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Ch 4 Dirac Sections
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Word file of draft equation sections for Ch 4, dated 2015 and marked in 2016 as reviewed and can be discarded. It gives Dirac bra-ket formulas for tensor products, the wedge product of kets (Sec 4.3) and of bras (Sec 4.4), antisymmetry, components, determinant expansions, and the equivalence of the spaces Λ2 and Λ2f of antisymmetric bilinear functions.
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This is the Title PhL 1.11.15
Reviewed on 5.16.16, can discard, Dirac sections for Ch 4
Note that page numbering is turned on in this template and view is 125%,
located in phil/roaming/microsoft/templates size about 219K.
ei = |ei> e'i = |e'i> bases for V and W
eie'j = |ei> |e' > basis for the tensor product space VW
vw = |v> |w> a pure "vector" in the tensor product space VW (4.1.1a)
T = |T> = Σij Tij |ei> |e'j> rank-2 tensor in VW
(a b)ij = <ei| <ej| |a> |b> = <ei|a> <ej|b> = aibj outer product
a b = <a | b> dot product
|v> |w> = Σijviwj |ei> |e'j> expansion of pure vector on basis vectors (4.1.6a)
T ≡ |T> = Σij Tij |ei> |e'j> expansion of a rank-2 tensor (4.1.7a)
<a| <b| |c> |d> = <a|c><b|d> = Σiaici Σjbjdj = Σijaibjcidj dot product in V2 (4.1.12a)
**********************
Section 4.3 (a)
|a> ^ |b> = ( |a> |b> - |b> |a> )/2 (4.3.1a)
|a> ^ |b> = - |b> ^ |a> (4.3.2a)
|a> ^ |a> = 0 (4.3.3a)
T^ = |T^> = Σij Tij |ei> ^ |ej> (4.3.5a)
T^ab = < ea| <eb | |T^> = < ea| <eb | Σij Tij |ei> ^ |ej>
= Σij Tij <ea| <eb | [ |ei> |ej> - |ej> |ei> ]/2
= Σij Tij [ <ea |ei> <eb |ej> - <ea |ej> <eb |ei> ]/2
= Σij Tij [ δaiδbj- δajδbi]/2 = (Tab - Tba)/2 = - T^ba (4.3.7a)
Section 4.3 (b)
T^ = |T^> = Σi<j Aij |ei> ^ |ej> (4.3.10a)
Section 4.3 (c)
|a> ^ |b> = Σij aibj |ei> ^ |ej> = Σi<j det |ei> ^ |ej> (4.3.12a)
|a> ^ |b> ^ |c> = det(a,b,c) |e1> ^ |e2>^ |e3> n = 3 (4.3.15a)
Section 4.3 (d)
(a ^ b)rs = <er| <es | |a> ^ |b> = <er| <es | ( |a> |b> - |b> |a> )/2
= [ <er| <es | |a> |b> - <er| <es | |b> |a> ]/2
= [ <er |a><es |b> - <er |b><es |a> ]/2 = (arbs - asbr)/2 (4.3.27a)
Section 4.3 (e)
(ei^ej) (cd) = [(eic)(ejd) - (ejc)(eid)]/2 = [cidj - cjdi]/2 .
<ei| ^ <ej| |c> |d> = (1/2)[<ei| <ej| - <ej| <ei| ] |c> |d>
= (1/2)[ <ei| c><ej|d> - <ej| c><ei|d> ] = (1/2) [ cidj - cjdi] (4.3.33a)
****************
Section 4.4 (a)
<α| ^ <β| = (<α| <β| - <α| ^ <β| )/2 (4.4.1)D
<α| ^ <β| = - <β| ^ <α| (4.4.2)D
<α| ^ <α| = 0 (4.4.3)D
T^ = <T^| = Σij Tij <ei| ^ <ej| // λi = <ei| (4.4.5)D
T^ = <T^| = Σijαiβj <ei| ^ <ej| = ( Σiαi<ei| )( Σjβi<ej| ) = <α| ^ <β| (4.4.6)D
Section 4.4 (b)
T^ = <T^| = Σi<j Aij <ei| ^ <ej| (4.4.10)D
Section 4.4 (c)
α ^ β = <α| ^ <β| = Σi<j det <ei| ^ <ej| (4.4.12)D
Section 4.4 (d)
(λi^ λj)(vr,vs) = <ei| ^ <ej| | vr> | vs> = (1/2) (<ei| <ej| - <ej| <ei| ) | vr> | vs>
= (1/2) ( <ei|vr><ej| vs> - <ei|vs><ej| vr>) = (1/2) [ (vr)i(vs)j - (vr)j(vs)i] (4.4.20b)D
The vector spaces Λ2 and Λ2f
Looking at (4.4.20), (4.4.23) and (4.4.29), one sees that (λi^ λj)(vr,vs), (α ^ β)(vr,vs) and T^(vr,vs) are all antisymmetric bilinear functions of the two arguments vr, vs ϵ V .
In Section 4.3 we declare that the rank-2 tensor T^ = |T^> is antisymmetric (alternating) if T^ab = - T^ba . In similar fashion, we declare that the rank-2 tensor functional T^ = <T^| is antisymmetric (alternating) if T^(v,v') = - T^(v',v). That is to say, saying that the functional is alternating means that the corresponding tensor function is alternating. Section A.10 writes <T^| = <Alt T | in an attempt to declare the asymmetry of <T^| without reference to the corresponding tensor function, "it is just notation".
We can regard both T^ = <T^| and T^(v,v') = <T^|v,v'> as representations of the same antisymmetric rank-2 tensor functional <T^| in V* ^ V* = Λ2. The object T^ is an asymmetric bilinear rank-2 tensor functional, whereas T^(v,v') is an asymmetric bilinear rank-2 tensor function (a Spivak 2-tensor). There is a 1-to-1 correspondence between T^ and T^(v,v') . We shall say T^ ϵ Λ2 while T^(v,v') ϵ Λ2f (f = function), and the two spaces are isomorphic.
Fact: The vector space Λ2 is equivalent to the vector space Λ2f of asymmetric bilinear functions on V2. (4.4.34)
This may be compared to our earlier statement for the larger space V*2 = V*V* ,
Fact: The vector space V*2 is equivalent to the vector space V*2f of bilinear functions on V2. (4.2.15)