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Hamiltonian systems, symplectic flows, classical integrable systems

1 vote

Characterization of bi-Hermitian structures with equal Lee forms

There are probably too many such $(M,g,I_+,I_-)$ to really expect a 'classification'. For instance, consider the case when a complex manifold $(M,I_+)$ has real dimension $4$, and the $I_+$-holomorphi …
Robert Bryant's user avatar
4 votes

Neighborhood theorem for conical Lagrangian

The answer is 'no', even in the simplest nontrivial case $n=2$, if you assume that the symplectomorphism is to take $C$ to $C'$. (If you don't assume that the symplectomorphism is supposed to take $C …
Robert Bryant's user avatar
9 votes
Accepted

Are holomorphic Lagrangians locally graphs?

The answer is 'yes'. Specifically, the holomorphic version of the Darboux-Weinstein theorem holds, just as it does in the smooth category. In particular, if $L\subset M$ is a holomorphic Lagrangian …
Robert Bryant's user avatar
5 votes

Realizing closed manifolds as Legendrian submanifolds of the standard contact vector space

There are obstructions: For example, if $N^n\subset\mathbb{R}^{2n+1}$ is a Legendrian submanifold, then $\nu$, the normal bundle of $N^n$, is isomorphic to $\tau\oplus TN$, where $\tau$ is the trivia …
Robert Bryant's user avatar
5 votes
Accepted

$\omega$ is a symplectic form then $L^k_{\omega}:\Omega^q(M)\to \Omega^{q+2k}(M)$ is injecti...

The injectivity case is well-known and follows quite easily from the statement (usually attributed to Lefschetz) that $L^k_\omega:\Omega^{n-k}(M)\to \Omega^{n+k}(M)$ is a isomorphism for $0\le k\le n$ …
Robert Bryant's user avatar
21 votes

Asking whether there is a compact Lie group containing affine symplectic group

The answer is 'no', the affine symplectic group cannot appear as a Lie subgroup of any compact Lie group. The reason is that the affine symplectic group contains $\mathrm{SL}(2,\mathbb{R})$ as a Lie …
Robert Bryant's user avatar
4 votes
Accepted

Existence of solution to a system of linear PDEs with boundary conditions

The general solution of your equations in a simply connected domain on which $r_2\not=0$ and $r_1\not=\pm1$ is $$ \beta = \frac12 + \frac1{{(r_1}^2{-}1)}\, \left(\frac{\partial a}{\partial\theta_1}+b( …
Robert Bryant's user avatar
6 votes
Accepted

$2$-Form inducing a non-degenerate form on $\Gamma(T\mathbb{R}^{2n+1})$

The example in $\mathbb{R}^3$ given by $$ \omega = x\,\mathrm{d}y\wedge\mathrm{d}z + y\,\mathrm{d}z\wedge\mathrm{d}x + z\,\mathrm{d}x\wedge\mathrm{d}y, $$ shows that the kernel of $\omega$ need not be …
Robert Bryant's user avatar
15 votes
Accepted

Non-isomorphic compact Kähler manifolds that are biholomorphic, symplectomorphic and isometric

The answer is 'no, not necessarily'. Consider the following example: Let $M=N=\mathbb{CP}^2$, let $(\omega_0,J_0)$ be the standard Fubini-Study Kähler structure on $M$. Now let $f$ be an arbitrary, …
Robert Bryant's user avatar
8 votes
Accepted

Non-symplectomorphic isometric compact Kähler manifolds

The answer to your first question is 'no' and the answer to your second question is 'yes'. A simple example, when $n\ge 2$, is to let $M = \mathbb{R}^{2n}/\Lambda$ where $\Lambda\subset \mathbb{R}^{2n …
Robert Bryant's user avatar
4 votes
Accepted

Name for a class of almost symplectic manifolds

I'm a bit confused by your question, because I believe that, if one defines an $\omega$-Hamiltonian vector field to be a vector field of the form $X_f = \omega^\#(\mathrm{d}f)$ where $f$ is a (smooth) …
Robert Bryant's user avatar
13 votes
Accepted

Which curves are boundary of pseudoholomorphic curves?

The 'moment conditions' that Ben McKay mentions are simply this: A closed curve $C$ in $\mathbb{C}^n$ bounds a compact Riemann surface (which might be singular) if and only if the integral around $C$ …
Robert Bryant's user avatar
10 votes
Accepted

Holomorphic Weinstein Lagrangian neighborhood theorem

A classic example that shows that WLNT doesn't always hold in the holomorphic category is an elliptically fibered $K3$ surface. A K3 surface $S$ is a compact complex symplectic manifold of complex …
Robert Bryant's user avatar
8 votes

Lagrangian surgery

Actually, one can always do a (local) surgery to 'resolve' transverse intersection points of Lagrangian submanifolds, and this works in all dimensions, not just dimension $2$. Here is a sketch of an …
Robert Bryant's user avatar
7 votes
Accepted

The automorphism group of a symplectic symmetric space

The affine group of $(M,\nabla)$ is a Lie group $G$ by Kobayashi's theorem that shows that the automorphism group of any affine connection is a Lie group (see Kobayashi and Nomizu's Foundations of Dif …
Robert Bryant's user avatar

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