Dolgachev surface

In mathematics, Dolgachev surfaces are certain simply connected elliptic surfaces, introduced by Igor Dolgachev (1981). They can be used to give examples of an infinite family of homeomorphic simply connected compact 4-manifolds, no two of which are diffeomorphic.

## Properties

The blowup X0 of the projective plane in 9 points can be realized as an elliptic fibration all of whose fibers are irreducible. A Dolgachev surface Xq is given by applying logarithmic transformations of orders 2 and q to two smooth fibers for some q≥3.

The Dolgachev surfaces are simply connected, and the bilinear form on the second cohomology group is odd of signature (1,9) (so it is the unimodular lattice I1,9). The geometric genus pg is 0 and the Kodaira dimension is 1\.

Simon Donaldson (1987) found the first examples of homeomorphic but not diffeomorphic 4-manifolds X0 and X3. More generally the surfaces Xq and Xr are always homeomorphic, but are not diffeomorphic unless q=r.

Selman Akbulut (2012) showed that the Dolgachev surface X3 has a handlebody decomposition without 1- and 3-handles.

## References

* Akbulut, Selman (2012). "The Dolgachev surface. Disproving the Harer–Kas–Kirby conjecture". Commentarii Mathematici Helvetici 87 (1): 187–241. doi:10.4171/CMH/252. Bibcode: 2008arXiv0805.1524A.
* Barth, Wolf P.; Hulek, Klaus; Peters, Chris A.M.; Van de Ven, Antonius (2004). Compact Complex Surfaces. Ergebnisse der Mathematik und ihrer Grenzgebiete (3). 4. Springer-Verlag, Berlin. doi:10.1007/978-3-642-96754-2. ISBN 978-3-540-00832-3.
* Dolgachev, Igor (2010), "Algebraic surfaces with pg=g=0", Algebraic Surfaces, C.I.M.E. Summer Schools, 76, Heidelberg: Springer, pp. 97–215, doi:10.1007/978-3-642-11087-0_3
* Donaldson, Simon K. (1987). "Irrationality and the h-cobordism conjecture". Journal of Differential Geometry 26 (1): 141–168. doi:10.4310/jdg/1214441179. http://projecteuclid.org/euclid.jdg/1214441179.

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