Calculating an expression for trace of generators of two Lie algebra

In summary, the conversation discusses the generators of a Lie algebra associated with SU(N) and an Abelian group, where the Q's are traceless and the P's are symmetric. The relation between the generators is given by [Q^a,P^b] = if^c_{ab}P^c, and the question is raised about the trace of [Q^a,P^b]Q^c P^d. It is suggested that this trace may not equal zero, as shown by the Poincaré algebra. The cyclic property of trace is also discussed, with the conclusion that tr[A,B] = 0 for any matrices, but tr([A,B]C) = 0 only for symmetric matrices.
  • #1
vnikoofard
12
0
Suppose we have
$$[Q^a,Q^b]=if^c_{ab}Q^c$$

where Q's are generators of a Lie algebra associated a SU(N) group. So Q's are traceless. Also we have
$$[P^a,P^b]=0$$
where P's are generators of a Lie algebra associated to an Abelian group. We have the following relation between these generators
$$[Q^a,P^b]=if^c_{ab}P^c$$

I would like to know what we can say above the following trace. Is it equal to zero?
$$tr([Q^a,P^b]Q^c P^d)$$

Comment:
From the cyclic property of trace we have
$$tr[A,B]=0$$
for any matrices. Also
$$tr([A,B]C)=0$$
just for symmetric matrices. Maybe these relations help!
Cheers!
 
Last edited:
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  • #2
Some quick calculations let me assume that this is not true. You could check the Poincaré algebra.
 

1. What is the purpose of calculating the trace of generators of two Lie algebra?

The trace of generators of two Lie algebra is used to study the relationship between two Lie algebras. It can help determine if the two algebras are isomorphic or not.

2. How do you calculate the trace of generators of two Lie algebra?

The trace of generators of two Lie algebra can be calculated by taking the sum of the diagonal elements of the commutator matrix, which is formed by taking the commutator of the generators of the two Lie algebras.

3. Can the trace of generators of two Lie algebra be negative?

No, the trace of generators of two Lie algebra is always a non-negative integer. This is because it represents the number of independent generators in the Lie algebra.

4. What does the trace of generators of two Lie algebra tell us about the structure of the Lie algebra?

The trace of generators of two Lie algebra provides information about the dimension and structure of the Lie algebra. It can also reveal if the Lie algebra is simple or not.

5. Are there any practical applications of calculating the trace of generators of two Lie algebra?

Yes, the trace of generators of two Lie algebra has applications in physics, particularly in the study of quantum mechanics and particle physics. It is also used in other areas such as differential geometry and representation theory.

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