arXiv subjects

Daciberg Lima Gonçalves

Publications and source records attributed to Daciberg Lima Gonçalves.

At least 19 recordsLinked to original sources

arXiv2026

A study of $n$-valued non-split maps and applications

For a given $n$-valued map, there exists a suitable minimal covering of the domain such that the composition of this covering with the map yields a split map, composed of $n$ single-valued maps, called the lift factors. Using the group action of the deck-transformation group we construct intermediate covering spaces as well as intermediate configuration spaces, allowing the original map to lift to these spaces, building a tower to illustrate at which level the lift factors split off. We then display two applications of these new tools. The first is to derive results concerning the Borsuk-Ulam property for certain coverings of the tower. The second is to obtain a sharp formula for the Nielsen number of an $n$-valued non-split map, using the coincidence number of specific single-valued maps that arise in the lifts of the tower.

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arXiv2025

The Splitting of Generalisations of the Fadell-Neuwirth short exact sequence

We study some generalisations to mixed braid groups of the Fadell-Neuwirth short exact sequence and the possible splitting of this sequence. In certain cases, we determine conditions under which the projection from the mixed braid group $B_{n_{1},\ldots,n_{k}}(M)$ to $B_{n_{1},\ldots, n_{k-q}}(M)$ admits a section, where $M$ is either the torus or the Klein bottle, $n_{1}, \ldots, n_{k},q \in \mathbb{N}$, and $1\leq q \leq k-1$. For $k\geq 2$ and $q=k-1$, we show that this projection admits a section if and only if $n_{1}$ divides $n_{i}$ for all $i=2,\ldots, k$. We present some partial conclusions in the case $k\geq 3$ and $q=1$. To obtain our results, we compute and make use of suitable mixed braid groups of $M$, as well as certain key quotients that play a central rôle in our analysis.

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arXiv2025

The R$_{\infty}$-property for braid groups over orientable surfaces

Let $Σ_{g,p}$ be an orientable surface of genus $g$ and of finite type without boundary (i.e. an orientable closed surface with a finite number $p$ of points removed). In this paper we study the R$_{\infty}$-property for the surface pure braid groups $P_n(Σ_{g,p})$ as well as for the full surface braid groups $B_n(Σ_{g,p})$. We show that, with few exceptions, these groups have the R$_{\infty}$-property.

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arXiv2024

Borsuk--Ulam property for graphs II: The $\mathbb{Z}_n$-action

For a finite group $H$ and connected topological spaces $X$ and $Y$ such that $X$ is endowed with a free left $H$-action $τ$, we provide a geometric condition in terms of the existence of a commutative diagram of spaces (arising from the triple $(X,Y;τ)$) to decide whether the Borsuk--Ulam property holds for based homotopy classes $α\in[X,Y]_0$, as well as for free homotopy classes $α\in[X,Y]$. Here, a homotopy class $α$ is said to satisfy the Borsuk--Ulam property if, for each of its representatives $f\inα$, there exists an $H$-orbit where $f$ fails to be injective. Our geometric characterization is attained by constructing an $H$-equivariant map from $X$ to the classical configuration space $F_{|H|}(Y)$. We derive an algebraic condition from the geometric characterisation, and show that the former one is in fact equivalent to the latter one when $X$ and $Y$ are aspherical. We then specialize to the 1-dimensional case, i.e., when $X$ is an arbitrary connected graph, $H$ is cyclic, and $Y$ is either an interval, a circle, or their wedge sum. The graph-braid-group ingredient in our characterizations is then effectively controlled through the use of discrete Morse theory.

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arXiv2024

Characteristic subgroups and the R$_\infty$-property for virtual braid groups

Let $n\geq 2$. Let $VB_n$ (resp. $VP_n$) denote the virtual braid group (resp. virtual pure braid group), let $WB_n$ (resp. $WP_n$) denote the welded braid group (resp. welded pure braid group) and let $UVB_n$ (resp. $UVP_n$) denote the unrestricted virtual braid group (resp. unrestricted virtual pure braid group). In the first part of this paper we prove that, for $n\geq 4$, the group $VP_n$ and for $n\geq 3$ the groups $WP_n$ and $UVP_n$ are characteristic subgroups of $VB_n$, $WB_n$ and $UVB_n$, respectively. In the second part of the paper we show that, for $n\geq 2$, the virtual braid group $VB_n$, the unrestricted virtual pure braid group $UVP_n$, and the unrestricted virtual braid group $UVB_n$ have the R$_\infty$-property. As a consequence of the technique used for few strings we also prove that, for $n=2,3,4$, the welded braid group $WB_n$ has the R$_\infty$-property and that for $n=2$ the corresponding pure braid groups have the R$_\infty$-property. On the other hand for $n\geq 3$ it is unknown if the R$_\infty$-property holds or not for the virtual pure braid group $VP_n$ and the welded pure braid group $WP_n$.

