Modern Elementary Particle Physics Explaining and Extending the Standard Model

The Standard Model of particle physics is an awesome theory, providing a description and explanation of the world we see, in a full relativistic quantum field theory. It leaves no puzzles in its domain. It achieves the goals of four centuries of physics. This book describes and explains the Standard Model to anyone who has had an introductory course in quantum theory.

Remarkably, the field of particle physics is completely different today from what it was before the 1970s. That's because there was huge progress in a few years around 1970, when some major experimental and theoretical developments occurred and merged together. Physicists learned that quarks and leptons are the fundamental objects of which all matter is composed; they interact via the exchange of “gauge bosons.” The forces that significantly affect them are the unified electroweak force, whose gauge bosons are the photon and the W± and Z0 bosons, and the strong force. The theory of the strong force is called quantum chromodynamics (QCD); the gauge bosons of the strong force are the (eight) gluons. (All the new terms here will be defined as the new physics appears in context.)

In another sense there is great continuity. The theory fully incorporates special relativity and quantum field theory. And there has been a continuous development of relativistic quantum field theory from its inception before 1930. Theorists have learned how to deal with difficult problems such as mass and renormalization. There has been steady and extraordinary progress in particle physics, both in understanding quantum field theory and in learning what to include in the Lagrangian; no revolution has occurred. The theories which describe the particles and their interactions seem to be “gauge theories,” a special class of quantum theories where there is an invariance principle that necessarily implies the existence of interactions mediated by gauge bosons. In gauge theories the interaction Lagrangian is, in a sense, inevitable rather than being introduced in an ad hoc way as in quantum theory.

The theory is formulated in terms of a function called “the Lagrangian.” In practice, “theory” and “Lagrangian” mean the same thing.

The basic formulation of the theory is accessible to anyone having a simple undergraduate introduction to quantum mechanics including spin.