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We construct Anosov diffeomorphisms on manifolds that are homeomorphic to infranilmanifolds yet have exotic smooth structures. These manifolds are obtained from standard infranilmanifolds by connected summing with certain exotic spheres.…

Dynamical Systems · Mathematics 2014-02-26 F. Thomas Farrell , Andrey Gogolev

In this article, we construct infinitley many simply connected, nonsymplectic and pairwise nondiffeomorphic 4-manifolds starting from E(n) and applying the sequence of knot surgery, ordinary blowups and rational blowdown. We also compute…

Geometric Topology · Mathematics 2007-05-23 Anar Akhmedov

We study smooth, proper embeddings of noncompact surfaces in 4-manifolds, focusing on exotic planes and annuli, i.e., embeddings pairwise homeomorphic to the standard embeddings of R^2 and R^2-int D^2 in R^4. We encounter two uncountable…

Geometric Topology · Mathematics 2025-01-08 Robert E. Gompf

Let $X$ be a compact, oriented, smooth, simply-connected $4$-manifold. The mapping class group of $X$ is defined as the group of smooth isotopy classes of diffeomorphisms of $X$. The Torelli group of $X$ is the subgroup of the mapping class…

Geometric Topology · Mathematics 2025-11-19 David Baraglia , Joshua Tomlin

We show that $\mathbb{C}^2$ contains pairs of properly embedded, smooth complex curves that are isotopic through homeomorphisms but not diffeomorphisms of $\mathbb{C}^2$. The construction is based on realizing corks as branched covers of…

Geometric Topology · Mathematics 2021-07-15 Kyle Hayden

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

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 construct the first exotic $\mathbb C \mathbb P^2 \# 4 \overline{\mathbb C \mathbb P^2}$ by means of rational blowdowns. Similarly, we construct the first exotic $3\mathbb C \mathbb P^2 \# b^- \overline{\mathbb C \mathbb P^2}$ for…

Algebraic Geometry · Mathematics 2022-11-24 Javier Reyes , Giancarlo Urzúa

In this paper, we construct cw-expansive homeomorphisms on compact surfaces of genus greater than or equal to zero with a fixed point whose local stable set is connected but not locally connected. This provides an affirmative answer to…

Dynamical Systems · Mathematics 2026-01-01 Alberto Sarmiento , Douglas Danton , Viviane Pardini Valério

We build a non-compact, orientable, hyperbolic four-manifold of finite volume that does not admit any spin structure.

Geometric Topology · Mathematics 2026-04-28 Stefano Riolo , Edoardo Rizzi

In this paper we study smooth structures on closed oriented 4-manifolds with fundamental group Z_2 and definite intersection form. We construct infinitely many irreducible, smooth, oriented, closed, definite four-manifolds with fundamental…

Geometric Topology · Mathematics 2023-10-26 András I. Stipsicz , Zoltán Szabó

We introduce a general procedure called `reverse engineering' that can be used to construct infinite families of smooth 4-manifolds in a given homeomorphism type. As one of the applications of this technique, we produce an infinite family…

Geometric Topology · Mathematics 2014-10-01 Ronald Fintushel , B. Doug Park , Ronald J. Stern

We show that the group of smooth homotopy $7$-spheres acts freely on the set of smooth manifold structures on a topological manifold $M$ which is homotopy equivalent to the real projective $7$-space. We classify, up to diffeomorphism, all…

Geometric Topology · Mathematics 2017-08-22 Ramesh Kasilingam

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

This paper provides a diffeomorphism classification of smooth manifolds homeomorphic to the complex projective space $\mathbb{C}P^m$ for $m \in \{5, 6, 7, 8\}$. The classification is obtained by computing the group of concordance classes of…

Algebraic Topology · Mathematics 2026-05-01 Ramesh Kasilingam

We show an example of an embedded copy of 5RP^2 in the four-sphere which is topologically standard but smoothly knotted, i.e. smoothly not isotopic to the standard embedding.

Geometric Topology · Mathematics 2024-06-26 Gordana Matić , Ferit Öztürk , Javier Reyes , András I. Stipsicz , Giancarlo Urzúa

Every smooth homotopy 4-sphere is diffeomorphic to the 4-sphere.

Geometric Topology · Mathematics 2023-09-06 Akio Kawauchi

In [2], the first author constructed the first known examples of exotic minimal symplectic $\CP#5\CPb$ and minimal symplectic 4-manifold that is homeomorphic but not diffeomorphic to $3\CP#7\CPb$. The construction in [2] uses Y. Matsumoto's…

Geometric Topology · Mathematics 2015-06-02 Anar Akhmedov , Kadriye Nur Saglam

Given a symplectic 4-manifold $(X,\omega)$ with rational symplectic form, Auroux constructed branched coverings to $(CP^2,\omega_{FS})$. By modifying a previous construction of Lambert-Cole--Meier--Starkston, we prove that the branch locus…

Geometric Topology · Mathematics 2024-03-11 Peter Lambert-Cole

We construct algebraic families of exotic affine 3-spheres, that is, smooth affine threefolds diffeomorphic to a non-degenerate smooth complex affine quadric of dimension 3 but non algebraically isomorphic to it. We show in particular that…

Algebraic Geometry · Mathematics 2016-10-06 Adrien Dubouloz