Symmetries and conserved quantities

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Discussion Overview

The discussion revolves around the conservation of angular momentum in different types of symmetric potentials, specifically comparing spherically symmetric and elliptically symmetric potentials. Participants explore the implications of these symmetries on the conservation laws applicable to particles within these potentials.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant asserts that angular momentum is conserved in a spherically symmetric potential and questions whether a similar conservation applies in an elliptically symmetric potential.
  • Another participant suggests that angular momentum conservation arises from the rotational invariance of the Hamiltonian, implying it should hold in some form for elliptical potentials.
  • A different viewpoint argues that angular momentum, defined as \(\vec x \times \vec p\), does not have a comparable conserved quantity in a generic elliptically symmetric potential.
  • One participant proposes that if the elliptically symmetric potential is specifically defined, angular momentum along a certain axis (z-axis) could be conserved.
  • Another participant mentions that in the context of an elliptic potential well, the total angular momentum is not a good quantum number due to mixing of energy eigenvalues.
  • A later reply clarifies that while angular momentum around the azimuthal direction may be conserved, the total angular momentum is not conserved in the case of an elliptical potential.

Areas of Agreement / Disagreement

Participants express differing views on the conservation of angular momentum in elliptical potentials, with no clear consensus reached on the conditions under which conservation may or may not hold.

Contextual Notes

Participants reference specific forms of potentials and quantum mechanical implications, indicating that the discussion may depend on the definitions and assumptions regarding the symmetry of the potentials involved.

plmokn2
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I know that if a particle is in a spherically symetric potential its angular momentum will be conserved, but what about if somehow we manage to produce say an elliptically symmetric potential? Will the particle then have a momentum along the curve of the ellipse conserved?
Thanks
 
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It should be, because the conservation of angular momentum is from the
rotational invariance of the Hamiltonian.
 
No. Angular momentum is not "momentum along the curve of a circle", but rather [itex]\vec x\times\vec p[/itex]. There is nothing comparable that is conserved for a generic elliptically symmetric potential.
 
I think his 'momentum' here is angular momentum.
If your elliptically symmetric potential is [tex]V(\rho,z)=\frac{1}{\rho^2+\alpha z^2},~\alpha\neq 1[/tex], then angular momentum along axis
'z' is conserved.
 
Last edited:
The only thing i can remember know is that in case of an elliptic potential well, J = L + S is not a good quantum number, science the energy eigenvalues will be "mixed" with same M_J etc, c.f The Nilsson model of Atomic Nucleus.
 
Thanks for your replies, sorry for the slightly ambiguious question.
 
Angular momentum around the azimuthal direction will still be conserved, but the TOTAL angular momentum will not. This is basically what PRB147 said, but maybe slightly clarified.
 

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