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Zhongzi Wang

Publications and source records attributed to Zhongzi Wang.

25 records · Page 2Linked to original sources
arXiv2023

Maps from 3-manifolds to 4-manifolds that induce isomorphisms on $π_1$

In this paper, we prove that any closed orientable 3-manifold $M$ other than $\#^k S^1\times S^2$ and $S^3$ satisfies the following properties: (1) For any compact orientable 4-manifold $N$ bounded by $M$, the inclusion does not induce an isomorphism on their fundamental groups $π_1$. (2) For any map $f:M\to N$ from $M$ to a closed orientable 4-manifold $N$, $f$ does not induce an isomorphism on $π_1$. Relevant results on higher dimensional manifolds are also obtained.

math.GT↗
arXiv2022

Extending periodic maps on surfaces over the 4-sphere

Let $F_g$ be the closed orientable surface of genus $g$. We address the problem to extend torsion elements of the mapping class group ${\mathcal{M}}(F_g)$ over the 4-sphere $S^4$. Let $w_g$ be a torsion element of maximum order in ${\mathcal{M}}(F_g)$. Results including: (1) For each $g$, $w_g$ is periodically extendable over $S^4$ for some non-smooth embedding $e: F_g\to S^4$, and not periodically extendable over $S^4$ for any smooth embedding $e: F_g\to S^4$. (2) For each $g$, $w_g$ is extendable over $S^4$ for some smooth embedding $e: F_g\to S^4$ if and only if $g=4k, 4k+3$. (3) Each torsion element of order $p$ in ${\mathcal{M}}(F_g)$ is extendable over $S^4$ for some smooth embedding $e: F_g\to S^4$ if either (i) $p=3^m$ and $g$ is even; or (ii) $p=5^m$ and $g\ne 4k+2$; or (iii) $p=7^m$. Moreover the conditions on $g$ in (i) and (ii) can not be removed .

math.GT↗
arXiv2022

Realising sets of integers as mapping degree sets

Given two closed oriented manifolds $M,N$ of the same dimension, we denote the set of degrees of maps from $M$ to $N$ by $D(M,N)$. The set $D(M,N)$ always contains zero. We show the following (non-)realisability results: (i) There exists an infinite subset $A$ of $\mathbb Z$ containing $0$ which cannot be realised as $D(M,N)$, for any closed oriented $n$-manifolds $M,N$. (ii) Every finite arithmetic progression of integers containing $0$ can be realised as $D(M,N)$, for some closed oriented $3$-manifolds $M,N$. (iii) Together with $0$, every finite geometric progression of positive integers starting from $1$ can be realised as $D(M,N)$, for some closed oriented manifolds $M,N$.

math.GT↗
arXiv2022

Minimal Euler Characteristics of 4-manifolds with 3-manifold groups

Let $π=π_1(M)$ for a compact 3-manifold $M$, and let $χ_4$, $p$ and $q^*$ be the invariants of Hausmann-Weinberger, Kotschick and Hillman respectively. For certain class of compact 3-manifolds $M$, including all those not containing two-sided $RP^2$, we determine $χ_4(π)$. We address when does $χ_4(π)=p(π)$, when does $χ_4(π)=q^*(π)$, and answer a question raised by Hillman.

math.GT↗
arXiv2022

Equivariant embeddings of manifolds into Euclidean spaces

Suppose a finite group $G$ acts on a manifold $M$. By a theorem of Mostow, also Palais, there is a $G$-equivariant embedding of $M$ into the $m$-dimensional Euclidean space $\RR^{m}$ for some $m$. We are interested in some explicit bounds of such $m$. First we provide an upper bound: there exists a $G$-equivariant embedding of $M$ into $\RR^{d|G|+1}$, where $|G|$ is the order of $G$ and $M$ embeds into $\RR^d$. Next we provide a lower bound for finite cyclic group action $G$: If there are $l$ points having pairwise co-prime lengths of $G$-orbits greater than $1$ and there is a $G$-equivariant embedding of $M$ into $\RR^{m}$, then $m\ge 2l$. Some applications to surfaces are given.

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