论文标题
几何复杂性理论 - 稳定点的投影限制的代数方法
Geometric Complexity Theory -- Lie Algebraic Methods for Projective Limits of Stable Points
论文作者
论文摘要
令$ g $为一个连接的还原组,该组作用于复杂的矢量空间$ v $和投射空间$ {\ mathbb p} v $。令$ x \在v $中,$ {\ cal H} \ subseteq {\ cal g} $为其稳定器的lie代数。我们的目标是了解点$ [y] $,以及在$ [x] $附近发生的稳定器。我们在合适的$ x $社区上构建一个显式$ {\ cal G} $ - 我们称其为$ x $的本地型号。我们表明,$ x $附近的点稳定器的代数为$ {\ cal H} $的子空间。当$ {\ cal h} $还原时,这些是$ {\ cal H} $的子代理。如果关闭了$ x $的轨道,则也从Luna的定理中出发。我们的构造涉及与$ x $相连的地图。我们将本地型号应用于表单,当表格$ g $从表格$ f $获得作为一个参数族的领先术语中,该家族在$ f $上发挥作用。我们表明,$ f $的稳定剂是$ {\ cal k} $的变平$ {\ cal k} _0 $ of $ f $的稳定剂,它作为$ {\ cal H} $的subgerbra,稳定器$ g $。我们专门研究$ f $的情况,其$ sl(x)$ - 轨道是仿射的,$ g $的轨道为co-Dimension $ 1 $。我们表明(i)$ {\ cal h} $具有非常简单的结构,或者(ii)$ {\ cal k} $的元素也可以稳定$ g $和出口的切线。接下来,我们将其应用于伴随动作。我们表明,对于一般矩阵$ x $,其投影轨道闭合(在共轭下)中的nilpotent矩阵的签名由$ x $的频谱的多样性数据确定。最后,我们制定了使用局部微分几何形状的优化问题,以从$ y $到其限制点$ x $找到路径问题的路径问题。我们的研究是由第二作者和Ketan Mulmuley提出的几何复杂性理论的动机。
Let $G$ be a connected reductive group acting on a complex vector space $V$ and projective space ${\mathbb P}V$. Let $x\in V$ and ${\cal H}\subseteq {\cal G}$ be the Lie algebra of its stabilizer. Our objective is to understand points $[y]$, and their stabilizers which occur in the vicinity of $[x]$. We construct an explicit ${\cal G}$-action on a suitable neighbourhood of $x$, which we call the local model at $x$. We show that Lie algebras of stabilizers of points in the vicinity of $x$ are parameterized by subspaces of ${\cal H}$. When ${\cal H}$ is reductive these are Lie subalgebras of ${\cal H}$. If the orbit of $x$ is closed this also follows from Luna's theorem. Our construction involves a map connected to the local curvature form at $x$. We apply the local model to forms, when the form $g$ is obtained from the form $f$ as the leading term of a one parameter family acting on $f$. We show that there is a flattening ${\cal K}_0$ of ${\cal K}$, the stabilizer of $f$ which sits as a subalgebra of ${\cal H}$, the stabilizer $g$. We specialize to the case of forms $f$ whose $SL(X)$-orbits are affine, and the orbit of $g$ is of co-dimension $1$. We show that (i) either ${\cal H}$ has a very simple structure, or (ii) conjugates of the elements of ${\cal K}$ also stabilize $g$ and the tangent of exit. Next, we apply this to the adjoint action. We show that for a general matrix $X$, the signatures of nilpotent matrices in its projective orbit closure (under conjugation) are determined by the multiplicity data of the spectrum of $X$. Finally, we formulate the path problem of finding paths with specific properties from $y$ to its limit points $x$ as an optimization problem using local differential geometry. Our study is motivated by Geometric Complexity Theory proposed by the second author and Ketan Mulmuley.