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Appendix D rewrite
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Phil's dated working notes (2/25/12) on rewriting Appendix D of his curvilinear tensor document. He asks how the appendix changes if tensor densities are defined with J rather than |J|, as in Weinberg, and how parity should be handled. He logs the failure of the Weight Changing Theorem, the role of the sign factor σ in the oriented N-piped face area, and the C = curl B result, now a vector of weight -1. He concludes the new appendix was installed.
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The use of abs value |J| in tensor density PhL 2.25.12
This is a full Appendix D rewrite!
Opening comments:
Weinberg does not use the absolute value in his book.
I have run into a "σ problem" when I use absolute values
all weights I have seen so far are integers.
the only place I ever make use of tensor densities is my Section 8 which is now under rewrite!
So what would my Appendix D look like if I dispensed with the absolute value in the definition of a tensor density? Let's copy and paste it right here, then edit and see what happens. This is a very LONG 22 page appendix, so this will take a while to do. I will convert each section to blue after it is processed.
Log of editing.
(1) First trouble point is that my Weight Changing Theorem fails. Where do I use this theorem? One place is in section (h) where I am trying to show that C = curl B transforms as a regular vector. Maybe this conclusion is wrong if parity is included! Basically I am now trying to correctly incorporate parity into this appendix. I use the weight changing theorem 3 more times toward the end of App D.
So, when parity is included, is the definition of a tensor density as in Weinberg and me correct?
T' abcde = J-W Raa' Rbb' Rcc' Rdd' Ree' Ta'b'c'd'e'
Or should there be a factor σW present, in which case I am back to the old appendix D!
Digression: I am suddenly suspicious of the σ factor which I put in this equation
(An)i = σ (-1)n-1 εiabc..x (e1)a(e2)b.... (eN)x // en missing
For example, if N = 3 we would have
A3 = σ e1 x e2 σ = sign of det(S)
Why should the direction of this N-piped face area be a function of S which after all is the transformation from x space to x'-space, whereas here I am just doing everything in x-space which does not know about S. Ok, we have to now push down another level on "the stack". Go resolve that in a different doc, then when that is stabilized, return here and continue.
Resolution: (see "should sigma be in the dA form.. ") Yes, x-space stays the same, but under parity the N-piped spanned by the en inverts itself, so that all outfacing faces have a change in vector direction. The front of a cube becomes the back. If we want the vector definition to be outfacing, the sign has to change. Since the sign of e1 x e2 does not change when each of these en changes sign, the σ brings in that required sign change. I am happy again.
Comment: I used to have the full edited Appendix D sitting right here, all converted to blue as I edited it and fixed things up.
The main edit was getting rid of the Weight Changing theorem which, though valid, was not necessary since it is just a special case of the usual weight addition rule.
Another major change was to repair the C = curl B result, and I showed that this is a vector of weight -1, a change in my thinking on this subject. I repaired the curl derivation Section 12 and all went well there.
Another major change was going from |J| to J in all the tensor density stuff!
I did a full spelling check right here before my cut and paste. All done, we have a brand new Appendix D installed.