This is a sub-entry of ∞-Chern-Simons theory. See there for background and context.
The covariant phase space
We describe the covariant phase spaces of ∞-Chern-Simons theory:
the space of solutions to its Euler-Lagrange equations of motion,
the canonical presymplectic structure on that space
and – eventually – its reduction to a genuine symplectic structure after homotopically dividing out gauge transformations: after passage to a Lagrangian submanifold of the derived critical locus.
By the discussion at ∞-Chern-Simons theory -- action functionals we have that the action functional is itself a representative of a characteristic class, in degree 0, in the cohesive (∞,1)-topos Smooth∞Grpd. Accordingly, it has itself a differential refinement:
We call the configuration space of the -Chern-Simons theory over .
The postcomposition of the smooth action functional with the universal curvature characteristic form
we call the Euler-Lagrange equations of -Chern-Simons theory over .
The critical locus the action functional, hence the homotopy fiber of regarded as a section of the cotangent bundle, hence the (∞,1)-pullback
we call the covariant phase space of -Chern-Simons theory over .
Equations of motion and presymplectic covariant phase space
Given any local action functional, its Euler-Lagrange equations determine the corresponding covariant phase space canonically equipped with a presymplectic structure.
We determine the presymplectic covaraint phase space of the explicit action functional presentation discussed here.
Let be an L-∞ algebra with -ary invariant polynomial . Then the ∞-connections with values in that satisfy the equations of motion of the corresponding -Chern-Simons theory are precisely those for which
where denotes the (in general inhomogeneous) curvature form of .
Let be a 1-parameter variation of , that vanishes on the boundary . Here we write for the canonical coordinate on the interval.
Notice that the curvature is
For the given path of fields we may write
By definition is critical if
for all extensions of . Using Cartan's magic formula and the Stokes theorem the left hand expression is
where we used that by assumption and hence vanishes on . This yields the equations of motion as claimed.
The canonical presymplectic potential on the space of solutions is
where is inserted, termwise, for a curvature form.
Comparing in the proof of prop. 1 the structure of the boundary term with the formula for the presymplectic structure discussed at covariant phase space we see that the presymplectic potential is
Here we are using that and . Therefore the cocycle summand in the Chern-Simons element drops out.
For a binary and non-degenerated invariant polynomial (as for ordinary Chern-Simons theory) the equations of motion are
and the presymplectic structure on the space of solutions is
We discuss the gauge symmetry of the -Chern-Simons action functionals.
Gauge transformations of -algebroid valued forms
The genuine gauge transformations of L-∞-algebroid valued differential forms? are symmetries of the -Chern-Simons action functional, by the invariance property of invariant polynomials.
Global gauge transformations
Suppose there exists such that
Then by the above the “constant” transformation
is a symmetry of the the -Chern-Simons action.
These spurious global symmetries are absent precisely if is n-plectic, hence if constitutes a higher symplectic geometry.
The ∞-Chern-Simons theory action functional is manifestly invariant under diffeomorphisms . But only in special cases does this invariance not add to the ghost-structure of the BV-BRST complex on top of the gauge ghosts contained already in :
If the invariant polynomial that defines the -Chern-Simons theory is binary and non-degenerate, then on covariant phase space every diffeomorphism connected to the identity is related by a gauge transformation to the identity:
The assumption that the invariant polynomial is binary and invariant implies with corollary 1 that the equations of motion are .
Let be the vector field generating the diffeomorphism. Then for a field configuration its iamge under the gauge transformation is , where is the Lie derivative along . By Cartan's magic formula and the equations of motion we have
is the gauge parameter and is the covariant derivative
derived at connection on a principal infinity-bundle in the subsection infinitesimal gauge transformations. As discussed there, this are the infinitesimal gauge transformations in .
See also the references at ∞-Chern-Simons theory.
A discussion of Chern-Simons theory for higher degree invariant polynomials (but on ordinary Lie algebras) is for instance in
- Maximo Banados, Luis Garay, Marc Henneaux, Existence of local degrees of freedom for higher dimensional pure Chern-Simons theories Phys. Rev. D. vol 53, nr 2 (1996)