Understanding the Theory of Quantum Chromodynamics

Quantum chromodynamics is the part of quantum field theory that describes one of the fundamental forces, the strong interaction (interaction between quarks and gluons). In the early 1970s, it was proposed (as a theory) to understand the structure of baryons (collectives of 3 quarks, such as protons and neutrons) and mesons (quark-antiquark pairs, such as pions). This theory claims that the main aspect of the strong interaction is defined by a special symmetry between the color charges of the quarks.

The Greek word Chromos means “color”; this is the basis of the name chromodynamics. This name is appropriate since quark charges, basic particles within this theory, are designated as color charge, although it is not related to the visual perception of color. Quantum chromodynamics is a very important part of the standard model of particle physics. David Politzer, Frank Wilczek, and David Gross, who had proposed such a theory, were awarded the Nobel Prize in Physics in 2004 for their discovery.

To understand a little of what it is about, we are going to analyze the main characteristics of quantum chromodynamics:

• Asymptotic Freedom – One of the theory’s fundamental properties is asymptotic freedom: at short distances, charged particles are practically free. However, when the distance between them increases, the interaction that holds them together also increases. This is in stark contrast to the character of other interactions such as electromagnetic and gravitational, which decrease with distance. This anomalous behavior of quantum chromodynamics is because the mediators of the interaction (gluons) are capable of interacting with each other. This contrasts with the magnetic interaction, whose mediators, the photons, do not interact with each other.
• Color Charge Preservation – The Lagrangian of quantum chromodynamics has a SU (3) symmetry in the dependent part of the lepton fields. This implies by Noether’s theorem that there are conserved quantities associated with this symmetry. The conserved quantity is what we call “color.” The three varieties of colors are customarily designated as R (red), B (blue), and G (green) (although these colors have nothing to do with visual color, which is an electromagnetic phenomenon associated with different wavelengths).
• Color Charge Confinement – The confinement of the color charge occurs since gluons, in turn, can interact with each other according to their color charge. This contrasts with the situation of the photons of the electromagnetic field that, since they are devoid of charge, do not interact with each other. That crucial difference makes the electromagnetic interaction potentially infinite in range versus the very short range of the strong interaction.
• Gluon Field Equation – The gluonic field is made up of 8 types of gluons. Each of these eight types of gluons is given by a gluon field tensor formally similar to the electromagnetic field tensor. In total, the gluonic field has 128 scalar components (8 types of the gluon, with 16 components to each gluonic field).

Although this subject is extremely complex, it has served several things since quantum chromodynamics tries to predict the behavior of quarks and gluons. The prediction of these particles is so important that even a branch called quantum chromodynamics on lattice was born, which turns computers into laboratories that model the behavior of quarks and digital gluons. The birth of this concept allows us to understand the structure of matter better since predicting the behavior of particles helps us understand the nature of things since there are particles that this branch studies that are fundamental components of baryonic matter.

This concept has also helped us to understand the origin of the universe by understanding and trying to predict quarks and gluons. Also, remember that quantum chromodynamics is a fundamental part of the standard model of particle physics. That is why it is also essential for Higgs Boson’s experiments. Chromodynamics also helps in energy matters. As we explained before, it is a basis for particle physics, where many techniques allow us to make better solar panels and the use of different nuclear energies. This is why more research is being done on the subject to better manage atoms and particles.

In industrial matters, it was not far behind since many techniques used in particle physics help with the analysis of container goods in ports and airports. In addition to determining the composition of food, sterilizing materials for the food industry, analyzing proteins with pharmacological interest, and characterizing new manufacturing materials are among many other applications. Besides, these topics within particle physics have helped with the creation of instruments that are used in the diagnosis of diseases and also with the development of radiation therapies, among other things in the world of medicine.

Without a doubt, quantum chromodynamics is a very complicated subject that requires a lot of knowledge to be understood. However, it is a fundamental tool and is the axis of the standard model of particle physics. This is why its development was significant for the understanding of many physical phenomena and the structure of matter. This subject is still very young, and experiments and research will continue to be developed in the future that will reveal to us a better way in which to make a prediction of particles and their use in human life. It will also give us a better understanding of the universe in general, both its history and its effects, rules, and structure. If it is a topic that intrigues you and you want to know more, we recommend that you study particle physics.