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Slater direct and exchange calculation
Statement
Slot convention. For , acts on as in Permutation sector projections on the n-fold tensor power. On one-based tuple positions use for . Conjugation by gives and ; thus the supplier's tensor action becomes . The parameters of and remain canonical zero-based permutations.
Assume the Axiom of Countable Choice and the Axiom of Choice (The Axiom of Countable Choice (), The Axiom of Choice). Let be a complex Hilbert space with completed tensor powers and symmetric projections (Hilbert tensor construction: inner product, completion and product bases, Permutation sector projections on the n-fold tensor power). Then:
(a) Slater vectors: for and orthonormal , the Slater vector satisfies and ;
(b) exclusion: if for some , then (Permutation sector projections on the n-fold tensor power (d));
(c) two orbitals, bounded pair interaction: let be normalized and orthogonal, let be measurable and bounded with for a.e. , let be the Euclidean product unitary (Euclidean L² product unitary: L²(R^a)⊗̂L²(R^b) ≅ L²(R^{a+b})), put and integrals of absolutely integrable functions. Then and the pair expectation of the multiplier in the two spatial states is
(d) repulsive Coulomb exchange: let , , let be normalized and orthogonal (Integer-order Sobolev spaces and their norms, The space as the quotient by null functions). The vectors belong to : Hardy translated in the variable and Tonelli give , and the swapped product has the same property. Then the integrals and converge absolutely, , with ; consequently , i.e. the antisymmetric spatial pair state has the lower expectation of the repulsive Coulomb pair interaction.
The exchange calculation is a statement about the indicated spatial vectors; it does not deduce the spin-statistics assignment of any species, and combining the spatial states with spin requires a separately stipulated symmetry rule. No physical interpretation of , or the states is asserted.
Facts & Assumptions
Given: orthonormal vectors , normalized orthogonal , a bounded measurable even , the pair multiplier on , the numbers , and .
The permutation unitaries satisfy , , and whenever two of the coincide; elementary tensors have norm (Permutation sector projections on the n-fold tensor power, Hilbert tensor construction: inner product, completion and product bases).
Cauchy-Schwarz and the product structure: for , , and for bounded measurable , (Cauchy-Schwarz inequality for , The space as the quotient by null functions, Complex Lp classes and Euclidean test-function conventions).
Hardy for : (Three-dimensional Hardy bound (c)).
Gaussian integrals and transforms: ; for the Euclidean Fourier transform of is ; the identity for follows by the substitution (The Gaussian integral , Euclidean Gaussian transform with the 2π normalization, Plancherel theorem).
Tonelli for -finite product spaces permits the interchange of the order of integration for nonnegative measurable integrands (Tonelli's theorem for nonnegative measurable functions on a sigma-finite product).
The Euclidean product unitary satisfies ; because acts on , the spatial pairing is , in the inner product linear in the first argument (Euclidean L² product unitary: L²(R^a)⊗̂L²(R^b) ≅ L²(R^{a+b})). Once Tonelli establishes absolute integrability, Fubini applies separately to real and imaginary parts (Fubini's theorem for L^1 functions on a sigma-finite product).
Proof
[Slater norm and identity] For , the tensor inner product is by [F1], which equals if and otherwise because the are orthonormal. Hence the summands of are mutually orthogonal of norm , so and . Moreover , using and reindexing . This proves (a).
[Exclusion] The assertion (b) is exactly [F1]'s vanishing statement for on a tensor with two equal factors; in particular for , .
[Two-orbital expansion] Assume the hypotheses of (c). Absolute integrability of the four products , follows from [F2]: e.g. and . Expanding the four terms in the tensor representation of [F6] gives , where ; replacing by and using gives , so the expectation is . Since is real and even, exchanging the two integration variables in shows , so and ; the same symmetry with real gives . This proves (c).
[Absolute convergence for the Coulomb kernel] Assume the hypotheses of (d). For the direct term, by [F3] applied in the -variable for a.e. and Cauchy-Schwarz, , so with Tonelli [F5] . For the crossed term use and the same bound to conclude . Hence are absolutely convergent and .
[Gaussian positivity with only data] Put by [F2], with no assumption that . Step 1.4 gives . The Gaussian representation [F4], Tonelli on absolute values [F5] and complex Fubini [F6] therefore give , where . For completion of the square and the three-dimensional Gaussian integral give . The triple integral of its absolute integrand is , finite by Tonelli. Complex Fubini then yields . The outer integral is absolutely convergent by the first bound from step 1.4 and the Gaussian kernel identity, so and is real. Since , the two absolutely convergent interaction expectations satisfy under the full original hypotheses.
[Conclusion and scope] Steps 1.1 and 1.2 prove (a) and (b), steps 1.3 and 1.4 prove (c), and step 2.1 proves (d). The final paragraph of the statement records that the spin-statistics assignment and any physical interpretation are separate assumptions: the symmetric () and antisymmetric () spatial vectors are mathematical vectors, and combining them with spin requires a stipulated symmetry rule. This completes the proof.
Depends on
Fubini's theorem for L^1 functions on a sigma-finite product
Fixed-N Coulomb self-adjointness
Hilbert tensor construction: inner product, completion and product bases
Permutation sector projections on the n-fold tensor power
Euclidean L² product unitary: L²(R^a)⊗̂L²(R^b) ≅ L²(R^{a+b})
Three-dimensional Hardy bound
Cauchy-Schwarz inequality for
Plancherel theorem
Euclidean Gaussian transform with the 2π normalization
The Gaussian integral
Tonelli's theorem for nonnegative measurable functions on a sigma-finite product
Integer-order Sobolev spaces and their norms
The space as the quotient by null functions
Complex Lp classes and Euclidean test-function conventions
Hilbert space
The Axiom of Countable Choice ()
The Axiom of Choice
Dependency tree · 2 levels
Sources
- F. H. L. Essler, Advanced Quantum Theory (Oxford lecture notes, 2017/18), Section 1.4.3 pp. 11-13 (two-particle operators, direct and exchange terms)
- R. Fitzpatrick, Quantum Mechanics (University of Texas at Austin, author-hosted course text), Chapter 6 Sections 6.4-6.5 pp. 88-93 (two-particle systems and identical particles)