Defining Group Multiplication in Particle Physics

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SUMMARY

The discussion focuses on defining group multiplication in particle physics, specifically addressing the direct product of Lie groups such as U(1), SU(2), and SU(3). It clarifies that the notation G x H represents the direct product of two groups, where G and H are sets of pairs (g, h) with a defined binary operation. Additionally, the direct sum notation \bigoplus_{i=1}^n G_i is explained as the Cartesian product of groups with a specific group structure. This foundational understanding is crucial for advanced studies in particle physics.

PREREQUISITES
  • Understanding of Lie groups, specifically U(1), SU(2), and SU(3).
  • Familiarity with group theory concepts such as direct products and direct sums.
  • Knowledge of binary operations in group structures.
  • Basic comprehension of Cartesian products in mathematics.
NEXT STEPS
  • Research the properties of Lie groups and their applications in particle physics.
  • Study the implications of direct products and direct sums in group theory.
  • Explore advanced topics in group theory, such as representation theory.
  • Examine the role of group theory in the Standard Model of particle physics.
USEFUL FOR

Particle physicists, mathematicians specializing in group theory, and students studying the mathematical foundations of quantum mechanics will benefit from this discussion.

quantumfireball
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Everyone must be familiar with U(1),SU(2) and SU(3) Lie groups in particle physics .
But how does one define the multiplication of two groups of different dimensions
aka SU(2) X U(1) or SU(3) X SU(2) X U(1).
 
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You aren't multiplying them. That is the direct product of the groups. Give two groups the direct product GxH is the set of all pairs (g,h) g in G, h in H with the natural composition

(g,h)(g',h')=(gg',hh')
 
It's also the direct sum. If ever you encounter the notation [tex]\bigoplus_{i=1}^n G_i[/tex], this is what it means. Take the cartesian product of the G_i and give them a group structure by defining the binary operation as in matt grime's post. (g1,...,gn)(g1',...,gn'1)=(g1g1',...,gngn')
 
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