# nLab higher symplectic geometry

### Context

#### Symplectic geometry

symplectic geometry

higher symplectic geometry

# Contents

## Idea

Higher symplectic geometry is the generalization of symplectic geometry to the context of higher geometry.

It involves two kinds of generalizations:

1. the symplectic form generalizes from a 2-form to a form of arbitrary arity. This aspect is called multisymplectic geometry.

2. the base manifold is generalized to a smooth ∞-groupoid or ∞-Lie algebroid. For binary symplectic forms this is called a symplectic Lie n-algebroid.

In the full higher symplectic geometry both of these aspects are unified: a multisymplectic $\infty$-groupoid is a smooth ∞-groupoid equipped with a differential n-form on smooth ∞-groupoids satisfying some condition.

Examples of higher symplectic geometries arise naturally as the covariant phase spaces “over the point” or “in top codimension” (in the sense of extended topological quantum field theory) in systems of ∞-Chern-Simons theory: their $\infty$-multisymplectic form is the invariant polynomial that defines the theory.

## Definition

###### Definition

Let $\mathfrak{a}$ be an L-∞ algebroid. For $n \in \mathbb{N}$, an n-plectic form or multisymplectic form of $n$ arguments on $\mathfrak{a}$ is

• an invariant polynomial $\omega$ on $\mathfrak{a}$ which is $n$-linear (takes $n$ arguments):

$\omega \in W^n(\mathfrak{a}) = \Omega^n(\mathfrak{a}) \,;$
• such that the contraction morphism

$\iota_{(-)}\omega : T \mathfrak{a} \to W^{n-1}(\mathfrak{a}) = \Omega^{n-1}(\mathfrak{a})$

in injective.

###### Example

If $\mathfrak{a}$ is a Lie 0-algebroid (over a smooth manifold) then it is simply that smooth manifold, $\mathfrak{a} = X$. In this case $W(\mathfrak{a}) = \Omega^{\bullet}(X)$ is the ordinary de Rham complex and an invariant polynomial is a closed differential form of positive degree.

In this case an $n$-plectic form on $\mathfrak{a}$ is a closed $n$-form $\omega(-,-,.\dots, -)$ on $X$ such that for every vector field $v \in \Gamma(T X)$ we have

$(\omega(v,-,\cdots,-) = 0) \;\; \Rightarrow \;\; (v = 0).$

## Applications

### Higher Chern-Simons theory

Every invariant polynomial $\omega$ induces an ∞-Chern-Simons theory action functional

$S_{CS} : \Omega(\Sigma,\mathfrak{a}) \to \mathbb{R} \,.$

The variation of that functional is

$\delta S_{CS} : A \mapsto \int_\Sigma \omega(\delta A, F_A, \cdots, F_A) \,.$

Therefore the condition that the invariant polynomial is $n$-plectic amounts to saying that $S_{CS}$ has no spurious global symmetries.

(…)

duality between algebra and geometry in physics:

∞-Chern-Simons theory from binary and non-degenerate invariant polynomial

$n \in \mathbb{N}$symplectic Lie n-algebroidLie integrated smooth ∞-groupoid = moduli ∞-stack of fields of $(n+1)$-d sigma-modelhigher symplectic geometry$(n+1)$d sigma-modeldg-Lagrangian submanifold/ real polarization leaf= brane(n+1)-module of quantum states in codimension $(n+1)$discussed in:
0symplectic manifoldsymplectic manifoldsymplectic geometryLagrangian submanifoldordinary space of states (in geometric quantization)geometric quantization
1Poisson Lie algebroidsymplectic groupoid2-plectic geometryPoisson sigma-modelcoisotropic submanifold (of underlying Poisson manifold)brane of Poisson sigma-model2-module = category of modules over strict deformation quantiized algebra of observablesextended geometric quantization of 2d Chern-Simons theory
2Courant Lie 2-algebroidsymplectic 2-groupoid3-plectic geometryCourant sigma-modelDirac structureD-brane in type II geometry
$n$symplectic Lie n-algebroidsymplectic n-groupoid(n+1)-plectic geometry$d = n+1$ AKSZ sigma-model