Conformal mechanics 2026-10-06
A one-dimensional particle with admits conserved time-translation, dilation and special-conformal charges. Their Poisson brackets form the sl2R Lie algebra. The homogeneity of the inverse-square potential is what allows the symmetry.
Work away from , where the inverse-square potential is singular. Variation of the phase-space action gives
The last equation is the constraint imposed by the Lagrange multiplier . The canonical momentum conjugate to is , not . Consequently the nonzero canonical Poisson brackets are
In particular,
With the convention , the Noether charge generating is . Equivalently, the conserved physical energy is ; a convention that calls the energy the time-translation charge absorbs this minus sign into its parameter.
For the dilation charge,
on the constraint surface. Its infinitesimal canonical transformations are
For constant , extending this by preserves the action: the kinetic terms are invariant and scales oppositely to . Thus the dilation acts on time and position with their nonrelativistic relative scaling. Its Poisson bracket with the energy is
Put . Direct variation of the Hamiltonian gives
so
The supplied transformations are generated by the special conformal charge of inverse-square mechanics
Choose
Then even for a time-dependent parameter. Expanding the kinetic-term variation, keeping the terms in , gives
Hence
For a constant parameter only the boundary term remains, identifying as the Noether charge. Independently, the equations of motion give
Using the same canonical Poisson bracket convention,
Together, , and form the sl2R Lie algebra of conformal mechanics. These are time translation, dilation and special conformal transformation. A useful normalization check is the Casimir element
on the constraint surface.