plasma (QGP). This type of matter existed in the early universe, and physicists explore its properties by recreating the incredibly high temperatures observed microseconds after the Big Bang through heavy ion collision experiments. By analyzing experimental data from these collisions and comparing them with theoretical calculations, physicists can determine various characteristics of the QGP. However, a calculation method known as the axial gauge previously led to the misconception that two properties describing the movement of heavy quarks within the QGP were identical.

Researchers from the Massachusetts Institute of Technology and the University of Washington have now discovered that this assumption is incorrect. Their study also carefully examined the specific conditions under which the axial gauge can be used and explained why the two properties are distinct. Furthermore, they demonstrated that two different methods for measuring the distribution of gluons, particles that transmit the strong force, inside nuclei should yield different results. This prediction will be tested at the future electron-ion collider.

Source: US Department of Energy

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