- #1
deadringer
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We are asked to show that L(SO(4)) = L(SU(2)) (+) L(SU(2))
where L is the Lie algebra and (+) is the direct product.
We are given the hint to consider the antisymmetric 4 by 4 matrices where each row and column has a single 1/2 or -1/2 in it.
By doing this we generate four matrices, call them S1, S2, T1, T2
we can show that the commutator of S1, S2 generates another matrix S3 and that the same occurs for the T's. We can show that the 6 matrices form a general basis for L(SO(4))
we then get the following commutation relations:
[Sa, Sb] = epsilon(a,b,c) Sc
[Ta, Tb] = epsilon(a,b,c) Tc
and [Ta, Sb] = 0
We can then see that the S and T matrices form a basis for L(SU(2)) as they obey the correct commutation relations, and therefore the direct sum of these two Lie algebras forms the lie algebra for L(SO(4)).
My question is if we require the two L(SU(2))'s to commute (as they in this case do) in order use their direct sum, or is it okay to take a direct sum of two non-commuting lie algebras. thanks
where L is the Lie algebra and (+) is the direct product.
We are given the hint to consider the antisymmetric 4 by 4 matrices where each row and column has a single 1/2 or -1/2 in it.
By doing this we generate four matrices, call them S1, S2, T1, T2
we can show that the commutator of S1, S2 generates another matrix S3 and that the same occurs for the T's. We can show that the 6 matrices form a general basis for L(SO(4))
we then get the following commutation relations:
[Sa, Sb] = epsilon(a,b,c) Sc
[Ta, Tb] = epsilon(a,b,c) Tc
and [Ta, Sb] = 0
We can then see that the S and T matrices form a basis for L(SU(2)) as they obey the correct commutation relations, and therefore the direct sum of these two Lie algebras forms the lie algebra for L(SO(4)).
My question is if we require the two L(SU(2))'s to commute (as they in this case do) in order use their direct sum, or is it okay to take a direct sum of two non-commuting lie algebras. thanks