- #1
francesco75
- 3
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We know that the Newton binomial formula is valid for numbers
in elementary algebra.
Is there an equivalent formula for commuting spherical tensors? If so,
how is it?
To be specific let us suppose that A and B are two spherical tensors
of rank 1 and I want to calculate (A + B)4 and I want
the result to be a scalar. The two tensors commute, AB=BA.
If I apply naively the binomial formula I have the usual expansion,
with one of term being
[tex]
\frac{4!}{2! (4-2)!} A^2 B^2
[/tex],
where the superscript denotes the number of tensors, i.e. the order.
But according to the rules of the tensors coupling algebra, there are different
ways to couple 4 tensors of rank 1 to a scalar. So my wild guess is that the above
terms should be
[tex]
(\frac{4!}{2! (4-2)!} )(\left[ A^2_0 B^2_0\right]_0+
\left[ A^2_1 B^2_1 \right]_0+
\left[ A^2_2 B^2_2 \right]_0)
[/tex],
where the subscripts are the total rank of the couplings, which are 0,1 and 2 for two tensors of rank 1 coupled togheter.
The other terms should go the same way, that is one is putting all the possible
coupling to the scalar according to the orders of the tensors.
Am I correct?
Tank you very much
in elementary algebra.
Is there an equivalent formula for commuting spherical tensors? If so,
how is it?
To be specific let us suppose that A and B are two spherical tensors
of rank 1 and I want to calculate (A + B)4 and I want
the result to be a scalar. The two tensors commute, AB=BA.
If I apply naively the binomial formula I have the usual expansion,
with one of term being
[tex]
\frac{4!}{2! (4-2)!} A^2 B^2
[/tex],
where the superscript denotes the number of tensors, i.e. the order.
But according to the rules of the tensors coupling algebra, there are different
ways to couple 4 tensors of rank 1 to a scalar. So my wild guess is that the above
terms should be
[tex]
(\frac{4!}{2! (4-2)!} )(\left[ A^2_0 B^2_0\right]_0+
\left[ A^2_1 B^2_1 \right]_0+
\left[ A^2_2 B^2_2 \right]_0)
[/tex],
where the subscripts are the total rank of the couplings, which are 0,1 and 2 for two tensors of rank 1 coupled togheter.
The other terms should go the same way, that is one is putting all the possible
coupling to the scalar according to the orders of the tensors.
Am I correct?
Tank you very much
Last edited: