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Orbital angular momentum eigenstates of the massive model: spherical harmonics, the l,m quantum numbers and the Casimir value
A conditional consequence of P1, P2, P5 and P6 for the massive spin-s model and its orbital generators: for a smooth compactly supported radial profile times a spherical harmonic, the model vector is an eigenvector of the third orbital generator with eigenvalue hbar m, the Casimir quadratic form takes the value hbar^2 l(l+1), and the orbital quantum numbers are those of the spherical harmonic family. The statement concerns the spatial factor only, uses no dynamics and no measurement model, and asserts no spectral decomposition of the full spatial Hilbert space, no hydrogen spectrum and no empirical result.
Statement
Adopt the state and composition postulate P1, the observable and probability postulate P2, the kinematics and massive-particle model postulate P5 and the internal-factor assignment of the spin postulate P6, read for the massive spin- model of The massive spin-s particle model of the framework: state space, operators, units and frame readings and the angular momentum readings of Orbital, spin and total angular momentum of the massive spin-s model: assigned sharp observables, units and readings (State and composition postulate P1: Hilbert spaces, preparations and composite systems, Observable and probability postulate P2: self-adjoint observables, spectral probability and finite unsharp outcomes, Kinematics and massive-particle model postulate P5: Newtonian frames and one-particle operators, Identical-particle and spin assignments P6: permutation sectors and finite-spin representations), and assume the Axiom of Choice and the Axiom of Countable Choice (The Axiom of Choice, The Axiom of Countable Choice ()). Fix , , a unit vector and a complex-valued , and let be the harmonic homogeneous polynomial of degree with of Harmonic polynomial dimension clause (c) (Associated Legendre function normalization). Define the model vector Then:
(a) is a well-defined class in the model's state space and in fact ; it lies in for each , and for so that is the polynomial representative of the sphere function of Orbital self-adjoint generators; in particular ;
(b) with one has and so the Casimir quadratic form of the model's orbital generators on takes the value ;
(c) consequently, for the pure preparation of the unit vector (for ), the mean and the second moment of the outcome law of are finite and equal and , so the variance vanishes; for each the mean and second moment of the law of are finite and the second moment equals ; the model reads as the orbital angular momentum quantum numbers of the preparation, in the sense of the eigenvalue of the angular momentum-squared form and the eigenvalue of ;
(d) Scope. Clauses (a)-(c) are conditional consequences of P1, P2, P5, P6 and the cited mathematics, and concern the spatial factor of the massive model. The item asserts no dynamics, no measurement or apparatus model, no joint sharp values of two different components , no empirical value and no spectral resolution of : the identity is a quadratic-form statement on the displayed smooth vectors and is not read as a statement about a self-adjoint operator on the full spatial Hilbert space.
Facts & Assumptions
Given: The postulates P1, P2, P5 and P6 in the stated readings; the Axiom of Choice and the Axiom of Countable Choice; the model with parameters , , ; the harmonic polynomial and the sphere functions ; the radial function ; the unit vector ; the vector ; indices .
Harmonic polynomial and spherical harmonic. For and the polynomial is homogeneous of degree , harmonic, nonzero, with , and where ; moreover and for (Harmonic polynomial dimension clause (c), Orbital self-adjoint generators clauses (a),(c), Associated Legendre function normalization clause (c)).
Core action of the orbital generators. For every componentwise Schwartz class the orbital generators satisfy , , and with the componentwise weak derivative (Coordinate-rotation generators on the Schwartz classes and their commutators clauses (a),(b), Componentwise position and momentum operators on the component-valued wave-function space clauses (a),(c)).
Orbital Casimir identity. For one has on the harmonic span, and the on-shell values are exactly the squared norms (The orbital Casimir identity: the restrictions of the orbital generators to the degree-l blocks are spin-l models clauses (b),(c), Orbital self-adjoint generators).
Polar integration and the sphere measure. For a Borel on one has , and with (Polar coordinates decompose Lebesgue measure into r^{n-1} dr d sigma, Sphere integrals in angle coordinates).
Schwartz calculus and the class reading. ; a classical partial derivative of a function that is locally integrable is its weak derivative; the model space consists of almost-everywhere classes (Schwartz space and its seminorms, Componentwise position and momentum operators on the component-valued wave-function space, The space as the quotient by null functions, Complex Lp classes and Euclidean test-function conventions, Hilbert space, Real and complex inner product spaces, with the inner product linear in the first argument).
