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6 votes
1 answer
473 views

Non-Hamiltonian actions in physics

I was reading the following article when I came across the interesting sentence "non-Hamiltonian [symplectic group] actions also occur in physics" I took a cursory look at the article cited but not …
2 votes
0 answers
99 views

Effective actions by non-commutative groups have non-commuting fundamental vector fields?

I have a bit of a contradiction in my brain and I was hoping once again that excellent Mathoverflow community could help me out :) Let $\rho_g$ be the action associated to a non-abelian Lie Group $G$ …
2 votes
0 answers
480 views

How to make sense of the Euler Lagrange equations for an infinite action?

The Euler–Lagrange equation is an equation satisfied by a function $q$, which is a stationary point of the functional $S(\boldsymbol q) = \int_a^b L(t,q(t),\dot{q}(t))\, \mathrm{d}t$ Say we have an …
4 votes
1 answer
230 views

Contradiction between fixed points of a hamiltonian diffeomorphism of a torus and quasi-peri...

Again a very simple question. I currently hold two contradictory ideas in my head 1) A hamiltonian diffeomorphism of a torus necessarily has fixed points 2) most hamiltonian actions on a torus in an …