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We show that any finitely presented group with an index two subgroup is realized as the fundamental group of a closed smooth non-orientable four-manifold that admits an exotic smooth structure, which is obtained by performing a Gluck twist.…

Geometric Topology · Mathematics 2025-08-27 Rafael Torres

We prove for any positive integer $n$ there exist boundary-sum irreducible ${\mathbb Z}_n$-corks with Stein structure. Here `boundary-sum irreducible' means the manifold is indecomposable with respect to boundary-sum. We also verify that…

Geometric Topology · Mathematics 2017-10-26 Motoo Tange

We prove that every 4-dimensional oriented handlebody without 3- and 4-handles can be modified to admit infinitely many exotic smooth structures, and moreover prove that their genus functions are pairwise equivalent. We furthermore show…

Geometric Topology · Mathematics 2025-12-25 Kouichi Yasui

We provide the first information on diffeotopy groups of exotic smoothings of R^4: For each of uncountably many smoothings, there are uncountably many isotopy classes of self-diffeomorphisms. We realize these by various explicit group…

Geometric Topology · Mathematics 2018-12-03 Robert E. Gompf

We give a brief survey of some facts about homotopy $4$-spheres \cite{a1}, then give a proof that the curious homotopy sphere constructed in \cite{a2} is in fact diffeomorphic to the standard $S^4$, and discuss its relation to infinite…

Geometric Topology · Mathematics 2020-08-21 Selman Akbulut

We show that the classification up to homeomorphism of closed topological nonorientable 4-manifolds with fundamental group of order 2 due to Hambleton-Kreck-Teichner can be used to classify a large set of such 4-manifolds with cyclic…

Geometric Topology · Mathematics 2026-01-09 Rafael Torres

From any 4-dimensional oriented handlebody X without 3- and 4-handles and with b_2>0, we construct arbitrary many compact Stein 4-manifolds which are mutually homeomorphic but not diffeomorphic to each other, so that their topological…

Geometric Topology · Mathematics 2012-05-23 Selman Akbulut , Kouichi Yasui

We introduce and study a class of compact 4-manifolds with boundary that we call protocorks. Any exotic pair of simply connected closed 4-manifolds is related by a protocork twist, moreover, any cork is supported by a protocork. We prove a…

Geometric Topology · Mathematics 2024-03-15 Roberto Ladu

We prove a localization theorem for exotic diffeomorphisms, showing that every diffeomorphism of a compact simply-connected 4-manifold that is isotopic to the identity after stabilizing with one copy of $S^2 \times S^2$, is smoothly…

Geometric Topology · Mathematics 2026-02-27 Vyacheslav Krushkal , Anubhav Mukherjee , Mark Powell , Terrin Warren

A fundamental result in 4-manifold topology asserts that any two exotic smooth structures on a simply-connected, closed 4-manifold differ by a cork twist: the operation of removing a compact, contractible, codimension-zero submanifold and…

Geometric Topology · Mathematics 2026-05-27 Cindy Zhang

We show how to construct absolutely exotic smooth structures on compact 4-manifolds with boundary, including contractible manifolds. In particular, we prove that any compact smooth 4-manifold W with boundary that admits a relatively exotic…

Geometric Topology · Mathematics 2014-12-12 Selman Akbulut , Daniel Ruberman

Let K be the subgroup of the extended mapping class group, Mod(S), generated by Dehn twists about separating curves. Assuming that S is a closed, orientable surface of genus at least 4, we confirm a conjecture of Farb that Comm(K), Aut(K)…

Geometric Topology · Mathematics 2014-11-11 Tara E Brendle , Dan Margalit

We show that for any po sitive integer $m$, there exist order $n$ Stein corks. The boundaries are cyclic branched covers of slice knots embedded in the boundary of corks. By applying these corks to generalized forms, we give a method…

Geometric Topology · Mathematics 2016-02-16 Motoo Tange

We provide an approach to study exotic phenomena in relatively small 4-manifolds that captures many different exotic behaviors under one umbrella. These phenomena include exotic smooth structures on 4-manifolds with $b_2=1$, examples of…

Geometric Topology · Mathematics 2023-04-13 Hokuto Konno , Abhishek Mallick , Masaki Taniguchi

We introduce multisections of smooth, closed 4-manifolds, which generalize trisections to decompositions with more than three pieces. This decomposition describes an arbitrary smooth, closed 4-manifold as a sequence of cut systems on a…

Geometric Topology · Mathematics 2020-10-08 Gabriel Islambouli , Patrick Naylor

Positive Dehn twist products for some elements of finite order in the mapping class group of a 2-dimensional closed, compact, oriented surface $\Sigma_g$, which are rotations of $\Sigma_g$ through $2\pi /p$, are presented. The homeomorphism…

Geometric Topology · Mathematics 2007-05-23 Yusuf Z. Gurtas

We give a topological interpretation of the core group invariant of a surface embedded in S^4. We show that the group is isomorphic to the free product of the fundamental group of the double branch cover of S^4 with the surface as a…

Geometric Topology · Mathematics 2007-05-23 Jozef H. Przytycki , Witold Rosicki

Following McDuff and Tolman's work on toric manifolds [McDT06], we focus on 4-dimensional NEF toric manifolds and we show that even though Seidel's elements consist of infinitely many contributions, they can be expressed by closed formulas.…

Symplectic Geometry · Mathematics 2015-05-07 Sílvia Anjos , Rémi Leclercq

We investigate two specific contractible manifolds (one Stein, and the other non-Stein) whose boundaries have non-trivial mapping class groups. In both cases we show that every diffeomorphism of their boundary extends to a diffeomorphism of…

Geometric Topology · Mathematics 2019-12-30 Selman Akbulut , Daniel Ruberman

This article is concerned with locally flatly immersed surfaces in simply-connected $4$-manifolds where the complement of the surface has fundamental group $\mathbb{Z}$. Once the genus and number of double points are fixed, we classify such…

Geometric Topology · Mathematics 2024-10-08 Anthony Conway , Allison N. Miller