Proof
Proof technique: direct; the vector is a compactly supported smooth class with a homogeneous polynomial angular factor, so the core identity of the generators applies; the radial and angular integrals separate by polar integration and the Casimir value is transported from the sphere.
Given: The data of the statement and [F1]-[F5].
[Smoothness and the polynomial identity] Since with and is a polynomial, the function vanishes identically near and is smooth on with compact support, so by [F5]; for and each , the product rule gives because , and by [F1] the function is the polynomial representative of ; moreover [F1] gives .
[Core action and eigenvalue] By step 1.1 and [F2], and for almost every , where the weak derivatives agree with the classical ones by [F5]; here on the Schwartz class, so the factor occurs once. For , [F1] gives , proving (a).
[Norms and the Casimir form] Put . Each term is homogeneous of degree or zero, so for ; for , . By step 2.1, and polar integration [F4], . By [F1], , hence . Likewise homogeneity of and [F4] give , using the normalization in Associated Legendre function normalization clause (d). Finally, on the finite invariant block , self-adjointness and [F3] give , so , proving (b), including and .
[Readings] Let and put ; by step 2.1, with , so the mean and the second moment of the law of in the pure preparation are and , with variance ; for each , step 2.1 gives and step 3.1 gives , so the mean and second moment of the law of are finite with that second moment, and the quadratic form is , which is (c).
[Assembly and scope] Steps 1.1 and 2.1 prove (a), step 3.1 proves (b) and step 4.1 proves (c); only the spatial core identities, the sphere data and polar integration were used, no dynamics, apparatus or empirical input entered, and no operator identity for on the full space was asserted, which is the scope statement (d).
Remarks
- The density of the family. The vectors with span a dense subspace of the angular sector in the polar decomposition; this theorem uses only their eigenproperty and makes no completeness claim.
- No hidden operator . The Casimir value is stated as a quadratic-form identity. Defining a self-adjoint operator on would require a separate closed-form and domain argument, which is not part of this page.
Depends on
The Axiom of Choice
Complex Lp classes and Euclidean test-function conventions
The Axiom of Countable Choice ()
Hilbert space
Real and complex inner product spaces, with the inner product linear in the first argument
The space as the quotient by null functions
Orbital, spin and total angular momentum of the massive spin-s model: assigned sharp observables, units and readings
Dimensions, SI unit conventions and quantity types of the framework
The massive spin-s particle model of the framework: state space, operators, units and frame readings
Assigned sharp observables and the outcome law of the framework
The state space of the framework: preparations, pure rays and density operators
Schwartz space and its seminorms
The orbital Casimir identity: the restrictions of the orbital generators to the degree-l blocks are spin-l models
Componentwise position and momentum operators on the component-valued wave-function space
Sphere integrals in angle coordinates
Coordinate-rotation generators on the Schwartz classes and their commutators
Identical-particle and spin assignments P6: permutation sectors and finite-spin representations
Kinematics and massive-particle model postulate P5: Newtonian frames and one-particle operators
Observable and probability postulate P2: self-adjoint observables, spectral probability and finite unsharp outcomes
State and composition postulate P1: Hilbert spaces, preparations and composite systems
Associated Legendre function normalization
Harmonic polynomial dimension
Orbital self-adjoint generators
Sphere Laplacian diagonal domain
Sphere ONB
Polar coordinates decompose Lebesgue measure into r^{n-1} dr d sigma
Dependency tree · 2 levels
Sources
- J. Binney and D. Skinner, The Physics of Quantum Mechanics, Section 7.2, printed pages 145-154 (PDF pages 153-162): spherical harmonics as angular momentum eigenfunctions with quantum numbers l and m and the eigenvalue l(l+1) of the Casimir
- D. Tong, Quantum Mechanics (author-hosted lecture set), Sections 4.1-4.1.2, printed pages 96-103 (PDF pages 99-106): orbital angular momentum, the commutators, the l,m quantum numbers and the l = 0 exceptions
- B. Zwiebach, MIT 8.05 Quantum Physics II (Fall 2013), Chapter 9 'Angular Momentum', Section 1, printed pages 1-11: orbital angular momentum and the spherical harmonic eigenvalues in the radial problem