Past exam of the mathematics course of the University of Cambridge 2016 iii Paper 306 1 i Solution Created 2026-10-03 Updated 2026-10-06
Work away from , where the inverse-square potential is singular. Variation of the phase-space action givesThe last equation is the constraint imposed by the Lagrange multiplier . The canonical momentum conjugate to is , not . Consequently the nonzero canonical Poisson brackets areIn 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 areFor 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 givessoThe supplied transformations are generated by the special conformal charge of inverse-square mechanicsChooseThen even for a time-dependent parameter. Expanding the kinetic-term variation, keeping the terms in , givesHenceFor a constant parameter only the boundary term remains, identifying as the Noether charge. Independently, the equations of motion giveUsing 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 elementon the constraint surface.
sl2R Lie algebra 2026-10-06
The real traceless two-by-two matrices form a three-dimensional Lie algebra. A basis adapted to conformal mechanics obeys , , .