Unified Field Theories ∗
نویسنده
چکیده
This article explains the idea of unified field theories in particle physics. It starts with a historical review of two successful theories which unified two apparently distinct forces: Maxwell’s theory of electromagnetism and Glashow–Salam–Weinberg theory of electroweak forces. Then it describes known four forces in Nature: gravitational, electromagnetic, weak and strong forces, and what their similarities and differences are. All of them are described based on the same principle (gauge principle), despite their distinct appearances due to their different phases of dynamics. Especially the last three forces are very similar to each other theoretically. Moreover, they seem to be intimately related to each other in order to guarantee the neutrality of matter (why the hydrogen atom is absolutely charge neutral) and seemingly miraculous anomaly cancellation in the electroweak theory which otherwise renders the quantum theory inconsistent. Grand Unified Theories (GUTs) are introduced to describe the last three forces as consequences of a single force, and explain the neutrality of matter and anomaly cancellation automatically. The original model is disfavored both from experimental and theoretical point of view. Experimentally, it predicts a lifetime of proton below experimental lower bound, and the pattern of measured gauge coupling constants does not follow its prediction. Theoretically, it predicts the energy scale of unification many orders of magnitudes larger than the scale of the weak force and makes the electroweak theory unstable against the radiative corrections. Supersymmetry is introduced to solve the latter problem. It makes the hierarchy in energy scales
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