Quantum Field Theory

Table of Contents

Quantum Field Theory, a collection of three theories, provides the equations governing the interaction among the fields, particles, and forces of the Standard Model:
- Quantum Electrodynamics (QED)
- Electroweak Theory (EWT)
- Quantum Chromodynamics (QCD)
QFT incorporates Quantum Mechanics, Special Relativity, and Classical Field Theory.
- Quantum Mechanics describes the behavior of tiny particles
- Adding Classical Field Theory allows for the creation and annihilation of particles, which QM alone does not.
- Adding Special Relativity allows for antiparticles, which QM alone does not.

QED governs the Electromagnetic Interaction, i.e. interactions among electrically charged particles, mediated by photons
The theory was developed independently in the late 1940s by Richard P. Feynman, Julian S. Schwinger, and Tomonaga Shin’ichirō,
From the Britannica
- “The electric and magnetic fields described in Maxwell’s equations are quantized, and photons appear as excitations of those quantized fields. In QED, photons serve as carriers of electric and magnetic forces. For example, two identical charged particles electrically repel one another because they are exchanging what are called virtual photons.
- Though the mathematical complexities of QED are formidable, it is a highly successful theory that has now withstood decades of precise experimental tests.”

The Electroweak Theory governs the Weak Interaction as well as the Electromagnetic Interaction. The Exchange Particles of the Weak Interaction are the W⁺, W^– and Z Bosons
The existence of the exchange particles, the neutral Z particles and the charged W particles, was verified experimentally in 1983 in high-energy proton-antiproton collisions at CERN.
The theory was developed independently in 1960s by Sheldon Lee Glashow, Abdus Salam, and Steven Weinberg

QCD governs the Strong Interaction, which takes place by exchanging Gluons.
The Strong Interaction acts only on particles with color-charge, that is, quarks and particles built from quarks, such as protons and neutrons.
The color-charges (red, green, and blue) are comparable to positive and negative electric charge: particles with opposite colors attract and particles with the same colors repel.
The theory was developed in 1973 by Harald Fritzsch, Heinrich Leutwyler, and Murray Gell-Mann.