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.
Cross-projective representations of pairs of anticommutative algebras, alloys and finite-dimensional irreducible representations of some infinite-dimensional Lie algebras
Support varieties and modules of finite projective dimension for modular Lie superalgebras (with an appendix on homological dimensions over Noether Algebras by Luchezar L. Avramov and Srikanth B. Iyengar)
Additive invariants of toric and twisted projective homogeneous varieties via noncommutative motives
I. Panin在90年代证明了扭曲投射齐次簇的代数K理论可以用中心单代数代数来表示。后来，Merkurjev和Panin将复曲面簇的代数K理论描述为可分代数的代数K理论的直接和项。本文利用最近的非对易动机理论，将Panin和Merkurjev-Panin计算从代数K理论推广到所有的加法不变量.作为第一个应用，我们充分计算的循环同调（及其所有的变种）扭曲的投射齐次品种。作为第二个应用，我们证明了一个扭曲的投射齐次簇的非交换动机是平凡的当且仅当相关的中心单代数的Brauer类是平凡的。在此过程中，我们构造了一个完全忠实的张量函子，从Merkurjev-Panin的motivic范畴到Kontsevich的非交换Chow motives范畴，这是独立的兴趣。