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arXiv2023

Index and Sectional Category

Let $G$ be a finite group with order $|G|=\ell$ and $2\leq q\leq \ell$. For a free $G$-space $X$, we introduce a notion of $q$-th index of $(X,G)$, denoted by $\text{ind}_q(X,G)$. Our concept is relevant in the Borsuk-Ulam theory. We draw general estimates for the $q$-th index in terms of the sectional category of the quotient map $X\to X/G$, denoted by $\text{secat}(X\to X/G)$. This property connects a standard problem in Borsuk-Ulam theory to current research trends in sectional category. Under certain hypothesis we observed that $\text{secat}(X\to X/G)=\text{ind}_2(X,G)+1$. As an application of our results, we present new results in Borsuk-Ulam theory and sectional category.

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arXiv2023

Decomposability of minimal defect branched coverings over the projective plane

In this paper we characterize primitive branched coverings with minimal defect over the projective plane with respect to the properties decomposable and indecomposable. This minimality is achieved when the covering surface is also the projective plane, which corresponds to the last case to be solved. As a consequence, we have extended the family of realisations of branched coverings on the projective plane and established a type of generalisation of results on primitive permutation groups.

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arXiv2023

The Borsuk-Ulam property for homotopy classes on bundles, parametrized braids groups and applications for surfaces bundles

Let $M$ and $N$ be fiber bundles over the same base $B$, where $M$ is endowed with a free involution $τ$ over $B$. A homotopy class $δ\in [M,N]_{B}$ (over $B$) is said to have the Borsuk-Ulam property with respect to $τ$ if for every fiber-preserving map $f\colon M \to N$ over $B$ which represents $δ$ there exists a point $x \in M$ such that $f(τ(x)) = f(x)$. In the cases that $B$ is a $K(π,1)$-space and the fibers of the projections $M \to B$ and $N \to B$ are $K(π,1)$ closed surfaces $S_M$ and $S_N$, respectively, we show that the problem of decide if a homotopy class of a fiber-preserving map $f\colon M \to N$ over $B$ has the Borsuk-Ulam property is equivalent of an algebraic problem involving the fundamental groups of $M$, the orbit space of $M$ by $τ$ and a type of generalized braid groups of $N$ that we call parametrized braid groups. As an application, we determine the homotopy classes of self fiber-preserving maps of some 2-torus bundles over $\mathbb{S}^1$ that satisfy the Borsuk-Ulam property with respect to certain involutions $τ$ over $\mathbb{S}^1$.

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arXiv2022

Borsuk-Ulam property for graphs

For finite connected graphs $Γ$ and $G$, with $Γ$ admitting a free involution $τ$, we characterize the based homotopy classes $α\in[Γ,G]$ for which the Borsuk-Ulam property holds in the sense of Gonçalves, Guaschi and Casteluber-Laass, i.e., the homotopy classes $α$ so that each of its representatives $f\inα$ satisfies $f(x) = f(τ\cdot x)$ for some $x\inΓ$. This is attained through a graph-braid-group perspective aided by the use of discrete Morse theory.

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arXiv2022

Free cyclic actions on surfaces and the Borsuk-Ulam theorem

Let $M$ and $N$ be topological spaces, let $G$ be a group, and let $τ\colon\thinspace G \times M \to M$ be a proper free action of $G$. In this paper, we define a Borsuk-Ulam-type property for homotopy classes of maps from $M$ to $N$ with respect to the pair $(G,τ)$ that generalises the classical antipodal Borsuk-Ulam theorem of maps from the $n$-sphere $\mathbb{S}^n$ to $\mathbb{R}^n$. In the cases where $M$ is a finite pathwise-connected CW-complex, $G$ is a finite, non-trivial Abelian group, $τ$ is a proper free cellular action, and $N$ is either $\mathbb{R}^2$ or a compact surface without boundary different of $\mathbb{S}^2$ and $\mathbb{RP}^2$, we give an algebraic criterion involving braid groups to decide whether a free homotopy class $β\in [M,N]$ has the Borsuk-Ulam property. As an application of this criterion, we consider the case where $M$ is a compact surface without boundary equipped with a free action $τ$ of the finite cyclic group $\mathbb{Z}_n$. In terms of the orientability of the orbit space $M_τ$ of $M$ by the action $τ$, the value of $n$ modulo $4$ and a certain algebraic condition involving the first homology group of $M_τ$, we are able to determine if the single homotopy class of maps from $M$ to $\mathbb{R}^2$ possesses the Borsuk-Ulam property with respect to $(\mathbb{Z}_n,τ)$. Finally, we give some examples of surfaces on which the symmetric group acts, and for these cases, we obtain some partial results regarding the Borsuk-Ulam property for maps whose target is $\mathbb{R}^2$.

