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Jinpeng An

Publications and source records attributed to Jinpeng An.

At least 19 recordsLinked to original sources
arXiv2024

Zimmer's conjecture for non-split semisimple Lie groups

We prove many new cases of Zimmer's conjecture for actions by lattices in non-$\mathbb{R}$-split semisimple Lie groups $G$. By prior arguments, Zimmer's conjecture reduces to studying certain probability measures invariant under a minimal parabolic subgroup for the induced $G$-action. Two techniques are introduced to give lower bounds on the dimension of a manifold $M$ admitting a non-isometric action. First, when the Levi component of the stabilizer of the measure has higher-rank simple factors, cocycle superrigidity provides a lower bound on the dimension of $M$. Second, when certain fiberwise coarse Lyapunov distributions are one-dimensional, a measure rigidity argument provides additional invariance of the measure if the associated root spaces are higher-dimensional.

math.DS↗
arXiv2022

Rigidity of stable Lyapunov exponents and integrability for Anosov maps

Let $f$ be a non-invertible irreducible Anosov map on $d$-torus. We show that if the stable bundle of $f$ is one-dimensional, then $f$ has the integrable unstable bundle, if and only if, every periodic point of $f$ admits the same Lyapunov exponent on the stable bundle with its linearization. For higher-dimensional stable bundle case, we get the same result on the assumption that $f$ is a $C^1$-perturbation of a linear Anosov map with real simple Lyapunov spectrum on the stable bundle. In both cases, this implies if $f$ is topologically conjugate to its linearization, then the conjugacy is smooth on the stable bundle.

math.DS↗
arXiv2021

On the small measure expansion phenomenon in connected noncompact nonabelian groups

Suppose $G$ is a connected noncompact locally compact group, $A,B$ are nonempty and compact subsets of $G$, $μ$ is a left Haar measure on $G$. Assuming that $G$ is unimodular, and $ μ(A^2) < K μ(A) $ with $K>1$ a fixed constant, our first result shows that there is a continuous surjective group homomorphism $χ: G\to L$ with compact kernel, where $L$ is a Lie group with $$\dim(L) \leq \lfloor\log K\rfloor(\lfloor\log K\rfloor+1)/2.$$ We also demonstrate that this dimension bound is sharp, establish the relationship between $A$ and its image under the quotient map, and obtain a more general version of this result for the product set $AB$ without assuming unimodularity. Our second result classifies $G,A,B$ where $A,B$ have nearly minimal expansions (when $G$ is unimodular, this just means $μ(AB)$ is close to $μ(A)+μ(B)$). This answers a question suggested by Griesmer and Tao, and completes the last open case of the inverse Kemperman problem. The proofs of both results involve a new analysis of locally compact group $G$ with bounded $n-h$, where $n-h$ is an invariant of $G$ appearing in the recently developed nonabelian Brunn-Minkowski inequality. We also generalize Ruzsa's distance and related results to possibly nonunimodular locally compact groups.

math.GR↗
arXiv2021

Nondense orbits on homogeneous spaces and applications to geometry and number theory

Let $G$ be a Lie group, $Γ\subset G$ a discrete subgroup, $X=G/Γ$, and $f$ an affine map from $X$ to itself. We give conditions on a submanifold $Z$ of $X$ guaranteeing that the set of points $x\in X$ with $f$-trajectories avoiding $Z$ is hyperplane absolute winning (a property which implies full Hausdorff dimension and is stable under countable intersections). A similar result is proved for one-parameter actions on $X$. This has applications to constructing exceptional geodesics on locally symmetric spaces, and to non-density of the set of values of certain functions at integer points.

math.DS↗
arXiv2020

Divergent trajectories on products of homogeneous spaces

In this paper, we determine the Hausdorff dimension of the set of points with divergent trajectories on the product of certain homogeneous spaces. The flow is allowed to be weighted with respect to the factors in the product space. The result is derived from its counterpart in Diophantine approximation. In doing this, we introduce a notion of jointly singular matrix tuples, and extend the dimension formula for singular matrices to such matrix tuples.

math.DS↗
arXiv2019

Bounded orbits of Diagonalizable Flows on finite volume quotients of products of $SL_2(\mathbb{R})$

We prove a number field analogue of W. M. Schmidt's conjecture on the intersection of weighted badly approximable vectors and use this to prove an instance of a conjecture of An, Guan and Kleinbock. Namely, let $G := SL_2(\mathbb{R}) \times \dots \times SL_2(\mathbb{R}) $ and $Γ$ be a lattice in $G$. We show that the set of points on $G/Γ$ whose forward orbits under a one parameter Ad-semisimple subsemigroup of $G$ are bounded, form a hyperplane absolute winning set.

math.DS↗
arXiv2014

Badly approximable points on planar curves and winning

For any i,j>0 with i+j =1, let Bad(i,j) denote the set of points (x,y) \in R^2 such that max \{ ||qx||^{1/i}, \, ||qy||^{1/j} \} > c/q for some positive constant c = c(x,y) and all q in N. We show that \Bad(i,j) \cap C is winning in the sense of Schmidt games for a large class of planar curves C, namely, everywhere non-degenerate planar curves and straight lines satisfying a natural Diophantine condition. This strengthens recent results solving a problem of Davenport from the sixties. In short, within the context of Davenport's problem, the winning statement is best possible. Furthermore, we obtain the inhomogeneous generalizations of the winning results for planar curves and lines and also show that the inhomogeneous form of Bad(i,j) is winning for two dimensional Schmidt games.