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arXiv2021

The Borsuk-Ulam property for homotopy classes of maps between the torus and the Klein bottle -- part 2

Let $M$ be a topological space that admits a free involution $τ$, and let $N$ be a topological space. A homotopy class $β\in [ M,N ]$ is said to have the Borsuk-Ulam property with respect to $τ$ if for every representative map $f: M \to N$ of $β$, there exists a point $x \in M$ such that $f(τ(x))= f(x)$. In this paper, we determine the homotopy class of maps from the $2$-torus $T^2$ to the Klein bottle $K^2$ that possess the Borsuk-Ulam property with respect to any free involution of $T^2$ for which the orbit space is $K^2$. Our results are given in terms of a certain family of homomorphisms involving the fundamental groups of $T^2$ and $K^2$. This completes the analysis of the Borsuk-Ulam problem for the case $M=T^2$ and $N=K^2$, and for any free involution $τ$ of $T^2$.

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arXiv2021

Crystallographic groups and flat manifolds from surface braid groups

Let $M$ be a compact surface without boundary, and $n\geq 2$. We analyse the quotient group $B_n(M)/Γ_2(P_n(M))$ of the surface braid group $B_{n}(M)$ by the commutator subgroup $Γ_2(P_n(M))$ of the pure braid group $P_{n}(M)$. If $M$ is different from the $2$-sphere $\mathbb{S}^2$, we prove that $B_n(M)/Γ_2(P_n(M))$ is isomorphic rho $P_n(M)/Γ_2(P_n(M)) \rtimes_φ S_n$, and that $B_n(M)/Γ_2(P_n(M))$ is a crystallographic group if and only if $M$ is orientable. If $M$ is orientable, we prove a number of results regarding the structure of $B_n(M)/Γ_2(P_n(M))$. We characterise the finite-order elements of this group, and we determine the conjugacy classes of these elements. We also show that there is a single conjugacy class of finite subgroups of $B_n(M)/Γ_2(P_n(M))$ isomorphic either to $S_n$ or to certain Frobenius groups. We prove that crystallographic groups whose image by the projection $B_n(M)/Γ_2(P_n(M))\to S_n$ is a Frobenius group are not Bieberbach groups. Finally, we construct a family of Bieberbach subgroups $\tilde{G}_{n,g}$ of $B_n(M)/Γ_2(P_n(M))$ of dimension $2ng$ and whose holonomy group is the finite cyclic group of order $n$, and if $\mathcal{X}_{n,g}$ is a flat manifold whose fundamental group is $\tilde{G}_{n,g}$, we prove that it is an orientable Kähler manifold that admits Anosov diffeomorphisms.

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arXiv2020

Strongly surjective maps from certain two-complexes with trivial top-cohomology onto the projective plane

For the model two-complex $K$ of the group presentation $\mathcal{P}=\langle x,y\,|\,x^{k+1}yxy \rangle$, with $k\geq1$ odd, we describe representatives for all free and based homotopy classes of maps from $K$ into the real projective plane and we classify the homotopy classes containing only surjective maps. With this approach we get an answer, for maps into the real projective plane, for a classical question in topological root theory, which is known so far, in dimension two, only for maps into the sphere, the torus and the Klein bottle. The answer follows by proving that for all $k\geq1$ odd, $H^2(K;mathbb{Z})=0$ and, for $k\geq3$ odd, there exist maps from $K$ into the real projective plane which are strongly surjective. For $k=1$, there is no such a strongly surjective map. 55N25, 57M20.

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arXiv2020

The R$_\infty$ property for pure Artin braid groups

In this paper we prove that all pure Artin braid groups $P_n$ ($n\geq 3$) have the $R_\infty$ property. In order to obtain this result, we analyse the naturally induced morphism $\operatorname{\text{Aut}}(P_n) \to \operatorname{\text{Aut}}(Γ_2 (P_n)/Γ_3(P_n))$ which turns out to factor through a representation $ρ\colon S_{n+1} \to \operatorname{\text{Aut}}(Γ_2 (P_n)/Γ_3(P_n))$. We can then use representation theory of the symmetric groups to show that any automorphism $α$ of $P_n$ acts on the free abelian group $Γ_2 (P_n)/Γ_3(P_n)$ via a matrix with an eigenvalue equal to 1. This allows us to conclude that the Reidemeister number $R(α)$ of $α$ is $\infty$.

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arXiv2019

The Borsuk-Ulam property for homotopy classes of maps between the torus and the Klein bottle

Let $M$ be a topological space that admits a free involution $τ$, and let $N$ be a topological space. A homotopy class $β\in [ M,N ]$ is said to have {\it the Borsuk-Ulam property with respect to $τ$} if for every representative map $f: M \to N$ of $β$, there exists a point $x \in M$ such that $f(τ(x))= f(x)$. In this paper, we determine the homotopy classes of maps from the $2$-torus $T^2$ to the Klein bottle $K^2$ that possess the Borsuk-Ulam property with respect to a free involution $τ_1$ of $T^2$ for which the orbit space is $T^2$. Our results are given in terms of a certain family of homomorphisms involving the fundamental groups of $T^2$ and $K^2$.

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arXiv2019

The group Aut and Out of the fundamental group of a closed Sol 3-manifold

Let $E$ be the fundamental group of a closed Sol 3-manifold. We describe the groups $Aut(E)$ and $Out(E)$. We first consider the case where $E$ is the fundamental group of a torus bundle, and then the case where $E$ is the fundamental group of a closed Sol 3-manifold which is not a torus bundle. The groups are described in terms of some iterated semi-direct products of well known groups, where one exception is for $Out(E)$ for some $E$'s, in which case $Out(E)$ is described as an extension and a presentation is given.

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arXiv2018

Embeddings of finite groups in $B_n/Γ_k(P_n)$ for $k=2, 3$

Let $n \geq 3$. In this paper, we study the problem of whether a given finite group $G$ embeds in a quotient of the form $B_n/Γ_k(P_n)$, where $B_n$ is the $n$-string Artin braid group, $k \in \{2, 3\}$, and $\{Γ_l(P_n)\}_{l\in \mathbb{N}}$ is the lower central series of the $n$-string pure braid group $P_n$. Previous results show that a necessary condition for such an embedding to exist is that $|G|$ is odd (resp. is relatively prime with $6$) if $k=2$ (resp. $k=3$), where $|G|$ denotes the order of $G$. We show that any finite group $G$ of odd order (resp. of order relatively prime with $6$) embeds in $B_{|G|}/Γ_2(P_{|G|})$ (resp. in $B_{|G|}/Γ_3(P_{|G|})$). The result in the case of $B_{|G|}/Γ_2(P_{|G|})$ has been proved independently by Beck and Marin. One may then ask whether $G$ embeds in a quotient of the form $B_n/Γ_k(P_n)$, where $n < |G|$ and $k \in \{2, 3\}$. If $G$ is of the form $\mathbb{Z}_{p^r} \rtimes_θ \mathbb{Z}_d$, where the action $θ$ is injective, $p$ is an odd prime (resp. $p \geq 5$ is prime) $d$ is odd (resp. $d$ is relatively prime with $6$) and divides $p-1$, we show that $G$ embeds in $B_{p^r}/Γ_2(P_{p^r})$ (resp. in $B_{p^r}/Γ_3(P_{p^r})$). In the case $k=2$, this extends a result of Marin concerning the embedding of the Frobenius groups in $B_n/Γ_2(P_n)$, and is a special case of another result of Beck and Marin. Finally, we construct an explicit embedding in $B_9/Γ_2(P_9)$ of the two non-Abelian groups of order $27$, namely the semi-direct product $\mathbb{Z}_9 \rtimes \mathbb{Z}_3$, where the action is given by multiplication by $4$, and the Heisenberg group mod $3$.

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arXiv2018

Lower central series, surface braid groups, surjections and permutations

Generalising previous results on classical braid groups by Artin and Lin, we determine the values of m, n $\in$ N for which there exists a surjection between the n-and m-string braid groups of an orientable surface without boundary. This result is essentially based on specific properties of their lower central series, and the proof is completely combinatorial. We provide similar but partial results in the case of orientable surfaces with boundary components and of non-orientable surfaces without boundary. We give also several results about the classification of different representations of surface braid groups in symmetric groups.

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