math.NT↗
arXiv2014

Two-dimensional badly approximable vectors and Schmidt's game

We prove that for any pair $(s,t)$ of nonnegative numbers with $s+t=1$, the set of two-dimensional $(s,t)$-badly approximable vectors is winning for Schmidt's game. As a consequence, we give a direct proof of Schmidt's conjecture using his game.

math.NT↗
arXiv2013

Remarks on minimal sets and conjectures of Cassels, Swinnerton-Dyer, and Margulis

We prove that a hypothesis of Cassels, Swinnerton-Dyer, recast by Margulis as statement on the action of the diagonal group $A$ on the space of unimodular lattices, is equivalent to several assertions about minimal sets for this action. More generally, for a maximal $\mathbb{R}$-diagonalizable subgroup $A$ of a reductive group $G$ and a lattice $Γ$ in $G$, we give a sufficient condition for a compact $A$-minimal subset $Y$ of $G/Γ$ to be of a simple form, which is also necessary if $G$ is $\mathbb{R}$-split. We also show that the stabilizer of $Y$ has no nontrivial connected unipotent subgroups.

math.DS↗
arXiv2012

Badziahin-Pollington-Velani's theorem and Schmidt's game

We prove that for any $s,t\ge0$ with $s+t=1$ and any $θ\in\mathbb{R}$ with $\inf_{q\in\mathbb{N}}q^{\frac{1}{s}}\|qθ\|>0$, the set of $y\in\mathbb{R}$ for which $(θ,y)$ is $(s,t)$-badly approximable is 1/2-winning for Schmidt's game. As a consequence, we remove a technical assumption in a recent theorem of Badziahin-Pollington-Velani on simultaneous Diophantine approximation.

math.NT↗
arXiv2011

Rigid geometric structures, isometric actions, and algebraic quotients

By using a Borel density theorem for algebraic quotients, we prove a theorem concerning isometric actions of a Lie group $G$ on a smooth or analytic manifold $M$ with a rigid $\mathrm{A}$-structure $σ$. It generalizes Gromov's centralizer and representation theorems to the case where $R(G)$ is split solvable and $G/R(G)$ has no compact factors, strengthens a special case of Gromov's open dense orbit theorem, and implies that for smooth $M$ and simple $G$, if Gromov's representation theorem does not hold, then the local Killing fields on $\widetilde{M}$ are highly non-extendable. As applications of the generalized centralizer and representation theorems, we prove (1) a structural property of $\mathrm{Iso}(M)$ for simply connected compact analytic $M$ with unimodular $σ$, (2) three results illustrating the phenomena that if $G$ is split solvable and large then $π_1(M)$ is also large, and (3) two fixed point theorems for split solvable $G$ and compact analytic $M$ with non-unimodular $σ$.

math.DG↗
arXiv2009

Zero patterns and unitary similarity

A subspace of the space, L(n), of traceless complex $n\times n$ matrices can be specified by requiring that the entries at some positions $(i,j)$ be zero. The set, $I$, of these positions is a (zero) pattern and the corresponding subspace of L(n) is denoted by $L_I(n)$. A pattern $I$ is universal if every matrix in L(n) is unitarily similar to some matrix in $L_I(n)$. The problem of describing the universal patterns is raised, solved in full for $n\le3$, and partial results obtained for $n=4$. Two infinite families of universal patterns are constructed. They give two analogues of Schur's triangularization theorem.

math.RT↗
arXiv2009

Universal subspaces for compact Lie groups

For a representation of a connected compact Lie group G in a finite dimensional real vector space U and a subspace V of U, invariant under a maximal torus of G, we obtain a sufficient condition for V to meet all G-orbits in U, which is also necessary in certain cases. The proof makes use of the cohomology of flag manifolds and the invariant theory of Weyl groups. Then we apply our condition to the conjugation representations of U(n), Sp(n), and SO(n) in the space of $n\times n$ matrices over C, H, and R, respectively. In particular, we obtain an interesting generalization of Schur's triangularization theorem.

math.RT↗
arXiv2009

Nonabelian cohomology of compact Lie groups

Given a Lie group $G$ with finitely many components and a compact Lie group A which acts on $G$ by automorphisms, we prove that there always exists an A-invariant maximal compact subgroup K of G, and that for every such K, the natural map $H^1(A,K)\to H^1(A,G)$ is bijective. This generalizes a classical result of Serre [6] and a recent result in [1].

math.GR↗
arXiv2008

Nonabelian harmonic analysis and functional equations on compact groups

Making use of nonabelian harmonic analysis and representation theory, we solve the functional equation $$f_1(xy)+f_2(yx)+f_3(xy^{-1})+f_4(y^{-1}x)=f_5(x)f_6(y)$$ on arbitrary compact groups. The structure of its general solution is completely described. Consequently, several special cases of the above equation, in particular, the Wilson equation and the d'Alembert long equation, are solved on compact groups.

math.FA↗
arXiv2007

Holomorphic harmonic analysis on complex reductive groups

We define the holomorphic Fourier transform of holomorphic functions on complex reductive groups, prove some properties like the Fourier inversion formula, and give some applications. The definition of the holomorphic Fourier transform makes use of the notion of $K$-admissible measures. We prove that $K$-admissible measures are abundant, and the definition of holomorphic Fourier transform is independent of the choice of $K$-admissible measures.

math.GR↗
arXiv2007

Holder stability of diffeomorphisms

We prove that a $C^2$ diffeomorphism $f$ of a compact manifold $M$ satisfies Axiom A and the strong transversality condition if and only if it is Hölder stable, that is, any $C^1$ diffeomorphism $g$ of $M$ sufficiently $C^1$ close to $f$ is conjugate to $f$ by a homeomorphism which is Hölder on the whole manifold.

math.DS↗